EXERCISES

K2Cr2O7+ 2KOH = 2K2CrO4+ H2O.

When added to a solution of lead or barium salt the corresponding chromates (not dichromates) are precipitated. With barium nitrate the equation is

2Ba(NO3)2+ K2Cr2O7+ H2O = 2BaCrO4+ 2KNO3+ 2HNO3.

Potassium dichromate finds use in many industries as an oxidizing agent, especially in the preparation of organic substances, such as the dye alizarin, and in the construction of several varieties of electric batteries.

Sodium chromates.The reason why the potassium salt rather than the sodium compound is used is that sodium chromate and dichromate are so soluble that it is hard to prepare them pure. This difficulty is being overcome now, and the sodium compounds are replacing the corresponding potassium salts. This is of advantage, since a sodium salt is cheaper than a potassium salt, so far as raw materials go.

Oxidizing action of chromates and dichromates.When a dilute solution of a chromate or dichromate is acidified with an acid, such as sulphuric acid, no reaction apparently takes place. However, if there is present a third substance capable of oxidation, the chromium compound gives up aportion of its oxygen to this substance. Since the chromate changes into a dichromate in the presence of an acid, it will be sufficient to study the action of the dichromates alone. The reaction takes place in two steps. Thus, when a solution of ferrous sulphate is added to a solution of potassium dichromate acidified with sulphuric acid, the reaction is expressed by the following equations:

(1) K2Cr2O7+ 4H2SO4= K2SO4+ Cr2(SO4)3+ 4H2O + 3O,(2) 6FeSO4+ 3H2SO4+ 3O = 3Fe2(SO4)3+ 3H2O.

(1) K2Cr2O7+ 4H2SO4= K2SO4+ Cr2(SO4)3+ 4H2O + 3O,

(2) 6FeSO4+ 3H2SO4+ 3O = 3Fe2(SO4)3+ 3H2O.

The dichromate decomposes in very much the same way as a permanganate does, the potassium and chromium being both changed into salts in which they play the part of metals, while part of the oxygen of the dichromate is liberated.

By combining equations (1) and (2), the following is obtained:

K2Cr2O7+ 7H2SO4+ 6FeSO4= K2SO4+ Cr2(SO4)3+ 3Fe2(SO4)3+ 7H20.

This reaction is often employed in the estimation of iron in iron ores.

Potassium chrome alum.It will be noticed that the oxidizing action of potassium dichromate leaves potassium sulphate and chromium sulphate as the products of the reaction. On evaporating the solution these substances crystallize out as potassium chrome alum, which substance is produced as a by-product in the industries using potassium dichromate for oxidizing purposes.

Chromic anhydride(CrO3). When concentrated sulphuric acid is added to a strong solution of potassium dichromate, and the liquid allowed to stand, deep red needle-shaped crystals appear which have the formulaCrO3.This oxide of chromium is called chromic anhydride, since it combines readily with water to form chromic acid:

CrO3+ H2O = H2CrO4.

It is therefore analogous to sulphur trioxide which forms sulphuric acid in a similar way:

SO3+ H2O = H2SO4.

Chromic anhydride is a very strong oxidizing agent, giving up oxygen and forming chromic oxide:

2CrO3= Cr2O3+ 3O.

Rare elements of the family.Molybdenum, tungsten, and uranium are three rather rare elements belonging in the same family with chromium, and form many compounds which are similar in formulas to the corresponding compounds of chromium. They can play the part of metals and also form acids resembling chromic acid in formula. Thus we have molybdic acid (H2MoO4), the ammonium salt of which is (NH4)2MoO4. This salt has the property of combining with phosphoric acid to form a very complex substance which is insoluble in nitric acid. On this account molybdic acid is often used in the estimation of the phosphoric acid present in a substance. Like chromium, the metals are difficult to prepare in pure condition. Alloys with iron can be prepared by reducing the mixed oxides with carbon in an electric furnace; these alloys are used to some extent in preparing special kinds of steel.

1.How does pyrolusite effect the decolorizing of glass containing iron?

2.Write the equations for the preparation of manganous chloride, carbonate, and hydroxide.

3.Write the equations representing the reactions which take place when ferrous sulphate is oxidized to ferric sulphate by potassium permanganate in the presence of sulphuric acid.

