[18]The existence of a molecule S6is known (up to 600°), and it must be held that this accounts for the formation of hydrogen persulphide, H2S5. Phosphorus appears in the molecule P4and gives P4H2. When expounding the data on specific heat we shall have occasion to return to the question of the complexity of the carbon molecule.[19]The hydrocarbons poor in hydrogen and containing many atoms of carbon, like chrysene and carbopetrocene, &c., CnH2(n-m), are solids, and less fusible asnandmincrease. They present a marked approach to the properties of the diamond. And in proportion to the diminution of the water in the carbohydrates CnH2mOm—for example in the humic compounds (Note5)—the transition of complex organic substances to charcoal is very evident. That residue resembling charcoal and graphite which is obtained by the separation (by means of copper sulphate and sodium chloride) of iron from white cast-iron containing carbon chemically combined with the iron, also seems, especially after the researches of G. A. Zaboudsky, to be a complex substance containing C12H6O3. The endeavours which have been directed towards determining the measure of complexity of the molecules of charcoal, graphite, and the diamond will probably at some period lead to the solution of this problem and will most likely prove that the various forms of charcoal, graphite, and the diamond contain molecules of different and very considerable complexity. The constancy of the grouping of benzene, C6H6, and the wide diffusion and facility of formation of the carbohydrates containing C6(for example, cellulose, C6H10O5, glucose, C6H12O6) give reason for thinking that the group C6is the first and simplest of those possible to free carbon, and it may be hoped that some time or other it may be possible to get carbon in this form. Perhaps in the diamond there may be found such a relation between the atoms as in the benzene group, and in charcoal such as in carbohydrates.[20]When charcoal burns, the complex molecule Cnis resolved into the simple moleculesnCO2, and therefore part of the heat—probably no small amount—is expended in the destruction of the complex molecule Cn. Perhaps by burning the most complex substances, which are the poorest as regards hydrogen, it may be possible to form an idea of the work required to split up Cninto separate atoms.[21]The viscosity, or degree of mobility, of liquids is determined by their internal friction. It is estimated by passing the liquids through narrow (capillary) tubes, the mobile liquids passing through with greater facility and speed than the viscid ones. The viscosity varies with the temperature and nature of the liquids, and in the case of solutions changes with the amount of the substance dissolved, but is not proportional to it. So that, for example, with alcohol at 20° the viscosity will be 69, and for a 50 p.c. solution 160, the viscosity of water being taken as 100. The volume of the liquid which passes through by experiment (Poiseuille) and theory (Stokes) is proportional to the time, the pressure, and the fourth power of the diameter of the (capillary) tube, and inversely proportional to the length of the tube; this renders it possible to form comparative estimates of the coefficients of internal friction and viscosity.As the complexity of the molecules of hydrocarbons and their derivatives increases by the addition of carbon (or CH2), so does the degree of viscosity also rise. The extensive series of investigations referring to this subject still await the necessary generalisation. That connection which (already partly observed) ought to exist between the viscosity and the other physical and chemical properties, forces us to conclude that the magnitude of internal friction plays an important part in molecular mechanics. In investigating organic compounds and solutions, similar researches ought to stand foremost. Many observations have already been made, but not much has yet been done with them; the bare facts and some mechanical data exist, but their relation to molecular mechanics has not been cleared up in the requisite degree. It has already been seen from existing data that the viscosity at the temperature of the absolute boiling point becomes as small as in gases.[22]In a number of hydrocarbons and their derivatives such a substitution of metals for the hydrogen may be attained by indirect means. The property shown by acetylene, C2H2, and its analogues, of forming metallic derivatives is in this respect particularly characteristic. Judging from the fact that carbon is an acid element (that is, gives an acid anhydride with oxygen), though comparatively slightly acid (for carbonic acid is not at all a strong acid and compounds of chlorine and carbon, even CCl4, are not decomposed by water as is the case with phosphorus chloride and even silicic chloride and boric chloride, although they correspond with acids of but little energy), one might expect to find in the hydrogen of hydrocarbons this faculty for being substituted by metals. The metallic compounds which correspond with hydrocarbons are known under the name of organo-metallic compounds. Such, for instance, is zinc ethyl, Zn(C2H5)2, which corresponds with ethyl hydride or ethane, C2H6, in which two atoms of hydrogen have been exchanged for one of zinc.[23]Gaseous and volatile hydrocarbons decompose when passed through a heated tube. When hydrocarbons are decomposed by heating, the primary products are generally other more stable hydrocarbons, among which are acetylene, C2H2, benzene, C6H6, naphthalene, C10H8, &c.[24]Wagner (1888) showed that when unsaturated hydrocarbons are shaken with a weak (1 p.c.) solution of potassium permanganate, KMnO4, at ordinary temperatures, they form glycols—for example, C2H4yields C2H6O2.[25]My article on this subject appeared in the Journal of the St. Petersburg Academy of Sciences in 1861. Up to that time, although many additive combinations with hydrocarbons and their derivatives were known, they had not been generalised, and were even continually quoted as cases of substitution. Thus the combination of ethylene, C2H4, with chlorine, Cl2, was often regarded as a formation of the products of the substitution of C2H5Cl and HCl, which it was supposed were held together as the water of crystallisation is in salts. Even earlier than this (1857,Journal of the Petroffsky Academy) I considered similar cases as true compounds. In general, according to the law of limits, an unsaturated hydrocarbon, or its derivative, on combining withrX2, gives a substance which is saturated or else approaching the limit. The investigations of Frankland with many organo-metallic compounds clearly showed the limit in the case of metallic compounds, which we shall constantly refer to later on.[26]The conception of homology has been applied by Gerhardt to all organic compounds in his classical work, ‘Traité de Chimie Organique,’ finished in 1855 (4 vols.), in which he divided all organic compounds intofattyandaromatic, which is in principle still adhered to at the present time, although the latter are more often called benzene derivatives, on account of the fact that Kekulé, in his beautiful investigations on the structure of aromatic compounds, showed the presence in them all of the ‘benzene nucleus,’ C6H6.[27]This is always true for hydrocarbons, but for derivatives of the lower homologues the law is sometimes different; for instance, in the series of saturated alcohols, CnH2n+1(OH), whenn= 0, we obtain water, H(OH), which boils at 100°, and whose specific gravity at 15° = 0·9992; whenn= 1, wood spirit CH3(OH), which boils at 66°, and at 15° has a specific gravity = 0·7964; whenn= 2, ordinary alcohol, C2H5(OH), boiling at 78°, specific gravity at 15° = 0·7936, and with further increase of CH2the specific gravity increases. For the glycols CnH2n(OH)2the phenomenon of a similar kind is still more striking; at first the temperature of the boiling point and the density increase, and then for higher (more complex) members of the series diminish. The reason for this phenomenon, it is evident, must be sought for in the influence and properties of water, and that strong affinity which, acting between hydrogen and oxygen, determines many of the exceptional properties of water (ChapterI.).[28]As, for example, in the saturated series of hydrocarbons CnH2n+2, the lowest member (n= 0) must be taken as hydrogen H2, a gas which (t.c.below -190°) is liquefied with great difficulty, and when in a liquid state has doubtless a very small density. Wheren= 1, 2, 3, the hydrocarbons CH4, C2H6, C3H8are gases, more and more readily liquefiable. The temperature of the absolute boiling point for CH4= -100°, and for ethane C2H6, and in the higher members it rises. The hydrocarbon C4H10, liquefies at about 0°. C5H12(there are several isomers) boils at from +9° (Lvoff) to 37°, C6H14from 58° to 78°, &c. The specific gravities in a liquid state at 15° are:—C5H12C6H14C7H16C10H22C16H340·630·660·700·750·85[29]If, at the ordinary temperature (assuming therefore that the water formed will be in a liquid state) a gram molecule (26 grams) of acetylene, C2H2, be burnt, 310 thousand calories will be emitted (Thomsen), and as 12 grams of charcoal produce 97 thousand calories, and 2 grams of hydrogen 69 thousand calories, it follows that, if the hydrogen and carbon of the acetylene were burnt there would be only 2 × 97 + 69, or 263 thousand calories produced. It is evident, then, that acetylene in its formation absorbs 310–263, or 47 thousand calories.For considerations relative to the combustion of carbon compounds, we will first enumerate the quantity of heat separated by the combustion of definite chemical carbon compounds, and then give a few figures bearing on the kinds of fuel used in practice.For molecular quantities in perfect combustion the following amounts of heat are given out (when gaseous carbonic anhydride and liquid water are formed), according to Thomsen's data (1) for gaseous CnH2n+2: 52·8 + 158·8nthousand calories; (2) for CnH2n: 17·7 + 158·1nthousand calories; (3) according to Stohmann (1888) for liquid saturated alcohols, CnH2n+2O: 11·8 + 156·3n, and as the latent heat of evaporation = about 8·2 + 0·6n, in a gaseous state, 20·0 + 156·9n; (4) for monobasic saturated liquid acids, CnH2nO2:—95·3 + 154·3n, and as their latent heat of evaporation is about 5·0 + 1·2n, in a gaseous form, about—90 + 155n; (5) for solid saturated bibasic acids, CnH2n-2O4:—253·8 + 152·6n, if they are expressed as CnH2nC2H2O4, then 51·4 + 152·6n; (6) for benzene and its liquid homologues (still according to Stohmann) CnH2n-6:—158·6 + 156·3n, and in a gaseous form about—155 + 157n; (7) for the gaseous homologues of acetylene, CnH2n-2(according to Thomsen)—5 + 157n. It is evident from the preceding figures that the group CH2, or CH3substituted for H, on burning gives out from 152 to 159 thousand calories. This is less than that given out by C + H2, which is 97 + 69 or 166 thousand; the reason for this difference (it would be still greater if carbon were gaseous) is the amount of heat separated during the formation of CH2. According to Stohmann, for dextroglucose, C6H12O6, it is 673·7; for common sugar, C12H22O11, 1325·7; for cellulose, C6H10O5, 678·0; starch, 677·5; dextrin, 666·2; glycol, C2H6O2, 281·7; glycerine, 397·2, &c. The heat of combustion of the following solids (determined by Stohmann) is expressed per unit of weight: naphthalene, C10H8, 9,621; urea, CN2H4O, 2,465; white of egg, 5,579; dry rye bread, 4,421; wheaten bread, 4,302; tallow, 9,365; butter, 9,192; linseed oil, 9,323. The most complete collection of arithmetical data for the heats of combustion will be found in V. F. Longinin's work, ‘Description of the Various Methods of Determining the Heats of Combustion of Organic Compounds’ (Moscow, 1894).The number of units of heat given out byunit weightduring the complete combustion and cooling of the following ordinary kinds of fuel in their usual state of dryness and purity are:—(1) for wood charcoal, anthracite, semi-anthracite, bituminous coal and coke, from 7,200 to 8,200; (2) dry, long flaming coals, and the best brown coals, from 6,200 to 6,800; (3) perfectly dry wood, 3,500; hardly dry, 2,500; (4) perfectly dry peat, best kind, 4,500; compressed and dried, 3,000; (5) petroleum refuse and similar liquid hydrocarbons, about 11,000; (6) illuminating gas of the ordinary composition (about 45 vols. H, 40 vols. CH4, 5 vols. CO, and 5 vols. N), about 12,000; (7) producer gas (seenext Chapter), containing 2 vols. carbonic anhydride, 30 vols. carbonic oxide, and 68 vols. nitrogenfor one part by weight of the whole carbon burnt, 5,300, and for one part by weight of the gas, 910, units of heat; and (8) water gas (seenext chapter) containing 4 vols. carbonic anhydride, 8 vols. N2, 24 vols. carbonic oxide, and 46 vols. H2, for one part by weight of the carbon consumed in thegenerator10,900, and for one part by weight of the gas, 3,600 units of heat. In these figures, as in all calorimetric observations, the water produced by the combustion of the fuel is supposed to be liquid. As regards the temperature reached by the fuel, it is important to remark that for solid fuel it is indispensable to admit (to ensure complete combustion) twice the amount of air required, but liquid, or pulverised fuel, and especially gaseous fuel, does not require an excess of air; therefore, a kilogram of charcoal, giving 8,000 units of heat, requires about 24 kilograms of air (3 kilograms of air per thousand calories) and a kilogram of producer gas requires only 0·77 kilogram of air (0·85 kilo. of air per 1,000 calories), 1 kilogram of water gas about 4·5 of air (1·25 kilo. of air per 1,000 calories).