4.In the presence of sulphuric acid, oxalic acid is oxidized by potassium permanganate according to the equation

C2H2O4+ O = 2CO2+ H2O.

Write the complete equation.

5.10 g. of iron were dissolved in sulphuric acid and oxidized to ferric sulphate by potassium permanganate. What weight of the permanganate was required?

6.What weight of ferrochromium containing 40% chromium must be added to a ton of steel to produce an alloy containing 1% of chromium?

7.Write the equation representing the action of ammonium sulphide upon chromium sulphate.

8.Potassium chromate oxidizes hydrochloric acid, forming chlorine. Write the complete equation.

9.Give the action of sulphuric acid on potassium dichromate (a) in the presence of a large amount of water; (b) in the presence of a small amount of water.

SYMBOLATOMIC WEIGHTDENSITYHIGHEST OXIDEHIGHEST CHLORIDEMELTING POINTRutheniumRu101.712.26RuO4RuCl4Electric arcRhodiumRh103.12.1RhO2RhCl2Electric arcPalladiumPd106.511.8PdO2PdCl41500°IridiumIr193.22.42IrO2IrCl41950°OsmiumOs191.22.47OsO4OsCl4Electric arcPlatinumPt194.821.50PtO2PtCl41779°GoldAu197.219.30Au2O3AuCl31064°

The family.Following iron, nickel, and cobalt in the eighth column of the periodic table are two groups of three elements each. The metals of the first of these groups—ruthenium, rhodium, and palladium—have atomic weights near 100 and densities near 12. The metals of the other group—iridium, osmium, and platinum—have atomic weights near 200 and densities near 21. These six rare elements have very similar physical properties and resemble each other chemically not only in the type of compounds which they form but also in the great variety of them. They occur closely associated in nature, usually as alloys of platinum in the form of irregular metallic grains in sand and gravel. Platinum is by far the most abundant of the six.

Although the periodic classification assigns gold to the silver-copper group, its physical as well as many of itschemical properties much more closely resemble those of the platinum metals, and it can he conveniently considered along with them. The four elements gold, platinum, osmium, and iridium are the heaviest substances known, being about twice as heavy as lead.

Occurrence.About 90% of the platinum of commerce comes from Russia, small amounts being produced in California, Brazil, and Australia.

Preparation.Native platinum is usually alloyed with gold and the platinum metals. To separate the platinum the alloy is dissolved in aqua regia, which converts the platinum into chloroplatinic acid (H2PtCl6). Ammonium chloride is then added, which precipitates the platinum as insoluble ammonium chloroplatinate:

H2PtCl6+ 2NH4Cl = (NH4)2PtCl6+ 2HCl.

Some iridium is also precipitated as a similar compound. On ignition the double chloride is decomposed, leaving the platinum as a spongy metallic mass, which is melted in an electric furnace and rolled or hammered into the desired shape.

Physical properties.Platinum is a grayish-white metal of high luster, and is very malleable and ductile. It melts in the oxyhydrogen blowpipe and in the electric furnace; it is harder than gold and is a good conductor of electricity. In finely divided form it has the ability to absorb or occlude gases, especially oxygen and hydrogen. These gases, when occluded, are in a very active condition resembling the nascent state, and can combine with each other at ordinarytemperatures. A jet of hydrogen or coal gas directed upon spongy platinum is at once ignited.

Platinum as a catalytic agent.Platinum is remarkable for its property of acting as a catalytic agent in a large number of chemical reactions, and mention has been made of this use of the metal in connection with the manufacture of sulphuric acid. When desired for this purpose some porous or fibrous substance, such as asbestos, is soaked in a solution of platinic chloride and then ignited. The platinum compound is decomposed and the platinum deposited in very finely divided form. Asbestos prepared in this way is called platinized asbestos. The catalytic action seems to be in part connected with the property of absorbing gases and rendering them nascent. Some other metals possess this same power, notably palladium, which is remarkable for its ability to absorb hydrogen.

Chemical properties.Platinum is a very inactive element chemically, and is not attacked by any of the common acids. Aqua regia slowly dissolves it, forming platinic chloride (PtCl4), which in turn unites with the hydrochloric acid present in the aqua regia, forming the compound chloroplatinic acid (H2PtCl6). Platinum is attacked by fused alkalis. It combines at higher temperatures with carbon and phosphorus and alloys with many metals. It is readily attacked by chlorine but not by oxidizing agents.