[29 bis]Manure which decomposes under the action of bacteria gives off CO2and CH4.[30]It is easy to collect the gas which is evolved in marshy places if a glass bottle be inverted in the water and a funnel put into it (both filled with water); if the mud of the bottom be now agitated, the bubbles which rise may be easily caught by the inverted funnel.[31]see captionFig.58.—General view of gas works.B, retorts;f, hydraulic main;HandI, tar well;i, condensers;L, purifiers;P, gasholder.see captionFig.59.—Blowpipe. Air is blown in at the trumpet-shaped mouthpiece, and escapes in a fine stream from the platinum jet placed at the extremity of the side tube.see captionFig.60.—Davy safety-lamp. [Modern form.]Illuminating gas is generally prepared by heating gas coal (seeNote6) in oval cylindrical horizontal cast-iron or clay retorts. Several such retortsBB(fig.58) are disposed in the furnaceA, and heated together. When the retorts are heated to a red heat, lumps of coal are thrown into them, and they are then closed with a closely fitting cover. The illustration shows the furnace, with five retorts. Coke (seeNote1, dry distillation) remains in the retorts, and the volatile products in the form of vapours and gases travel along the piped, rising from each retort. These pipes branch above the stove, and communicate with the receiverf(hydraulic main) placed above the furnace. Those products of the dry distillation which most easily pass from the gaseous into the liquid and solid states collect in the hydraulic main. From the hydraulic main the vapours and gases travel along the pipegand the series of vertical pipesj(which are sometimes cooled by water trickling over the surface), where the vapours and gases cool from the contact of the colder surface, and a fresh quantity of vapour condenses. The condensed liquids pass from the pipesgandjand into the troughsH. These troughs always contain liquid at a constant level (the excess flowing away) so that the gas cannot escape, and thus they form, as it is termed, a hydraulic joint. In the state in which it leaves the condensers the gas consists principally of the following vapours and gases: (1) vapour of water, (2) ammonium carbonate, (3) liquid hydrocarbons, (4) hydrogen sulphide, H2S, (5) carbonic anhydride, CO2, (6) carbonic oxide, CO, (7) sulphurous anhydride, SO2, but a great part of the illuminating gas consists of (8) hydrogen, (9) marsh gas, (10) olefiant gas, C2H4, and other gaseous hydrocarbons. The hydrocarbons (3, 9, and 10), the hydrogen, and carbonic oxide are capable of combustion, and are useful component parts, but the carbonic anhydride, the hydrogen sulphide, and sulphurous anhydride, as well as the vapours of ammonium carbonate, form an injurious admixture, because they do not burn (CO2, SO2) and lower the temperature and brilliancy of the flame, or else, although capable of burning (for example, H2S, CS2, and others), they give out during combustion sulphurous anhydride which has a disagreeable smell, is injurious when inhaled, and spoils many surrounding objects. In order to separate the injurious products, the gas is washed with water, a cylinder (not shown in the illustration) filled with coke continually moistened with water serving for this purpose. The water coming into contact with the gas dissolves the ammonium carbonate; hydrogen sulphide, carbonic anhydride, and sulphurous anhydride, being only partly soluble in water, have to be got rid of by a special means. For this purpose the gas is passed through moist lime or other alkaline liquid, as the above-mentioned gases have acid properties and are therefore retained by the alkali. In the case of lime, calcium carbonate, sulphite and sulphide, all solid substances, are formed. It is necessary to renew the purifying material as its absorbing power decreases. A mixture of lime and sulphate of iron, FeSO4, acts still better, because the latter, with lime, Ca(HO)2, forms ferrous hydroxide, Fe(HO)2and gypsum, CaSO4. The suboxide (partly turning into oxide) of iron absorbs H2S, forming FeS and H2O, and the gypsum retains the remainder of the ammonia, the excess of lime absorbing carbonic anhydride and sulphuric anhydride. [In English works a native hydrated ferric hydroxide is used for removing hydrogen sulphide.] This purification of the gas takes place in the apparatusL, where the gas passes through perforated traysm, covered with sawdust mixed with lime and sulphate of iron. It is necessary to remark that in the manufacture of gas it is indispensable to draw off the vapours from the retorts, so that they should not remain there long (otherwise the hydrocarbons would in a considerable degree be resolved into charcoal and hydrogen), and also to avoid a great pressure of gas in the apparatus, otherwise a quantity of gas would escape at all cracks such as must inevitably exist in such a complicated arrangement. For this purpose there are special pumps (exhausters) so regulated that they only pump off the quantity of gas formed (the pump is not shown in the illustration). The purified gas passes through the pipeninto the gasometer (gasholder)P, a dome made of iron plate. The edges of the dome dip into water poured into a ring-shaped channelg, in which the sides of the dome rise and fall. The gas is collected in this holder, and distributed to its destination by pipes communicating with the pipeo, issuing from the dome. The pressure of the dome on the gas enables it, on issuing from a long pipe, to penetrate through the small aperture of the burner. A hundred kilograms of coal give about 20 to 30 cubic metres of gas, having a density from four to nine times greater than that of hydrogen. A cubic metre (1,000 litres) of hydrogen weighs about 87 grams; therefore 100 kilograms of coal give about 18 kilograms of gas, or about one-sixth of its weight. Illuminating gas is generally lighter than marsh gas, as it contains a considerable amount of hydrogen, and is only heavier than marsh gas when it contains much of the heavier hydrocarbons. Thus olefiant gas, C2H4, is fourteen times, and the vapours of benzene thirty-nine times, heavier than hydrogen, and illuminating gas sometimes contains 15 p.c. of its volume of them. The brilliancy of the flame of the gas increases with the quantity of olefiant gas and similar heavy hydrocarbons, as it then contains more carbon for a given volume and a greater number of carbon particles are separated. Gas usually contains from 35 to 60 p.c. of its volume of marsh gas, from 30 to 50 p.c. of hydrogen, from 3 to 5 p.c. of carbonic oxide, from 2 to 10 p.c. heavy hydrocarbons, and from 3 to 10 p.c. of nitrogen. Wood gives almost the same sort of gas as coal and almost the same quantity, but the wood gas contains a great deal of carbonic anhydride, although on the other hand there is an almost complete absence of sulphur compounds. Tar, oils, naphtha, and such materials furnish a large quantity of good illuminating gas. An ordinary burner of 8 to 12 candle-power burns 5 to 6 cubic feet of coal gas per hour, but only 1 cubic foot of naphtha gas. One pood (36 lbs. Eng.) of naphtha gives 500 cubic feet of gas—that is, one kilogram of naphtha produces about one cubic metre of gas. The formation of combustible gas by heating coal was discovered in the beginning of the last century, but only put into practice towards the end by Le-Bon in France and Murdoch in England. In England, Murdoch, together with the renowned Watt, built the first gas works in 1805.In practice illuminating gas is not only used for lighting (electricity and kerosene are cheaper in Russia), but also as the motive power for gas engines (seep.175), which consume about half a cubic metre per horse-power per hour; gas is also used in laboratories for heating purposes. When it is necessary to concentrate the heat, either the ordinary blowpipe (fig.59) is applied, placing the end in the flame and blowing through the mouthpiece; or, in other forms, gas is passed through the blowpipe; when a large, hot, smokeless flame is required for heating crucibles or glass-blowing, a foot-blower is used. High temperatures, which are often required for laboratory and manufacturing purposes, are most easily attained by the use of gaseous fuel (illuminating gas, producer gas, and water gas, which will be treated of in thefollowing chapter), because complete combustion may be effected without an access of air. It is evident that in order to obtain high temperatures means must be taken to diminish the loss of heat by radiation, and to ensure perfect combustion.[32]The gas which is set free in coal mines contains a good deal of nitrogen, some carbonic anhydride, and a large quantity of marsh gas. The best means of avoiding an explosion consists in efficient ventilation. It is best to light coal mines with electric lamps.[33]The Davy lamp, of which an improved form is represented in the accompanying figure, is used for lighting coal and other mines where combustible gas is found. The wick of the lamp is enclosed in a thick glass cylinder which is firmly held in a metallic holder. Over this a metallic cylinder and the wire gauze are placed. The products of combustion pass through the gauze, and the air enters through the space between the cylinder and the wire gauze. To ensure greater safety the lamp cannot be opened without extinguishing the flame.[34]In Pennsylvania (beyond the Alleghany mountains) many of the shafts sunk for petroleum only emitted gas, but many useful applications for it were found and it was conducted in metallic pipes to works hundreds of miles distant, principally for metallurgical purposes.[35]The purest gas is prepared by mixing the liquid substance called zinc methyl, Zn(CH3)2, with water, when the following reaction occurs:Zn(CH3)2+ 2HOH = Zn(HO)2+ 2CH3H.[36]Methylene, CH2, does not exist. When attempts are made to obtain it (for example, by removing X2from CH2X2), C2H4or C3H6are produced—that is to say, it undergoes polymerisation.[37]Although the methods of formation and the reactions connected with hydrocarbons are not described in this work, because they are dealt with in organic chemistry, yet in order to clearly show the mechanism of those transformations by which the carbon atoms are built up into the molecules of the carbon compounds, we here give a general example of reactions of this kind. From marsh gas, CH4, on the one hand the substitution of chlorine or iodine, CH3Cl, CH3I, for the hydrogen may be effected, and on the other hand such metals as sodium may be substituted for the hydrogen,e.g.CH3Na. These and similar products of substitution serve as a means of obtaining other more complex substances from given carbon compounds. If we place the two above-named products of substitution of marsh gas (metallic and haloid) in mutual contact, the metal combines with the halogen, forming a very stable compound—namely, common salt, NaCl, and the carbon groups which were in combination with them separate in mutual combination, as shown by the equation:CH3Cl + CH3Na = NaCl + C2H6.This is the most simple example of the formation of a complex hydrocarbon from these radicles. The cause of the reaction must be sought for in the property which the haloid (chlorine) and sodium have of entering into mutual combination.[38]Whenm=n- 1, we have the series CnH2. The lowest member is acetylene, C2H2. These are hydrocarbons containing a minimum amount of hydrogen.[39]For instance, ethylene, C2H4, combines with Br2, HI, H2SO4, as a whole molecule, as also does amylene, C5H10, and, in general, CnH2n.[40]For instance, ethylene is obtained by removing the water from ethyl alcohol, C2H5(OH), and amylene, C5H10, from amyl alcohol, C5H11(OH), or in general CnH2n, from CnH2n+1(OH).[41]Acetylene and its polymerides have an empirical composition CH, ethylene and its homologues (and polymerides) CH2, ethane CH3, methane CH4. This series presents a good example of the law of multiple proportions, but such diverse proportions are met with between the number of atoms of the carbon and hydrogen in the hydrocarbons already known that the accuracy of Dalton's law might be doubted. Thus the substances C30H62and C30H60differ so slightly in their composition by weight as to be within the limits of experimental error, but their reactions and properties are so distinct that they can be distinguished beyond a doubt. Without Dalton's law chemistry could not have been brought to its present condition, but it cannot alone express all those gradations which are quite clearly understood and predicted by the law of Avogadro-Gerhardt.