Applications.Platinum is very valuable as a material for the manufacture of chemical utensils which are required to stand a high temperature or the action of strong reagents. Platinum crucibles, dishes, forceps, electrodes, and similar articles are indispensable in the chemical laboratory. In the industries it is used for such purposes as the manufacture of pans for evaporating sulphuric acid, wires for sealing through incandescent light bulbs, and for making a great variety of instruments. Unfortunately the supplyof the metal is very limited, and the cost is steadily advancing, so that it is now more valuable than gold.

Compounds.Platinum forms two series of salts of which platinous chloride (PtCl2) and platinic chloride (PtCl4) are examples. Platinates are also known. While a great variety of compounds of platinum have been made, the substance is chiefly employed in the metallic state.

Platinic chloride (PtCl4).Platinic chloride is an orange-colored, soluble compound made by heating chloroplatinic acid in a current of chlorine. If hydrochloric acid is added to a solution of the substance, the two combine, forming chloroplatinic acid (H2PtCl6):

2HCl + PtCl4= H2PtCl6.

The potassium and ammonium salts of this acid are nearly insoluble in water and alcohol. The acid is therefore used as a reagent to precipitate potassium in analytical work. With potassium chloride the equation is

2KCl + H2PtCl6= K2PtCl6+ 2HCl.

Other metals of the family.The other members of the family have few applications. Iridium is used in the form of a platinum alloy, since the alloy is much harder than pure platinum and is even less fusible. This alloy is sometimes used to point gold pens. Osmium tetroxide (OsO4) is a very volatile liquid and is used under the name of osmic acid as a stain for sections in microscopy.

Occurrence.Gold has been found in many localities, the most famous being South Africa, Australia, Russia, and the United States. In this country it is found in Alaska and in nearly half of the states of the union, notablyin California, Colorado, and Nevada. It is usually found in the native condition, frequently alloyed with silver; in combination it is sometimes found as telluride (AuTe2), and in a few other compounds.

Mining.Native gold occurs in the form of small grains or larger nuggets in the sands of old rivers, or imbedded in quartz veins in rocks. In the first case it is obtained in crude form by placer mining. The sand containing the gold is shaken or stirred in troughs of running waters called sluices. This sweeps away the sand but allows the heavier gold to sink to the bottom of the sluice. Sometimes the sand containing the gold is washed away from its natural location into the sluices by powerful streams of water delivered under pressure from pipes. This is called hydraulic mining. In vein mining the gold-bearing quartz is mined from the veins, stamped into fine powder in stamping mills, and the gold extracted by one of the processes to be described.

Extraction.1.Amalgamation process.In the amalgamation process the powder containing the gold is washed over a series of copper plates whose surfaces have been amalgamated with mercury. The gold sticks to the mercury or alloys with it, and after a time the gold and mercury are scraped off and the mixture is distilled. The mercury distills off and the gold is left in the retort ready for refining.

2.Chlorination process.When gold occurs along with metallic sulphides it is often extracted by chlorination. The ore is first roasted, and is then moistened and treated with chlorine. This dissolves the gold but not the metallic oxides:

Au + 3Cl = AuCl3.

The gold chloride, being soluble, is extracted from the mixture with water, and the gold is precipitated from the solution, usually by adding ferrous sulphate:

AuCl3+ 3FeSO4= Au + FeCl3+ Fe2(SO4)3.

3.Cyanide process.This process depends upon the fact that gold is soluble in a solution of potassium cyanide in the presence of the oxygen of the air. The powder from the stamping mills is treated with a very dilute potassium cyanide solution which extracts the gold:

2Au + 4KCN + H2O + O = 2KOH + 2KAu(CN)2.

From this solution the gold can be obtained by electrolysis or by precipitation with metallic zinc:

2KAu(CN)2+ Zn = K2Zn(CN)4+ 2Au.

Refining of gold.Gold is refined by three general methods:

1.Electrolysis.When gold is dissolved in a solution of potassium cyanide, and the solution electrolyzed, the gold is deposited in very pure condition on the cathode.