[42]The conception of the structure of carbon compounds—that is, the expression of those unions and correlations which their atoms have in the molecules—was for a long time limited to the representation that organic substances contained complex radicles (for instance, ethyl C2H5, methyl CH3, phenyl C6H5, &c.); then about the year 1840 the phenomena of substitution and the correspondence of the products of substitution with the primary bodies (nuclei and types) were observed, but it was not until about the year 1860 and later when on the one hand the teaching of Gerhardt about molecules was spreading, and on the other hand the materials had accumulated for discussing the transformations of the simplest hydrocarbon compounds, that conjectures began to appear as to the mutual connection of the atoms of carbon in the molecules of the complex hydrocarbon compounds. Then Kekulé and A. M. Butleroff began to formulate the connection between the separate atoms of carbon, regarding it as a quadrivalent element. Although in their methods of expression and in some of their views they differ from each other and also from the way in which the subject is treated in this work, yet the essence of the matter—namely, the comprehension of the causes of isomerism and of the union between the separate atoms of carbon—remains the same. In addition to this, starting from the year 1870, there appears a tendency which from year to year increases to discover the actual spacial distribution of the atoms in the molecules. Thanks to the endeavours of Le-Bel (1874), Van't Hoff (1874), and Wislicenus (1887) in observing cases of isomerism—such as the effect of different isomerides on the direction of the rotation of the plane of polarisation of light—this tendency promises much for chemical mechanics, but the details of the still imperfect knowledge in relation to this matter must be sought for in special works devoted to organic chemistry.[43]Direct experiment shows that however CH3X is prepared (where X = for instance Cl, &c.) it is always one and the same substance. If, for example, in CX4, X is gradually replaced by hydrogen until CH3X is produced, or in CH4, the hydrogen by various means is replaced by X, or else, for instance, if CH3X be obtained by the decomposition of more complex compounds, the same product is always obtained.This was shown in the year 1860, or thereabout, by many methods, and is the fundamental conception of the structure of hydrocarbon compounds. If the atoms of hydrogen in methyl were not absolutely identical in value and position (as they are not, for instance, in CH3CH2CH3or CH3CH2X), then there would be as many different forms of CH3X as there were diversities in the atoms of hydrogen in CH4. The scope of this work does not permit of a more detailed account of this matter. It is given in works on organic chemistry.[44]The union of carbon atoms in closed chains or rings was first suggested by Kekulé as an explanation of the structure and isomerism of the derivatives of benzene, C6H6, forming aromatic compounds (Note26).[45]The following are the most generally known of the oxygenised but non-nitrogenous hydrocarbon derivatives. (1) the alcohols. These are hydrocarbons in which hydrogen is exchanged for hydroxyl (OH). The simplest of these is methyl alcohol, CH3(OH), or wood spirit obtained by the dry distillation of wood. The common spirits of wine or ethyl alcohol, C2H3(OH), and glycol, C2H4(OH)2, correspond with ethane. Normal propyl alcohol, CH3CH2CH2(OH), and isopropyl alcohol, CH3CH(OH)CH3, propylene-glycol, C3H6(OH)2, and glycerol, C3H3(OH)3(which, with stearic and other acids, forms fatty substances), correspond with propane, C3H8. All alcohols are capable of forming water and ethereal salts with acids, just as alkalis form ordinary salts. (2) Aldehydes are alcohols minus hydrogen; for instance, acetaldehyde, C2H4O, corresponds with ethyl alcohol. (3) It is simplest to regard organic acids as hydrocarbons in which hydrogen has been exchanged for carboxyl (CO2H), as will be explained in thefollowing chapter. There are a number of intermediate compounds; for example, the aldehyde-alcohols, alcohol-acids (or hydroxy-acids), &c. Thus the hydroxy-acids are hydrocarbons in which some of the hydrogen has been replaced by hydroxyl, and some by carboxyl; for instance, lactic acid corresponds with C2H6, and has the constitution C2H4(OH)(CO2H). If to these products we add the haloid salts (where H is replaced by Cl, Br, I), the nitro-compounds containing NO2in place of H, the amides, cyanides, ketones, and other compounds, it will be readily seen what an immense number of organic compounds there are and what a variety of properties these substances have; this we see also from the composition of plants and animals.[46]Ethylene bromide, C2H4Br2, when gently heated in alcoholic solution with finely divided zinc, yields pure ethylene, the zinc merely taking up the bromine (Sabaneyeff).[47]Ethylene decomposes somewhat easily under the influence of the electric spark, or a high temperature. In this case the volume of the gas formed may remain the same when olefiant gas is decomposed into carbon and marsh gas, or may increase to double its volume when hydrogen and carbon are formed, C2H4= CH4+ C = 2C + 2H2. A mixture of olefiant gas and oxygen is highly explosive; two volumes of this gas require six volumes of oxygen for its perfect combustion. The eight volumes thus taken then resolve themselves into eight volumes of the products of combustion, a mixture of water and carbonic anhydride, C2H4+ 3O2= 2CO2+ 2H2O. On cooling after the explosion diminution of volume occurs because the water becomes liquid. For two volumes of the olefiant gas taken, the diminution will be equal to four volumes, and the same for marsh gas. The quantity of carbonic anhydride formed by both gases is not the same. Two volumes of marsh gas give only two volumes of carbonic anhydride, and two volumes of ethylene give four volumes of carbonic anhydride.[48]The homologues of ethylene, CnH2n, are also capable of direct combination with halogens, &c., but with various degrees of facility. The composition of these homologues can be expressed thus: (CH3)_x(CH2)y(CH)zCr, where the sum ofx+zis always an even number, and the sum ofx+z+ris equal to half the sum of 3x+z, whencez+ 2r=x; by this means the possible isomerides are determined. For example, for butylenes, C4H8, (CH3)2(CH)2, (CH3)2(CH2)C, (CH2)(CH2)2CH, and (CH2)4are possible.[48 bis]Seealso method of preparing C2H2in Note12 bis.[49]This is easily accomplished with those gas burners which are used in laboratories and mentioned in the Introduction. In these burners the gas is first mixed with air in a long tube, above which it is kindled. But if it be lighted inside the pipe it does not burn completely, but forms acetylene, on account of the cooling effect of the walls of the metallic tube; this is detected by the smell, and may be shown by passing the issuing gas (by aid of an aspirator) into an ammoniacal solution of cuprous chloride.[50]Amongst the homologues of acetylene CnH2n-2, the lowest is C3H4; allylene, CH3CCH, and allene, CH2CCH2, are known, but the closed structure, CH2(CH)2, is little investigated.[51]The saturated hydrocarbons predominate in American petroleum, especially in its more volatile parts; in Baku naphtha the hydrocarbons of the composition CnH2nform the main part (Lisenko, Markovnikoff, Beilstein) but doubtless (Mendeléeff) it also contains saturated ones, CnH2n+2. The structure of the naphtha hydrocarbons is only known for the lower homologues, but doubtless the distinction between the hydrocarbons of the Pennsylvanian and Baku naphthas, boiling at the same temperature (after the requisite refining by repeated fractional distillation, which can be very conveniently done by means of steam rectification—that is, by passing the steam through the dense mass), depends not only on the predominance of saturated hydrocarbons in the former, and naphthenes, CnH2n, in the latter, but also on the diversity of composition and structure of the corresponding portions of the distillation. The products of the Baku naphtha are richer in carbon (therefore in a suitably constructed lamp they ought to give a brighter light), they are of greater specific gravity, and have greater internal friction (and are therefore more suitable for lubricating machinery) than the American products collected at the same temperature.[52]The formation of naphtha fountains (which burst forth after the higher clay strata covering the layers of sands impregnated with naphtha have been bored through) is without doubt caused by the pressure or tension of the combustible hydrocarbon gases which accompany the naphtha, and are soluble in it under pressure. Sometimes these naphtha fountains reach a height of 100 metres—for instance, the fountain of 1887 near Baku. Naphtha fountains generally act periodically and their force diminishes with the lapse of time, which might be expected, because the gases which cause the fountains find an outlet, as the naphtha issuing from the bore-hole carries away the sand which was partially choking it up.
[18]The existence of a molecule S6is known (up to 600°), and it must be held that this accounts for the formation of hydrogen persulphide, H2S5. Phosphorus appears in the molecule P4and gives P4H2. When expounding the data on specific heat we shall have occasion to return to the question of the complexity of the carbon molecule.
[18]The existence of a molecule S6is known (up to 600°), and it must be held that this accounts for the formation of hydrogen persulphide, H2S5. Phosphorus appears in the molecule P4and gives P4H2. When expounding the data on specific heat we shall have occasion to return to the question of the complexity of the carbon molecule.
[19]The hydrocarbons poor in hydrogen and containing many atoms of carbon, like chrysene and carbopetrocene, &c., CnH2(n-m), are solids, and less fusible asnandmincrease. They present a marked approach to the properties of the diamond. And in proportion to the diminution of the water in the carbohydrates CnH2mOm—for example in the humic compounds (Note5)—the transition of complex organic substances to charcoal is very evident. That residue resembling charcoal and graphite which is obtained by the separation (by means of copper sulphate and sodium chloride) of iron from white cast-iron containing carbon chemically combined with the iron, also seems, especially after the researches of G. A. Zaboudsky, to be a complex substance containing C12H6O3. The endeavours which have been directed towards determining the measure of complexity of the molecules of charcoal, graphite, and the diamond will probably at some period lead to the solution of this problem and will most likely prove that the various forms of charcoal, graphite, and the diamond contain molecules of different and very considerable complexity. The constancy of the grouping of benzene, C6H6, and the wide diffusion and facility of formation of the carbohydrates containing C6(for example, cellulose, C6H10O5, glucose, C6H12O6) give reason for thinking that the group C6is the first and simplest of those possible to free carbon, and it may be hoped that some time or other it may be possible to get carbon in this form. Perhaps in the diamond there may be found such a relation between the atoms as in the benzene group, and in charcoal such as in carbohydrates.
[19]The hydrocarbons poor in hydrogen and containing many atoms of carbon, like chrysene and carbopetrocene, &c., CnH2(n-m), are solids, and less fusible asnandmincrease. They present a marked approach to the properties of the diamond. And in proportion to the diminution of the water in the carbohydrates CnH2mOm—for example in the humic compounds (Note5)—the transition of complex organic substances to charcoal is very evident. That residue resembling charcoal and graphite which is obtained by the separation (by means of copper sulphate and sodium chloride) of iron from white cast-iron containing carbon chemically combined with the iron, also seems, especially after the researches of G. A. Zaboudsky, to be a complex substance containing C12H6O3. The endeavours which have been directed towards determining the measure of complexity of the molecules of charcoal, graphite, and the diamond will probably at some period lead to the solution of this problem and will most likely prove that the various forms of charcoal, graphite, and the diamond contain molecules of different and very considerable complexity. The constancy of the grouping of benzene, C6H6, and the wide diffusion and facility of formation of the carbohydrates containing C6(for example, cellulose, C6H10O5, glucose, C6H12O6) give reason for thinking that the group C6is the first and simplest of those possible to free carbon, and it may be hoped that some time or other it may be possible to get carbon in this form. Perhaps in the diamond there may be found such a relation between the atoms as in the benzene group, and in charcoal such as in carbohydrates.
[20]When charcoal burns, the complex molecule Cnis resolved into the simple moleculesnCO2, and therefore part of the heat—probably no small amount—is expended in the destruction of the complex molecule Cn. Perhaps by burning the most complex substances, which are the poorest as regards hydrogen, it may be possible to form an idea of the work required to split up Cninto separate atoms.
[20]When charcoal burns, the complex molecule Cnis resolved into the simple moleculesnCO2, and therefore part of the heat—probably no small amount—is expended in the destruction of the complex molecule Cn. Perhaps by burning the most complex substances, which are the poorest as regards hydrogen, it may be possible to form an idea of the work required to split up Cninto separate atoms.
[21]The viscosity, or degree of mobility, of liquids is determined by their internal friction. It is estimated by passing the liquids through narrow (capillary) tubes, the mobile liquids passing through with greater facility and speed than the viscid ones. The viscosity varies with the temperature and nature of the liquids, and in the case of solutions changes with the amount of the substance dissolved, but is not proportional to it. So that, for example, with alcohol at 20° the viscosity will be 69, and for a 50 p.c. solution 160, the viscosity of water being taken as 100. The volume of the liquid which passes through by experiment (Poiseuille) and theory (Stokes) is proportional to the time, the pressure, and the fourth power of the diameter of the (capillary) tube, and inversely proportional to the length of the tube; this renders it possible to form comparative estimates of the coefficients of internal friction and viscosity.As the complexity of the molecules of hydrocarbons and their derivatives increases by the addition of carbon (or CH2), so does the degree of viscosity also rise. The extensive series of investigations referring to this subject still await the necessary generalisation. That connection which (already partly observed) ought to exist between the viscosity and the other physical and chemical properties, forces us to conclude that the magnitude of internal friction plays an important part in molecular mechanics. In investigating organic compounds and solutions, similar researches ought to stand foremost. Many observations have already been made, but not much has yet been done with them; the bare facts and some mechanical data exist, but their relation to molecular mechanics has not been cleared up in the requisite degree. It has already been seen from existing data that the viscosity at the temperature of the absolute boiling point becomes as small as in gases.
[21]The viscosity, or degree of mobility, of liquids is determined by their internal friction. It is estimated by passing the liquids through narrow (capillary) tubes, the mobile liquids passing through with greater facility and speed than the viscid ones. The viscosity varies with the temperature and nature of the liquids, and in the case of solutions changes with the amount of the substance dissolved, but is not proportional to it. So that, for example, with alcohol at 20° the viscosity will be 69, and for a 50 p.c. solution 160, the viscosity of water being taken as 100. The volume of the liquid which passes through by experiment (Poiseuille) and theory (Stokes) is proportional to the time, the pressure, and the fourth power of the diameter of the (capillary) tube, and inversely proportional to the length of the tube; this renders it possible to form comparative estimates of the coefficients of internal friction and viscosity.
As the complexity of the molecules of hydrocarbons and their derivatives increases by the addition of carbon (or CH2), so does the degree of viscosity also rise. The extensive series of investigations referring to this subject still await the necessary generalisation. That connection which (already partly observed) ought to exist between the viscosity and the other physical and chemical properties, forces us to conclude that the magnitude of internal friction plays an important part in molecular mechanics. In investigating organic compounds and solutions, similar researches ought to stand foremost. Many observations have already been made, but not much has yet been done with them; the bare facts and some mechanical data exist, but their relation to molecular mechanics has not been cleared up in the requisite degree. It has already been seen from existing data that the viscosity at the temperature of the absolute boiling point becomes as small as in gases.
[22]In a number of hydrocarbons and their derivatives such a substitution of metals for the hydrogen may be attained by indirect means. The property shown by acetylene, C2H2, and its analogues, of forming metallic derivatives is in this respect particularly characteristic. Judging from the fact that carbon is an acid element (that is, gives an acid anhydride with oxygen), though comparatively slightly acid (for carbonic acid is not at all a strong acid and compounds of chlorine and carbon, even CCl4, are not decomposed by water as is the case with phosphorus chloride and even silicic chloride and boric chloride, although they correspond with acids of but little energy), one might expect to find in the hydrogen of hydrocarbons this faculty for being substituted by metals. The metallic compounds which correspond with hydrocarbons are known under the name of organo-metallic compounds. Such, for instance, is zinc ethyl, Zn(C2H5)2, which corresponds with ethyl hydride or ethane, C2H6, in which two atoms of hydrogen have been exchanged for one of zinc.
[22]In a number of hydrocarbons and their derivatives such a substitution of metals for the hydrogen may be attained by indirect means. The property shown by acetylene, C2H2, and its analogues, of forming metallic derivatives is in this respect particularly characteristic. Judging from the fact that carbon is an acid element (that is, gives an acid anhydride with oxygen), though comparatively slightly acid (for carbonic acid is not at all a strong acid and compounds of chlorine and carbon, even CCl4, are not decomposed by water as is the case with phosphorus chloride and even silicic chloride and boric chloride, although they correspond with acids of but little energy), one might expect to find in the hydrogen of hydrocarbons this faculty for being substituted by metals. The metallic compounds which correspond with hydrocarbons are known under the name of organo-metallic compounds. Such, for instance, is zinc ethyl, Zn(C2H5)2, which corresponds with ethyl hydride or ethane, C2H6, in which two atoms of hydrogen have been exchanged for one of zinc.
[23]Gaseous and volatile hydrocarbons decompose when passed through a heated tube. When hydrocarbons are decomposed by heating, the primary products are generally other more stable hydrocarbons, among which are acetylene, C2H2, benzene, C6H6, naphthalene, C10H8, &c.
[23]Gaseous and volatile hydrocarbons decompose when passed through a heated tube. When hydrocarbons are decomposed by heating, the primary products are generally other more stable hydrocarbons, among which are acetylene, C2H2, benzene, C6H6, naphthalene, C10H8, &c.
[24]Wagner (1888) showed that when unsaturated hydrocarbons are shaken with a weak (1 p.c.) solution of potassium permanganate, KMnO4, at ordinary temperatures, they form glycols—for example, C2H4yields C2H6O2.
[24]Wagner (1888) showed that when unsaturated hydrocarbons are shaken with a weak (1 p.c.) solution of potassium permanganate, KMnO4, at ordinary temperatures, they form glycols—for example, C2H4yields C2H6O2.
[25]My article on this subject appeared in the Journal of the St. Petersburg Academy of Sciences in 1861. Up to that time, although many additive combinations with hydrocarbons and their derivatives were known, they had not been generalised, and were even continually quoted as cases of substitution. Thus the combination of ethylene, C2H4, with chlorine, Cl2, was often regarded as a formation of the products of the substitution of C2H5Cl and HCl, which it was supposed were held together as the water of crystallisation is in salts. Even earlier than this (1857,Journal of the Petroffsky Academy) I considered similar cases as true compounds. In general, according to the law of limits, an unsaturated hydrocarbon, or its derivative, on combining withrX2, gives a substance which is saturated or else approaching the limit. The investigations of Frankland with many organo-metallic compounds clearly showed the limit in the case of metallic compounds, which we shall constantly refer to later on.
[25]My article on this subject appeared in the Journal of the St. Petersburg Academy of Sciences in 1861. Up to that time, although many additive combinations with hydrocarbons and their derivatives were known, they had not been generalised, and were even continually quoted as cases of substitution. Thus the combination of ethylene, C2H4, with chlorine, Cl2, was often regarded as a formation of the products of the substitution of C2H5Cl and HCl, which it was supposed were held together as the water of crystallisation is in salts. Even earlier than this (1857,Journal of the Petroffsky Academy) I considered similar cases as true compounds. In general, according to the law of limits, an unsaturated hydrocarbon, or its derivative, on combining withrX2, gives a substance which is saturated or else approaching the limit. The investigations of Frankland with many organo-metallic compounds clearly showed the limit in the case of metallic compounds, which we shall constantly refer to later on.
[26]The conception of homology has been applied by Gerhardt to all organic compounds in his classical work, ‘Traité de Chimie Organique,’ finished in 1855 (4 vols.), in which he divided all organic compounds intofattyandaromatic, which is in principle still adhered to at the present time, although the latter are more often called benzene derivatives, on account of the fact that Kekulé, in his beautiful investigations on the structure of aromatic compounds, showed the presence in them all of the ‘benzene nucleus,’ C6H6.
[26]The conception of homology has been applied by Gerhardt to all organic compounds in his classical work, ‘Traité de Chimie Organique,’ finished in 1855 (4 vols.), in which he divided all organic compounds intofattyandaromatic, which is in principle still adhered to at the present time, although the latter are more often called benzene derivatives, on account of the fact that Kekulé, in his beautiful investigations on the structure of aromatic compounds, showed the presence in them all of the ‘benzene nucleus,’ C6H6.
[27]This is always true for hydrocarbons, but for derivatives of the lower homologues the law is sometimes different; for instance, in the series of saturated alcohols, CnH2n+1(OH), whenn= 0, we obtain water, H(OH), which boils at 100°, and whose specific gravity at 15° = 0·9992; whenn= 1, wood spirit CH3(OH), which boils at 66°, and at 15° has a specific gravity = 0·7964; whenn= 2, ordinary alcohol, C2H5(OH), boiling at 78°, specific gravity at 15° = 0·7936, and with further increase of CH2the specific gravity increases. For the glycols CnH2n(OH)2the phenomenon of a similar kind is still more striking; at first the temperature of the boiling point and the density increase, and then for higher (more complex) members of the series diminish. The reason for this phenomenon, it is evident, must be sought for in the influence and properties of water, and that strong affinity which, acting between hydrogen and oxygen, determines many of the exceptional properties of water (ChapterI.).
[27]This is always true for hydrocarbons, but for derivatives of the lower homologues the law is sometimes different; for instance, in the series of saturated alcohols, CnH2n+1(OH), whenn= 0, we obtain water, H(OH), which boils at 100°, and whose specific gravity at 15° = 0·9992; whenn= 1, wood spirit CH3(OH), which boils at 66°, and at 15° has a specific gravity = 0·7964; whenn= 2, ordinary alcohol, C2H5(OH), boiling at 78°, specific gravity at 15° = 0·7936, and with further increase of CH2the specific gravity increases. For the glycols CnH2n(OH)2the phenomenon of a similar kind is still more striking; at first the temperature of the boiling point and the density increase, and then for higher (more complex) members of the series diminish. The reason for this phenomenon, it is evident, must be sought for in the influence and properties of water, and that strong affinity which, acting between hydrogen and oxygen, determines many of the exceptional properties of water (ChapterI.).