2.Cupellation.When the gold is alloyed with easily oxidizable metals, such as copper or lead, it may be refined by cupellation. The alloy is fused with an oxidizing flame on a shallow hearth made of bone ash, which substance has the property of absorbing metallic oxides but not the gold. Any silver which may be present remains alloyed with the gold.

3.Parting with sulphuric acid.Gold may be separated from silver, as well as from many other metals, by heating the alloy with concentrated sulphuric acid. This dissolves the silver, while the gold is not attacked.

Physical properties.Gold is a very heavy bright yellow metal, exceedingly malleable and ductile, and a good conductor of electricity. It is quite soft and is usually alloyed with copper or silver to give it the hardness required for most practical uses. The degree of fineness is expressed in terms of carats, pure gold being twenty-four carats; the gold used for jewelry is usually eighteen carats, eighteen parts being gold and six parts copper or silver. Gold coinage is 90% gold and 10% copper.

Chemical properties.Gold is not attacked by any one of the common acids; aqua regia easily dissolves it, forming gold chloride (AuCl3), which in turn combines with hydrochloric acid to form chlorauric acid (HAuCl4). Fused alkalis also attack it. Most oxidizing agents are without action upon it, and in general it is not an active element.

Compounds.The compounds of gold, though numerous and varied in character, are of comparatively little importance and need not be described in detail. The element forms two series of salts in which it acts as a metal: in the aurous series the gold is univalent, the chloride having the formula AuCl; in the auric series it is trivalent, auric chloride having the formula AuCl3. Gold also acts as an acid-forming element, forming such compounds as potassium aurate (KAuO2). Its compounds are very easily decomposed, however, metallic gold separating from them.

1.From the method of preparation of platinum, what metal is likely to be alloyed with it?

2.The "platinum chloride" of the laboratory is made by dissolving platinum in aqua regia. What is the compound?

3.How would you expect potassium aurate and platinate to be formed? What precautions would this suggest in the use of platinum vessels?

4.Why must gold ores be roasted in the chlorination process?

Division of chemistry into organic and inorganic.Chemistry is usually divided into two great divisions,—organic and inorganic. The original significance of these terms was entirely different from the meaning which they have at the present time.

1.Original significance.The division into organic and inorganic was originally made because it was believed that those substances which constitute the essential parts of living organisms were built up under the influence of the life force of the organism. Such substances, therefore, should be regarded as different from those compounds prepared in the laboratory or formed from the inorganic or mineral constituents of the earth. In accordance with this view organic chemistry included those substances formed by living organisms. Inorganic chemistry, on the other hand, included all substances formed from the mineral portions of the earth.

In 1828 the German chemist Wöhler prepared urea, a typical organic compound, from inorganic materials. The synthesis of other so-called organic compounds followed, and at present it is known that the same chemical laws apply to all substances whether formed in the living organism or prepared in the laboratory from inorganic constituents. The terms "organic" and "inorganic" have therefore lost their original significance.

2.Present significance.The great majority of the compounds found in living organisms contain carbon, and the term "organic chemistry," as used at present, includes not only these compounds but all compounds of carbon.Organic chemistryhas become, therefore,the chemistry of the compounds of carbon, all other substances being treated under the head of inorganic chemistry. This separation of the compounds of carbon into a group by themselves is made almost necessary by their great number, over one hundred thousand having been recorded. For convenience some of the simpler carbon compounds, such as the oxides and the carbonates, are usually discussed in inorganic chemistry.

The grouping of compounds in classes.The study of organic chemistry is much simplified by the fact that the large number of bodies included in this field may be grouped in classes of similar compounds. It thus becomes possible to study the properties of each class as a whole, in much the same way as we study a group of elements. The most important of these classes are thehydrocarbons, thealcohols, thealdehydes, theacids, theethereal salts, theethers, theketones, theorganic bases, and thecarbohydrates. A few members of each of these classes will now be discussed briefly.