[28]As, for example, in the saturated series of hydrocarbons CnH2n+2, the lowest member (n= 0) must be taken as hydrogen H2, a gas which (t.c.below -190°) is liquefied with great difficulty, and when in a liquid state has doubtless a very small density. Wheren= 1, 2, 3, the hydrocarbons CH4, C2H6, C3H8are gases, more and more readily liquefiable. The temperature of the absolute boiling point for CH4= -100°, and for ethane C2H6, and in the higher members it rises. The hydrocarbon C4H10, liquefies at about 0°. C5H12(there are several isomers) boils at from +9° (Lvoff) to 37°, C6H14from 58° to 78°, &c. The specific gravities in a liquid state at 15° are:—C5H12C6H14C7H16C10H22C16H340·630·660·700·750·85
[28]As, for example, in the saturated series of hydrocarbons CnH2n+2, the lowest member (n= 0) must be taken as hydrogen H2, a gas which (t.c.below -190°) is liquefied with great difficulty, and when in a liquid state has doubtless a very small density. Wheren= 1, 2, 3, the hydrocarbons CH4, C2H6, C3H8are gases, more and more readily liquefiable. The temperature of the absolute boiling point for CH4= -100°, and for ethane C2H6, and in the higher members it rises. The hydrocarbon C4H10, liquefies at about 0°. C5H12(there are several isomers) boils at from +9° (Lvoff) to 37°, C6H14from 58° to 78°, &c. The specific gravities in a liquid state at 15° are:—
[29]If, at the ordinary temperature (assuming therefore that the water formed will be in a liquid state) a gram molecule (26 grams) of acetylene, C2H2, be burnt, 310 thousand calories will be emitted (Thomsen), and as 12 grams of charcoal produce 97 thousand calories, and 2 grams of hydrogen 69 thousand calories, it follows that, if the hydrogen and carbon of the acetylene were burnt there would be only 2 × 97 + 69, or 263 thousand calories produced. It is evident, then, that acetylene in its formation absorbs 310–263, or 47 thousand calories.For considerations relative to the combustion of carbon compounds, we will first enumerate the quantity of heat separated by the combustion of definite chemical carbon compounds, and then give a few figures bearing on the kinds of fuel used in practice.For molecular quantities in perfect combustion the following amounts of heat are given out (when gaseous carbonic anhydride and liquid water are formed), according to Thomsen's data (1) for gaseous CnH2n+2: 52·8 + 158·8nthousand calories; (2) for CnH2n: 17·7 + 158·1nthousand calories; (3) according to Stohmann (1888) for liquid saturated alcohols, CnH2n+2O: 11·8 + 156·3n, and as the latent heat of evaporation = about 8·2 + 0·6n, in a gaseous state, 20·0 + 156·9n; (4) for monobasic saturated liquid acids, CnH2nO2:—95·3 + 154·3n, and as their latent heat of evaporation is about 5·0 + 1·2n, in a gaseous form, about—90 + 155n; (5) for solid saturated bibasic acids, CnH2n-2O4:—253·8 + 152·6n, if they are expressed as CnH2nC2H2O4, then 51·4 + 152·6n; (6) for benzene and its liquid homologues (still according to Stohmann) CnH2n-6:—158·6 + 156·3n, and in a gaseous form about—155 + 157n; (7) for the gaseous homologues of acetylene, CnH2n-2(according to Thomsen)—5 + 157n. It is evident from the preceding figures that the group CH2, or CH3substituted for H, on burning gives out from 152 to 159 thousand calories. This is less than that given out by C + H2, which is 97 + 69 or 166 thousand; the reason for this difference (it would be still greater if carbon were gaseous) is the amount of heat separated during the formation of CH2. According to Stohmann, for dextroglucose, C6H12O6, it is 673·7; for common sugar, C12H22O11, 1325·7; for cellulose, C6H10O5, 678·0; starch, 677·5; dextrin, 666·2; glycol, C2H6O2, 281·7; glycerine, 397·2, &c. The heat of combustion of the following solids (determined by Stohmann) is expressed per unit of weight: naphthalene, C10H8, 9,621; urea, CN2H4O, 2,465; white of egg, 5,579; dry rye bread, 4,421; wheaten bread, 4,302; tallow, 9,365; butter, 9,192; linseed oil, 9,323. The most complete collection of arithmetical data for the heats of combustion will be found in V. F. Longinin's work, ‘Description of the Various Methods of Determining the Heats of Combustion of Organic Compounds’ (Moscow, 1894).The number of units of heat given out byunit weightduring the complete combustion and cooling of the following ordinary kinds of fuel in their usual state of dryness and purity are:—(1) for wood charcoal, anthracite, semi-anthracite, bituminous coal and coke, from 7,200 to 8,200; (2) dry, long flaming coals, and the best brown coals, from 6,200 to 6,800; (3) perfectly dry wood, 3,500; hardly dry, 2,500; (4) perfectly dry peat, best kind, 4,500; compressed and dried, 3,000; (5) petroleum refuse and similar liquid hydrocarbons, about 11,000; (6) illuminating gas of the ordinary composition (about 45 vols. H, 40 vols. CH4, 5 vols. CO, and 5 vols. N), about 12,000; (7) producer gas (seenext Chapter), containing 2 vols. carbonic anhydride, 30 vols. carbonic oxide, and 68 vols. nitrogenfor one part by weight of the whole carbon burnt, 5,300, and for one part by weight of the gas, 910, units of heat; and (8) water gas (seenext chapter) containing 4 vols. carbonic anhydride, 8 vols. N2, 24 vols. carbonic oxide, and 46 vols. H2, for one part by weight of the carbon consumed in thegenerator10,900, and for one part by weight of the gas, 3,600 units of heat. In these figures, as in all calorimetric observations, the water produced by the combustion of the fuel is supposed to be liquid. As regards the temperature reached by the fuel, it is important to remark that for solid fuel it is indispensable to admit (to ensure complete combustion) twice the amount of air required, but liquid, or pulverised fuel, and especially gaseous fuel, does not require an excess of air; therefore, a kilogram of charcoal, giving 8,000 units of heat, requires about 24 kilograms of air (3 kilograms of air per thousand calories) and a kilogram of producer gas requires only 0·77 kilogram of air (0·85 kilo. of air per 1,000 calories), 1 kilogram of water gas about 4·5 of air (1·25 kilo. of air per 1,000 calories).
[29]If, at the ordinary temperature (assuming therefore that the water formed will be in a liquid state) a gram molecule (26 grams) of acetylene, C2H2, be burnt, 310 thousand calories will be emitted (Thomsen), and as 12 grams of charcoal produce 97 thousand calories, and 2 grams of hydrogen 69 thousand calories, it follows that, if the hydrogen and carbon of the acetylene were burnt there would be only 2 × 97 + 69, or 263 thousand calories produced. It is evident, then, that acetylene in its formation absorbs 310–263, or 47 thousand calories.
For considerations relative to the combustion of carbon compounds, we will first enumerate the quantity of heat separated by the combustion of definite chemical carbon compounds, and then give a few figures bearing on the kinds of fuel used in practice.
For molecular quantities in perfect combustion the following amounts of heat are given out (when gaseous carbonic anhydride and liquid water are formed), according to Thomsen's data (1) for gaseous CnH2n+2: 52·8 + 158·8nthousand calories; (2) for CnH2n: 17·7 + 158·1nthousand calories; (3) according to Stohmann (1888) for liquid saturated alcohols, CnH2n+2O: 11·8 + 156·3n, and as the latent heat of evaporation = about 8·2 + 0·6n, in a gaseous state, 20·0 + 156·9n; (4) for monobasic saturated liquid acids, CnH2nO2:—95·3 + 154·3n, and as their latent heat of evaporation is about 5·0 + 1·2n, in a gaseous form, about—90 + 155n; (5) for solid saturated bibasic acids, CnH2n-2O4:—253·8 + 152·6n, if they are expressed as CnH2nC2H2O4, then 51·4 + 152·6n; (6) for benzene and its liquid homologues (still according to Stohmann) CnH2n-6:—158·6 + 156·3n, and in a gaseous form about—155 + 157n; (7) for the gaseous homologues of acetylene, CnH2n-2(according to Thomsen)—5 + 157n. It is evident from the preceding figures that the group CH2, or CH3substituted for H, on burning gives out from 152 to 159 thousand calories. This is less than that given out by C + H2, which is 97 + 69 or 166 thousand; the reason for this difference (it would be still greater if carbon were gaseous) is the amount of heat separated during the formation of CH2. According to Stohmann, for dextroglucose, C6H12O6, it is 673·7; for common sugar, C12H22O11, 1325·7; for cellulose, C6H10O5, 678·0; starch, 677·5; dextrin, 666·2; glycol, C2H6O2, 281·7; glycerine, 397·2, &c. The heat of combustion of the following solids (determined by Stohmann) is expressed per unit of weight: naphthalene, C10H8, 9,621; urea, CN2H4O, 2,465; white of egg, 5,579; dry rye bread, 4,421; wheaten bread, 4,302; tallow, 9,365; butter, 9,192; linseed oil, 9,323. The most complete collection of arithmetical data for the heats of combustion will be found in V. F. Longinin's work, ‘Description of the Various Methods of Determining the Heats of Combustion of Organic Compounds’ (Moscow, 1894).
The number of units of heat given out byunit weightduring the complete combustion and cooling of the following ordinary kinds of fuel in their usual state of dryness and purity are:—(1) for wood charcoal, anthracite, semi-anthracite, bituminous coal and coke, from 7,200 to 8,200; (2) dry, long flaming coals, and the best brown coals, from 6,200 to 6,800; (3) perfectly dry wood, 3,500; hardly dry, 2,500; (4) perfectly dry peat, best kind, 4,500; compressed and dried, 3,000; (5) petroleum refuse and similar liquid hydrocarbons, about 11,000; (6) illuminating gas of the ordinary composition (about 45 vols. H, 40 vols. CH4, 5 vols. CO, and 5 vols. N), about 12,000; (7) producer gas (seenext Chapter), containing 2 vols. carbonic anhydride, 30 vols. carbonic oxide, and 68 vols. nitrogenfor one part by weight of the whole carbon burnt, 5,300, and for one part by weight of the gas, 910, units of heat; and (8) water gas (seenext chapter) containing 4 vols. carbonic anhydride, 8 vols. N2, 24 vols. carbonic oxide, and 46 vols. H2, for one part by weight of the carbon consumed in thegenerator10,900, and for one part by weight of the gas, 3,600 units of heat. In these figures, as in all calorimetric observations, the water produced by the combustion of the fuel is supposed to be liquid. As regards the temperature reached by the fuel, it is important to remark that for solid fuel it is indispensable to admit (to ensure complete combustion) twice the amount of air required, but liquid, or pulverised fuel, and especially gaseous fuel, does not require an excess of air; therefore, a kilogram of charcoal, giving 8,000 units of heat, requires about 24 kilograms of air (3 kilograms of air per thousand calories) and a kilogram of producer gas requires only 0·77 kilogram of air (0·85 kilo. of air per 1,000 calories), 1 kilogram of water gas about 4·5 of air (1·25 kilo. of air per 1,000 calories).
[29 bis]Manure which decomposes under the action of bacteria gives off CO2and CH4.
[29 bis]Manure which decomposes under the action of bacteria gives off CO2and CH4.
[30]It is easy to collect the gas which is evolved in marshy places if a glass bottle be inverted in the water and a funnel put into it (both filled with water); if the mud of the bottom be now agitated, the bubbles which rise may be easily caught by the inverted funnel.
[30]It is easy to collect the gas which is evolved in marshy places if a glass bottle be inverted in the water and a funnel put into it (both filled with water); if the mud of the bottom be now agitated, the bubbles which rise may be easily caught by the inverted funnel.
[31]see captionFig.58.—General view of gas works.B, retorts;f, hydraulic main;HandI, tar well;i, condensers;L, purifiers;P, gasholder.see captionFig.59.—Blowpipe. Air is blown in at the trumpet-shaped mouthpiece, and escapes in a fine stream from the platinum jet placed at the extremity of the side tube.see captionFig.60.—Davy safety-lamp. [Modern form.]Illuminating gas is generally prepared by heating gas coal (seeNote6) in oval cylindrical horizontal cast-iron or clay retorts. Several such retortsBB(fig.58) are disposed in the furnaceA, and heated together. When the retorts are heated to a red heat, lumps of coal are thrown into them, and they are then closed with a closely fitting cover. The illustration shows the furnace, with five retorts. Coke (seeNote1, dry distillation) remains in the retorts, and the volatile products in the form of vapours and gases travel along the piped, rising from each retort. These pipes branch above the stove, and communicate with the receiverf(hydraulic main) placed above the furnace. Those products of the dry distillation which most easily pass from the gaseous into the liquid and solid states collect in the hydraulic main. From the hydraulic main the vapours and gases travel along the pipegand the series of vertical pipesj(which are sometimes cooled by water trickling over the surface), where the vapours and gases cool from the contact of the colder surface, and a fresh quantity of vapour condenses. The condensed liquids pass from the pipesgandjand into the troughsH. These troughs always contain liquid at a constant level (the excess flowing away) so that the gas cannot escape, and thus they form, as it is termed, a hydraulic joint. In the state in which it leaves the condensers the gas consists principally of the following vapours and gases: (1) vapour of water, (2) ammonium carbonate, (3) liquid hydrocarbons, (4) hydrogen sulphide, H2S, (5) carbonic anhydride, CO2, (6) carbonic oxide, CO, (7) sulphurous anhydride, SO2, but a great part of the illuminating gas consists of (8) hydrogen, (9) marsh gas, (10) olefiant gas, C2H4, and other gaseous hydrocarbons. The hydrocarbons (3, 9, and 10), the hydrogen, and carbonic oxide are capable of combustion, and are useful component parts, but the carbonic anhydride, the hydrogen sulphide, and sulphurous anhydride, as well as the vapours of ammonium carbonate, form an injurious admixture, because they do not burn (CO2, SO2) and lower the temperature and brilliancy of the flame, or else, although capable of burning (for example, H2S, CS2, and others), they give out during combustion sulphurous anhydride which has a disagreeable smell, is injurious when inhaled, and spoils many surrounding objects. In order to separate the injurious products, the gas is washed with water, a cylinder (not shown in the illustration) filled with coke continually moistened with water serving for this purpose. The water coming into contact with the gas dissolves the ammonium carbonate; hydrogen sulphide, carbonic anhydride, and sulphurous anhydride, being only partly soluble in water, have to be got rid of by a special means. For this purpose the gas is passed through moist lime or other alkaline liquid, as the above-mentioned gases have acid properties and are therefore retained by the alkali. In the case of lime, calcium carbonate, sulphite and sulphide, all solid substances, are formed. It is necessary to renew the purifying material as its absorbing power decreases. A mixture of lime and sulphate of iron, FeSO4, acts still better, because the latter, with lime, Ca(HO)2, forms ferrous hydroxide, Fe(HO)2and gypsum, CaSO4. The suboxide (partly turning into oxide) of iron absorbs H2S, forming FeS and H2O, and the gypsum retains the remainder of the ammonia, the excess of lime absorbing carbonic anhydride and sulphuric anhydride. [In English works a native hydrated ferric hydroxide is used for removing hydrogen sulphide.] This purification of the gas takes place in the apparatusL, where the gas passes through perforated traysm, covered with sawdust mixed with lime and sulphate of iron. It is necessary to remark that in the manufacture of gas it is indispensable to draw off the vapours from the retorts, so that they should not remain there long (otherwise the hydrocarbons would in a considerable degree be resolved into charcoal and hydrogen), and also to avoid a great pressure of gas in the apparatus, otherwise a quantity of gas would escape at all cracks such as must inevitably exist in such a complicated arrangement. For this purpose there are special pumps (exhausters) so regulated that they only pump off the quantity of gas formed (the pump is not shown in the illustration). The purified gas passes through the pipeninto the gasometer (gasholder)P, a dome made of iron plate. The edges of the dome dip into water poured into a ring-shaped channelg, in which the sides of the dome rise and fall. The gas is collected in this holder, and distributed to its destination by pipes communicating with the pipeo, issuing from the dome. The pressure of the dome on the gas enables it, on issuing from a long pipe, to penetrate through the small aperture of the burner. A hundred kilograms of coal give about 20 to 30 cubic metres of gas, having a density from four to nine times greater than that of hydrogen. A cubic metre (1,000 litres) of hydrogen weighs about 87 grams; therefore 100 kilograms of coal give about 18 kilograms of gas, or about one-sixth of its weight. Illuminating gas is generally lighter than marsh gas, as it contains a considerable amount of hydrogen, and is only heavier than marsh gas when it contains much of the heavier hydrocarbons. Thus olefiant gas, C2H4, is fourteen times, and the vapours of benzene thirty-nine times, heavier than hydrogen, and illuminating gas sometimes contains 15 p.c. of its volume of them. The brilliancy of the flame of the gas increases with the quantity of olefiant gas and similar heavy hydrocarbons, as it then contains more carbon for a given volume and a greater number of carbon particles are separated. Gas usually contains from 35 to 60 p.c. of its volume of marsh gas, from 30 to 50 p.c. of hydrogen, from 3 to 5 p.c. of carbonic oxide, from 2 to 10 p.c. heavy hydrocarbons, and from 3 to 10 p.c. of nitrogen. Wood gives almost the same sort of gas as coal and almost the same quantity, but the wood gas contains a great deal of carbonic anhydride, although on the other hand there is an almost complete absence of sulphur compounds. Tar, oils, naphtha, and such materials furnish a large quantity of good illuminating gas. An ordinary burner of 8 to 12 candle-power burns 5 to 6 cubic feet of coal gas per hour, but only 1 cubic foot of naphtha gas. One pood (36 lbs. Eng.) of naphtha gives 500 cubic feet of gas—that is, one kilogram of naphtha produces about one cubic metre of gas. The formation of combustible gas by heating coal was discovered in the beginning of the last century, but only put into practice towards the end by Le-Bon in France and Murdoch in England. In England, Murdoch, together with the renowned Watt, built the first gas works in 1805.In practice illuminating gas is not only used for lighting (electricity and kerosene are cheaper in Russia), but also as the motive power for gas engines (seep.175), which consume about half a cubic metre per horse-power per hour; gas is also used in laboratories for heating purposes. When it is necessary to concentrate the heat, either the ordinary blowpipe (fig.59) is applied, placing the end in the flame and blowing through the mouthpiece; or, in other forms, gas is passed through the blowpipe; when a large, hot, smokeless flame is required for heating crucibles or glass-blowing, a foot-blower is used. High temperatures, which are often required for laboratory and manufacturing purposes, are most easily attained by the use of gaseous fuel (illuminating gas, producer gas, and water gas, which will be treated of in thefollowing chapter), because complete combustion may be effected without an access of air. It is evident that in order to obtain high temperatures means must be taken to diminish the loss of heat by radiation, and to ensure perfect combustion.
[31]
see captionFig.58.—General view of gas works.B, retorts;f, hydraulic main;HandI, tar well;i, condensers;L, purifiers;P, gasholder.
Fig.58.—General view of gas works.B, retorts;f, hydraulic main;HandI, tar well;i, condensers;L, purifiers;P, gasholder.
see captionFig.59.—Blowpipe. Air is blown in at the trumpet-shaped mouthpiece, and escapes in a fine stream from the platinum jet placed at the extremity of the side tube.
Fig.59.—Blowpipe. Air is blown in at the trumpet-shaped mouthpiece, and escapes in a fine stream from the platinum jet placed at the extremity of the side tube.
see captionFig.60.—Davy safety-lamp. [Modern form.]
Fig.60.—Davy safety-lamp. [Modern form.]
Illuminating gas is generally prepared by heating gas coal (seeNote6) in oval cylindrical horizontal cast-iron or clay retorts. Several such retortsBB(fig.58) are disposed in the furnaceA, and heated together. When the retorts are heated to a red heat, lumps of coal are thrown into them, and they are then closed with a closely fitting cover. The illustration shows the furnace, with five retorts. Coke (seeNote1, dry distillation) remains in the retorts, and the volatile products in the form of vapours and gases travel along the piped, rising from each retort. These pipes branch above the stove, and communicate with the receiverf(hydraulic main) placed above the furnace. Those products of the dry distillation which most easily pass from the gaseous into the liquid and solid states collect in the hydraulic main. From the hydraulic main the vapours and gases travel along the pipegand the series of vertical pipesj(which are sometimes cooled by water trickling over the surface), where the vapours and gases cool from the contact of the colder surface, and a fresh quantity of vapour condenses. The condensed liquids pass from the pipesgandjand into the troughsH. These troughs always contain liquid at a constant level (the excess flowing away) so that the gas cannot escape, and thus they form, as it is termed, a hydraulic joint. In the state in which it leaves the condensers the gas consists principally of the following vapours and gases: (1) vapour of water, (2) ammonium carbonate, (3) liquid hydrocarbons, (4) hydrogen sulphide, H2S, (5) carbonic anhydride, CO2, (6) carbonic oxide, CO, (7) sulphurous anhydride, SO2, but a great part of the illuminating gas consists of (8) hydrogen, (9) marsh gas, (10) olefiant gas, C2H4, and other gaseous hydrocarbons. The hydrocarbons (3, 9, and 10), the hydrogen, and carbonic oxide are capable of combustion, and are useful component parts, but the carbonic anhydride, the hydrogen sulphide, and sulphurous anhydride, as well as the vapours of ammonium carbonate, form an injurious admixture, because they do not burn (CO2, SO2) and lower the temperature and brilliancy of the flame, or else, although capable of burning (for example, H2S, CS2, and others), they give out during combustion sulphurous anhydride which has a disagreeable smell, is injurious when inhaled, and spoils many surrounding objects. In order to separate the injurious products, the gas is washed with water, a cylinder (not shown in the illustration) filled with coke continually moistened with water serving for this purpose. The water coming into contact with the gas dissolves the ammonium carbonate; hydrogen sulphide, carbonic anhydride, and sulphurous anhydride, being only partly soluble in water, have to be got rid of by a special means. For this purpose the gas is passed through moist lime or other alkaline liquid, as the above-mentioned gases have acid properties and are therefore retained by the alkali. In the case of lime, calcium carbonate, sulphite and sulphide, all solid substances, are formed. It is necessary to renew the purifying material as its absorbing power decreases. A mixture of lime and sulphate of iron, FeSO4, acts still better, because the latter, with lime, Ca(HO)2, forms ferrous hydroxide, Fe(HO)2and gypsum, CaSO4. The suboxide (partly turning into oxide) of iron absorbs H2S, forming FeS and H2O, and the gypsum retains the remainder of the ammonia, the excess of lime absorbing carbonic anhydride and sulphuric anhydride. [In English works a native hydrated ferric hydroxide is used for removing hydrogen sulphide.] This purification of the gas takes place in the apparatusL, where the gas passes through perforated traysm, covered with sawdust mixed with lime and sulphate of iron. It is necessary to remark that in the manufacture of gas it is indispensable to draw off the vapours from the retorts, so that they should not remain there long (otherwise the hydrocarbons would in a considerable degree be resolved into charcoal and hydrogen), and also to avoid a great pressure of gas in the apparatus, otherwise a quantity of gas would escape at all cracks such as must inevitably exist in such a complicated arrangement. For this purpose there are special pumps (exhausters) so regulated that they only pump off the quantity of gas formed (the pump is not shown in the illustration). The purified gas passes through the pipeninto the gasometer (gasholder)P, a dome made of iron plate. The edges of the dome dip into water poured into a ring-shaped channelg, in which the sides of the dome rise and fall. The gas is collected in this holder, and distributed to its destination by pipes communicating with the pipeo, issuing from the dome. The pressure of the dome on the gas enables it, on issuing from a long pipe, to penetrate through the small aperture of the burner. A hundred kilograms of coal give about 20 to 30 cubic metres of gas, having a density from four to nine times greater than that of hydrogen. A cubic metre (1,000 litres) of hydrogen weighs about 87 grams; therefore 100 kilograms of coal give about 18 kilograms of gas, or about one-sixth of its weight. Illuminating gas is generally lighter than marsh gas, as it contains a considerable amount of hydrogen, and is only heavier than marsh gas when it contains much of the heavier hydrocarbons. Thus olefiant gas, C2H4, is fourteen times, and the vapours of benzene thirty-nine times, heavier than hydrogen, and illuminating gas sometimes contains 15 p.c. of its volume of them. The brilliancy of the flame of the gas increases with the quantity of olefiant gas and similar heavy hydrocarbons, as it then contains more carbon for a given volume and a greater number of carbon particles are separated. Gas usually contains from 35 to 60 p.c. of its volume of marsh gas, from 30 to 50 p.c. of hydrogen, from 3 to 5 p.c. of carbonic oxide, from 2 to 10 p.c. heavy hydrocarbons, and from 3 to 10 p.c. of nitrogen. Wood gives almost the same sort of gas as coal and almost the same quantity, but the wood gas contains a great deal of carbonic anhydride, although on the other hand there is an almost complete absence of sulphur compounds. Tar, oils, naphtha, and such materials furnish a large quantity of good illuminating gas. An ordinary burner of 8 to 12 candle-power burns 5 to 6 cubic feet of coal gas per hour, but only 1 cubic foot of naphtha gas. One pood (36 lbs. Eng.) of naphtha gives 500 cubic feet of gas—that is, one kilogram of naphtha produces about one cubic metre of gas. The formation of combustible gas by heating coal was discovered in the beginning of the last century, but only put into practice towards the end by Le-Bon in France and Murdoch in England. In England, Murdoch, together with the renowned Watt, built the first gas works in 1805.
In practice illuminating gas is not only used for lighting (electricity and kerosene are cheaper in Russia), but also as the motive power for gas engines (seep.175), which consume about half a cubic metre per horse-power per hour; gas is also used in laboratories for heating purposes. When it is necessary to concentrate the heat, either the ordinary blowpipe (fig.59) is applied, placing the end in the flame and blowing through the mouthpiece; or, in other forms, gas is passed through the blowpipe; when a large, hot, smokeless flame is required for heating crucibles or glass-blowing, a foot-blower is used. High temperatures, which are often required for laboratory and manufacturing purposes, are most easily attained by the use of gaseous fuel (illuminating gas, producer gas, and water gas, which will be treated of in thefollowing chapter), because complete combustion may be effected without an access of air. It is evident that in order to obtain high temperatures means must be taken to diminish the loss of heat by radiation, and to ensure perfect combustion.
[32]The gas which is set free in coal mines contains a good deal of nitrogen, some carbonic anhydride, and a large quantity of marsh gas. The best means of avoiding an explosion consists in efficient ventilation. It is best to light coal mines with electric lamps.
[32]The gas which is set free in coal mines contains a good deal of nitrogen, some carbonic anhydride, and a large quantity of marsh gas. The best means of avoiding an explosion consists in efficient ventilation. It is best to light coal mines with electric lamps.
[33]The Davy lamp, of which an improved form is represented in the accompanying figure, is used for lighting coal and other mines where combustible gas is found. The wick of the lamp is enclosed in a thick glass cylinder which is firmly held in a metallic holder. Over this a metallic cylinder and the wire gauze are placed. The products of combustion pass through the gauze, and the air enters through the space between the cylinder and the wire gauze. To ensure greater safety the lamp cannot be opened without extinguishing the flame.
[33]The Davy lamp, of which an improved form is represented in the accompanying figure, is used for lighting coal and other mines where combustible gas is found. The wick of the lamp is enclosed in a thick glass cylinder which is firmly held in a metallic holder. Over this a metallic cylinder and the wire gauze are placed. The products of combustion pass through the gauze, and the air enters through the space between the cylinder and the wire gauze. To ensure greater safety the lamp cannot be opened without extinguishing the flame.
[34]In Pennsylvania (beyond the Alleghany mountains) many of the shafts sunk for petroleum only emitted gas, but many useful applications for it were found and it was conducted in metallic pipes to works hundreds of miles distant, principally for metallurgical purposes.
[34]In Pennsylvania (beyond the Alleghany mountains) many of the shafts sunk for petroleum only emitted gas, but many useful applications for it were found and it was conducted in metallic pipes to works hundreds of miles distant, principally for metallurgical purposes.
[35]The purest gas is prepared by mixing the liquid substance called zinc methyl, Zn(CH3)2, with water, when the following reaction occurs:Zn(CH3)2+ 2HOH = Zn(HO)2+ 2CH3H.
[35]The purest gas is prepared by mixing the liquid substance called zinc methyl, Zn(CH3)2, with water, when the following reaction occurs:
Zn(CH3)2+ 2HOH = Zn(HO)2+ 2CH3H.
[36]Methylene, CH2, does not exist. When attempts are made to obtain it (for example, by removing X2from CH2X2), C2H4or C3H6are produced—that is to say, it undergoes polymerisation.
[36]Methylene, CH2, does not exist. When attempts are made to obtain it (for example, by removing X2from CH2X2), C2H4or C3H6are produced—that is to say, it undergoes polymerisation.
[37]Although the methods of formation and the reactions connected with hydrocarbons are not described in this work, because they are dealt with in organic chemistry, yet in order to clearly show the mechanism of those transformations by which the carbon atoms are built up into the molecules of the carbon compounds, we here give a general example of reactions of this kind. From marsh gas, CH4, on the one hand the substitution of chlorine or iodine, CH3Cl, CH3I, for the hydrogen may be effected, and on the other hand such metals as sodium may be substituted for the hydrogen,e.g.CH3Na. These and similar products of substitution serve as a means of obtaining other more complex substances from given carbon compounds. If we place the two above-named products of substitution of marsh gas (metallic and haloid) in mutual contact, the metal combines with the halogen, forming a very stable compound—namely, common salt, NaCl, and the carbon groups which were in combination with them separate in mutual combination, as shown by the equation:CH3Cl + CH3Na = NaCl + C2H6.This is the most simple example of the formation of a complex hydrocarbon from these radicles. The cause of the reaction must be sought for in the property which the haloid (chlorine) and sodium have of entering into mutual combination.
[37]Although the methods of formation and the reactions connected with hydrocarbons are not described in this work, because they are dealt with in organic chemistry, yet in order to clearly show the mechanism of those transformations by which the carbon atoms are built up into the molecules of the carbon compounds, we here give a general example of reactions of this kind. From marsh gas, CH4, on the one hand the substitution of chlorine or iodine, CH3Cl, CH3I, for the hydrogen may be effected, and on the other hand such metals as sodium may be substituted for the hydrogen,e.g.CH3Na. These and similar products of substitution serve as a means of obtaining other more complex substances from given carbon compounds. If we place the two above-named products of substitution of marsh gas (metallic and haloid) in mutual contact, the metal combines with the halogen, forming a very stable compound—namely, common salt, NaCl, and the carbon groups which were in combination with them separate in mutual combination, as shown by the equation:
CH3Cl + CH3Na = NaCl + C2H6.
This is the most simple example of the formation of a complex hydrocarbon from these radicles. The cause of the reaction must be sought for in the property which the haloid (chlorine) and sodium have of entering into mutual combination.
[38]Whenm=n- 1, we have the series CnH2. The lowest member is acetylene, C2H2. These are hydrocarbons containing a minimum amount of hydrogen.
[38]Whenm=n- 1, we have the series CnH2. The lowest member is acetylene, C2H2. These are hydrocarbons containing a minimum amount of hydrogen.
[39]For instance, ethylene, C2H4, combines with Br2, HI, H2SO4, as a whole molecule, as also does amylene, C5H10, and, in general, CnH2n.
[39]For instance, ethylene, C2H4, combines with Br2, HI, H2SO4, as a whole molecule, as also does amylene, C5H10, and, in general, CnH2n.
[40]For instance, ethylene is obtained by removing the water from ethyl alcohol, C2H5(OH), and amylene, C5H10, from amyl alcohol, C5H11(OH), or in general CnH2n, from CnH2n+1(OH).
[40]For instance, ethylene is obtained by removing the water from ethyl alcohol, C2H5(OH), and amylene, C5H10, from amyl alcohol, C5H11(OH), or in general CnH2n, from CnH2n+1(OH).
[41]Acetylene and its polymerides have an empirical composition CH, ethylene and its homologues (and polymerides) CH2, ethane CH3, methane CH4. This series presents a good example of the law of multiple proportions, but such diverse proportions are met with between the number of atoms of the carbon and hydrogen in the hydrocarbons already known that the accuracy of Dalton's law might be doubted. Thus the substances C30H62and C30H60differ so slightly in their composition by weight as to be within the limits of experimental error, but their reactions and properties are so distinct that they can be distinguished beyond a doubt. Without Dalton's law chemistry could not have been brought to its present condition, but it cannot alone express all those gradations which are quite clearly understood and predicted by the law of Avogadro-Gerhardt.
[41]Acetylene and its polymerides have an empirical composition CH, ethylene and its homologues (and polymerides) CH2, ethane CH3, methane CH4. This series presents a good example of the law of multiple proportions, but such diverse proportions are met with between the number of atoms of the carbon and hydrogen in the hydrocarbons already known that the accuracy of Dalton's law might be doubted. Thus the substances C30H62and C30H60differ so slightly in their composition by weight as to be within the limits of experimental error, but their reactions and properties are so distinct that they can be distinguished beyond a doubt. Without Dalton's law chemistry could not have been brought to its present condition, but it cannot alone express all those gradations which are quite clearly understood and predicted by the law of Avogadro-Gerhardt.
[42]The conception of the structure of carbon compounds—that is, the expression of those unions and correlations which their atoms have in the molecules—was for a long time limited to the representation that organic substances contained complex radicles (for instance, ethyl C2H5, methyl CH3, phenyl C6H5, &c.); then about the year 1840 the phenomena of substitution and the correspondence of the products of substitution with the primary bodies (nuclei and types) were observed, but it was not until about the year 1860 and later when on the one hand the teaching of Gerhardt about molecules was spreading, and on the other hand the materials had accumulated for discussing the transformations of the simplest hydrocarbon compounds, that conjectures began to appear as to the mutual connection of the atoms of carbon in the molecules of the complex hydrocarbon compounds. Then Kekulé and A. M. Butleroff began to formulate the connection between the separate atoms of carbon, regarding it as a quadrivalent element. Although in their methods of expression and in some of their views they differ from each other and also from the way in which the subject is treated in this work, yet the essence of the matter—namely, the comprehension of the causes of isomerism and of the union between the separate atoms of carbon—remains the same. In addition to this, starting from the year 1870, there appears a tendency which from year to year increases to discover the actual spacial distribution of the atoms in the molecules. Thanks to the endeavours of Le-Bel (1874), Van't Hoff (1874), and Wislicenus (1887) in observing cases of isomerism—such as the effect of different isomerides on the direction of the rotation of the plane of polarisation of light—this tendency promises much for chemical mechanics, but the details of the still imperfect knowledge in relation to this matter must be sought for in special works devoted to organic chemistry.
[42]The conception of the structure of carbon compounds—that is, the expression of those unions and correlations which their atoms have in the molecules—was for a long time limited to the representation that organic substances contained complex radicles (for instance, ethyl C2H5, methyl CH3, phenyl C6H5, &c.); then about the year 1840 the phenomena of substitution and the correspondence of the products of substitution with the primary bodies (nuclei and types) were observed, but it was not until about the year 1860 and later when on the one hand the teaching of Gerhardt about molecules was spreading, and on the other hand the materials had accumulated for discussing the transformations of the simplest hydrocarbon compounds, that conjectures began to appear as to the mutual connection of the atoms of carbon in the molecules of the complex hydrocarbon compounds. Then Kekulé and A. M. Butleroff began to formulate the connection between the separate atoms of carbon, regarding it as a quadrivalent element. Although in their methods of expression and in some of their views they differ from each other and also from the way in which the subject is treated in this work, yet the essence of the matter—namely, the comprehension of the causes of isomerism and of the union between the separate atoms of carbon—remains the same. In addition to this, starting from the year 1870, there appears a tendency which from year to year increases to discover the actual spacial distribution of the atoms in the molecules. Thanks to the endeavours of Le-Bel (1874), Van't Hoff (1874), and Wislicenus (1887) in observing cases of isomerism—such as the effect of different isomerides on the direction of the rotation of the plane of polarisation of light—this tendency promises much for chemical mechanics, but the details of the still imperfect knowledge in relation to this matter must be sought for in special works devoted to organic chemistry.
[43]Direct experiment shows that however CH3X is prepared (where X = for instance Cl, &c.) it is always one and the same substance. If, for example, in CX4, X is gradually replaced by hydrogen until CH3X is produced, or in CH4, the hydrogen by various means is replaced by X, or else, for instance, if CH3X be obtained by the decomposition of more complex compounds, the same product is always obtained.This was shown in the year 1860, or thereabout, by many methods, and is the fundamental conception of the structure of hydrocarbon compounds. If the atoms of hydrogen in methyl were not absolutely identical in value and position (as they are not, for instance, in CH3CH2CH3or CH3CH2X), then there would be as many different forms of CH3X as there were diversities in the atoms of hydrogen in CH4. The scope of this work does not permit of a more detailed account of this matter. It is given in works on organic chemistry.
[43]Direct experiment shows that however CH3X is prepared (where X = for instance Cl, &c.) it is always one and the same substance. If, for example, in CX4, X is gradually replaced by hydrogen until CH3X is produced, or in CH4, the hydrogen by various means is replaced by X, or else, for instance, if CH3X be obtained by the decomposition of more complex compounds, the same product is always obtained.
This was shown in the year 1860, or thereabout, by many methods, and is the fundamental conception of the structure of hydrocarbon compounds. If the atoms of hydrogen in methyl were not absolutely identical in value and position (as they are not, for instance, in CH3CH2CH3or CH3CH2X), then there would be as many different forms of CH3X as there were diversities in the atoms of hydrogen in CH4. The scope of this work does not permit of a more detailed account of this matter. It is given in works on organic chemistry.
[44]The union of carbon atoms in closed chains or rings was first suggested by Kekulé as an explanation of the structure and isomerism of the derivatives of benzene, C6H6, forming aromatic compounds (Note26).
[44]The union of carbon atoms in closed chains or rings was first suggested by Kekulé as an explanation of the structure and isomerism of the derivatives of benzene, C6H6, forming aromatic compounds (Note26).
[45]The following are the most generally known of the oxygenised but non-nitrogenous hydrocarbon derivatives. (1) the alcohols. These are hydrocarbons in which hydrogen is exchanged for hydroxyl (OH). The simplest of these is methyl alcohol, CH3(OH), or wood spirit obtained by the dry distillation of wood. The common spirits of wine or ethyl alcohol, C2H3(OH), and glycol, C2H4(OH)2, correspond with ethane. Normal propyl alcohol, CH3CH2CH2(OH), and isopropyl alcohol, CH3CH(OH)CH3, propylene-glycol, C3H6(OH)2, and glycerol, C3H3(OH)3(which, with stearic and other acids, forms fatty substances), correspond with propane, C3H8. All alcohols are capable of forming water and ethereal salts with acids, just as alkalis form ordinary salts. (2) Aldehydes are alcohols minus hydrogen; for instance, acetaldehyde, C2H4O, corresponds with ethyl alcohol. (3) It is simplest to regard organic acids as hydrocarbons in which hydrogen has been exchanged for carboxyl (CO2H), as will be explained in thefollowing chapter. There are a number of intermediate compounds; for example, the aldehyde-alcohols, alcohol-acids (or hydroxy-acids), &c. Thus the hydroxy-acids are hydrocarbons in which some of the hydrogen has been replaced by hydroxyl, and some by carboxyl; for instance, lactic acid corresponds with C2H6, and has the constitution C2H4(OH)(CO2H). If to these products we add the haloid salts (where H is replaced by Cl, Br, I), the nitro-compounds containing NO2in place of H, the amides, cyanides, ketones, and other compounds, it will be readily seen what an immense number of organic compounds there are and what a variety of properties these substances have; this we see also from the composition of plants and animals.
[45]The following are the most generally known of the oxygenised but non-nitrogenous hydrocarbon derivatives. (1) the alcohols. These are hydrocarbons in which hydrogen is exchanged for hydroxyl (OH). The simplest of these is methyl alcohol, CH3(OH), or wood spirit obtained by the dry distillation of wood. The common spirits of wine or ethyl alcohol, C2H3(OH), and glycol, C2H4(OH)2, correspond with ethane. Normal propyl alcohol, CH3CH2CH2(OH), and isopropyl alcohol, CH3CH(OH)CH3, propylene-glycol, C3H6(OH)2, and glycerol, C3H3(OH)3(which, with stearic and other acids, forms fatty substances), correspond with propane, C3H8. All alcohols are capable of forming water and ethereal salts with acids, just as alkalis form ordinary salts. (2) Aldehydes are alcohols minus hydrogen; for instance, acetaldehyde, C2H4O, corresponds with ethyl alcohol. (3) It is simplest to regard organic acids as hydrocarbons in which hydrogen has been exchanged for carboxyl (CO2H), as will be explained in thefollowing chapter. There are a number of intermediate compounds; for example, the aldehyde-alcohols, alcohol-acids (or hydroxy-acids), &c. Thus the hydroxy-acids are hydrocarbons in which some of the hydrogen has been replaced by hydroxyl, and some by carboxyl; for instance, lactic acid corresponds with C2H6, and has the constitution C2H4(OH)(CO2H). If to these products we add the haloid salts (where H is replaced by Cl, Br, I), the nitro-compounds containing NO2in place of H, the amides, cyanides, ketones, and other compounds, it will be readily seen what an immense number of organic compounds there are and what a variety of properties these substances have; this we see also from the composition of plants and animals.
[46]Ethylene bromide, C2H4Br2, when gently heated in alcoholic solution with finely divided zinc, yields pure ethylene, the zinc merely taking up the bromine (Sabaneyeff).
[46]Ethylene bromide, C2H4Br2, when gently heated in alcoholic solution with finely divided zinc, yields pure ethylene, the zinc merely taking up the bromine (Sabaneyeff).
[47]Ethylene decomposes somewhat easily under the influence of the electric spark, or a high temperature. In this case the volume of the gas formed may remain the same when olefiant gas is decomposed into carbon and marsh gas, or may increase to double its volume when hydrogen and carbon are formed, C2H4= CH4+ C = 2C + 2H2. A mixture of olefiant gas and oxygen is highly explosive; two volumes of this gas require six volumes of oxygen for its perfect combustion. The eight volumes thus taken then resolve themselves into eight volumes of the products of combustion, a mixture of water and carbonic anhydride, C2H4+ 3O2= 2CO2+ 2H2O. On cooling after the explosion diminution of volume occurs because the water becomes liquid. For two volumes of the olefiant gas taken, the diminution will be equal to four volumes, and the same for marsh gas. The quantity of carbonic anhydride formed by both gases is not the same. Two volumes of marsh gas give only two volumes of carbonic anhydride, and two volumes of ethylene give four volumes of carbonic anhydride.
[47]Ethylene decomposes somewhat easily under the influence of the electric spark, or a high temperature. In this case the volume of the gas formed may remain the same when olefiant gas is decomposed into carbon and marsh gas, or may increase to double its volume when hydrogen and carbon are formed, C2H4= CH4+ C = 2C + 2H2. A mixture of olefiant gas and oxygen is highly explosive; two volumes of this gas require six volumes of oxygen for its perfect combustion. The eight volumes thus taken then resolve themselves into eight volumes of the products of combustion, a mixture of water and carbonic anhydride, C2H4+ 3O2= 2CO2+ 2H2O. On cooling after the explosion diminution of volume occurs because the water becomes liquid. For two volumes of the olefiant gas taken, the diminution will be equal to four volumes, and the same for marsh gas. The quantity of carbonic anhydride formed by both gases is not the same. Two volumes of marsh gas give only two volumes of carbonic anhydride, and two volumes of ethylene give four volumes of carbonic anhydride.
[48]The homologues of ethylene, CnH2n, are also capable of direct combination with halogens, &c., but with various degrees of facility. The composition of these homologues can be expressed thus: (CH3)_x(CH2)y(CH)zCr, where the sum ofx+zis always an even number, and the sum ofx+z+ris equal to half the sum of 3x+z, whencez+ 2r=x; by this means the possible isomerides are determined. For example, for butylenes, C4H8, (CH3)2(CH)2, (CH3)2(CH2)C, (CH2)(CH2)2CH, and (CH2)4are possible.
[48]The homologues of ethylene, CnH2n, are also capable of direct combination with halogens, &c., but with various degrees of facility. The composition of these homologues can be expressed thus: (CH3)_x(CH2)y(CH)zCr, where the sum ofx+zis always an even number, and the sum ofx+z+ris equal to half the sum of 3x+z, whencez+ 2r=x; by this means the possible isomerides are determined. For example, for butylenes, C4H8, (CH3)2(CH)2, (CH3)2(CH2)C, (CH2)(CH2)2CH, and (CH2)4are possible.
[48 bis]Seealso method of preparing C2H2in Note12 bis.
[48 bis]Seealso method of preparing C2H2in Note12 bis.
[49]This is easily accomplished with those gas burners which are used in laboratories and mentioned in the Introduction. In these burners the gas is first mixed with air in a long tube, above which it is kindled. But if it be lighted inside the pipe it does not burn completely, but forms acetylene, on account of the cooling effect of the walls of the metallic tube; this is detected by the smell, and may be shown by passing the issuing gas (by aid of an aspirator) into an ammoniacal solution of cuprous chloride.
[49]This is easily accomplished with those gas burners which are used in laboratories and mentioned in the Introduction. In these burners the gas is first mixed with air in a long tube, above which it is kindled. But if it be lighted inside the pipe it does not burn completely, but forms acetylene, on account of the cooling effect of the walls of the metallic tube; this is detected by the smell, and may be shown by passing the issuing gas (by aid of an aspirator) into an ammoniacal solution of cuprous chloride.
[50]Amongst the homologues of acetylene CnH2n-2, the lowest is C3H4; allylene, CH3CCH, and allene, CH2CCH2, are known, but the closed structure, CH2(CH)2, is little investigated.
[50]Amongst the homologues of acetylene CnH2n-2, the lowest is C3H4; allylene, CH3CCH, and allene, CH2CCH2, are known, but the closed structure, CH2(CH)2, is little investigated.
[51]The saturated hydrocarbons predominate in American petroleum, especially in its more volatile parts; in Baku naphtha the hydrocarbons of the composition CnH2nform the main part (Lisenko, Markovnikoff, Beilstein) but doubtless (Mendeléeff) it also contains saturated ones, CnH2n+2. The structure of the naphtha hydrocarbons is only known for the lower homologues, but doubtless the distinction between the hydrocarbons of the Pennsylvanian and Baku naphthas, boiling at the same temperature (after the requisite refining by repeated fractional distillation, which can be very conveniently done by means of steam rectification—that is, by passing the steam through the dense mass), depends not only on the predominance of saturated hydrocarbons in the former, and naphthenes, CnH2n, in the latter, but also on the diversity of composition and structure of the corresponding portions of the distillation. The products of the Baku naphtha are richer in carbon (therefore in a suitably constructed lamp they ought to give a brighter light), they are of greater specific gravity, and have greater internal friction (and are therefore more suitable for lubricating machinery) than the American products collected at the same temperature.
[51]The saturated hydrocarbons predominate in American petroleum, especially in its more volatile parts; in Baku naphtha the hydrocarbons of the composition CnH2nform the main part (Lisenko, Markovnikoff, Beilstein) but doubtless (Mendeléeff) it also contains saturated ones, CnH2n+2. The structure of the naphtha hydrocarbons is only known for the lower homologues, but doubtless the distinction between the hydrocarbons of the Pennsylvanian and Baku naphthas, boiling at the same temperature (after the requisite refining by repeated fractional distillation, which can be very conveniently done by means of steam rectification—that is, by passing the steam through the dense mass), depends not only on the predominance of saturated hydrocarbons in the former, and naphthenes, CnH2n, in the latter, but also on the diversity of composition and structure of the corresponding portions of the distillation. The products of the Baku naphtha are richer in carbon (therefore in a suitably constructed lamp they ought to give a brighter light), they are of greater specific gravity, and have greater internal friction (and are therefore more suitable for lubricating machinery) than the American products collected at the same temperature.
[52]The formation of naphtha fountains (which burst forth after the higher clay strata covering the layers of sands impregnated with naphtha have been bored through) is without doubt caused by the pressure or tension of the combustible hydrocarbon gases which accompany the naphtha, and are soluble in it under pressure. Sometimes these naphtha fountains reach a height of 100 metres—for instance, the fountain of 1887 near Baku. Naphtha fountains generally act periodically and their force diminishes with the lapse of time, which might be expected, because the gases which cause the fountains find an outlet, as the naphtha issuing from the bore-hole carries away the sand which was partially choking it up.
[52]The formation of naphtha fountains (which burst forth after the higher clay strata covering the layers of sands impregnated with naphtha have been bored through) is without doubt caused by the pressure or tension of the combustible hydrocarbon gases which accompany the naphtha, and are soluble in it under pressure. Sometimes these naphtha fountains reach a height of 100 metres—for instance, the fountain of 1887 near Baku. Naphtha fountains generally act periodically and their force diminishes with the lapse of time, which might be expected, because the gases which cause the fountains find an outlet, as the naphtha issuing from the bore-hole carries away the sand which was partially choking it up.