Carbon and hydrogen combine to form a large number of compounds. These compounds are known collectively as thehydrocarbons. They may be divided into a number of groups or series, each being named from its first member. Some of the groups are as follows:

METHANE SERIESCH4methaneC2H6ethaneC3H8propaneC4H10butaneC5H12pentaneC6H14hexaneC7H16heptaneC8H18octaneETHYLENE SERIESC2H4ethyleneC3H6propyleneC4H8butyleneBENZENE SERIESC6H6benzeneC7H8tolueneC8H10xyleneACETYLENE SERIESC2H2acetyleneC3H4allylene

Only the lower members (that is, those which contain a small number of carbon atoms) of the above groups are given. The methane series is the most extensive, all of the compounds up to C24H50being known.

It will be noticed that the successive members of each of the above series differ by the group of atoms (CH2). Such a series is called anhomologous series. In general, it may be stated that the members of an homologous series show a regular gradation in most physical properties and are similar in chemical properties. Thus in the methane group the first four members are gases at ordinary temperatures; those containing from five to sixteen carbon atoms are liquids, the boiling points of which increase with the number of carbon atoms present. Those containing more than sixteen carbon atoms are solids.

Sources of the hydrocarbons.There are two chief sources of the hydrocarbons, namely, (1) crude petroleum and (2) coal tar.

1.Crude petroleum.This is a liquid pumped from wells driven into the earth in certain localities. Pennsylvania, Ohio, Kansas, California, and Texas are the chiefoil-producing regions in the United States. The crude petroleum consists largely of liquid hydrocarbons in which are dissolved both gaseous and solid hydrocarbons. Before being used it must be refined. In this process the petroleum is run into large iron stills and subjected to fractional distillation. The various hydrocarbons distill over in the general order of their boiling points. The distillates which collect between certain limits of temperature are kept separate and serve for different uses; they are further purified, generally by washing with sulphuric acid, then with an alkali, and finally with water. Among the products obtained from crude petroleum in this way are the naphthas, including benzine and gasoline, kerosene or coal oil, lubricating oils, vaseline, and paraffin. None of these products are definite chemical compounds, but each consists of a mixture of hydrocarbons, the boiling points of which lie within certain limits.

2.Coal tar.This product is obtained in the manufacture of coal gas, as already explained. It is a complex mixture and is refined by the same general method used in refining crude petroleum. The principal hydrocarbons obtained from the coal tar are benzene, toluene, naphthalene, and anthracene. In addition to the hydrocarbons, coal tar contains many other compounds, such as carbolic acid and aniline.

Properties of the hydrocarbons.The lower members of the first two series of hydrocarbons mentioned are all gases; the succeeding members are liquids. In some series, as the methane series, the higher members are solids. The preparation and properties of methane and acetylene have been discussed in a previous chapter. Ethylene is present in small quantities in coal gas and may beobtained in the laboratory by treating alcohol (C2H6O) with sulphuric acid:

C2H6O = C2H4+ H2O.

Benzene, the first member of the benzene series, is a liquid boiling at 80°.

The hydrocarbons serve as the materials from which a large number of compounds can be prepared; indeed, it has been proposed to call organic chemistrythe chemistry of the hydrocarbon derivatives.

Substitution products of the hydrocarbons.As a rule, at least a part of the hydrogen in any hydrocarbon can be displaced by an equivalent amount of certain elements or groups of elements. Thus the compounds CH3Cl, CH2Cl2, CHCl3, CCl4can be obtained from methane by treatment with chlorine. Such compounds are calledsubstitution products.

Chloroform(CHCl3). This can be made by treating methane with chlorine, as just indicated, although a much easier method consists in treating alcohol or acetone (which see) with bleaching powder. Chloroform is a heavy liquid having a pleasant odor and a sweetish taste. It is largely used as a solvent and as an anæsthetic in surgery.

Iodoform(CHI3). This is a yellow crystalline solid obtained by treating alcohol with iodine and an alkali. It has a characteristic odor and is used as an antiseptic.

When such a compound as CH3Cl is treated with silver hydroxide the reaction expressed by the following equation takes place:

CH3Cl + AgOH = CH3OH + AgCl.

Similarly C2H5Cl will give C2H5OH and AgCl. The compounds CH3OH and C2H5OH so obtained belong to the class of substances known asalcohols. From their formulas it will be seen that they may be regarded as derived from hydrocarbons by substituting the hydroxyl group (OH) for hydrogen. Thus the alcohol CH3OH may be regarded as derived from methane (CH4) by substituting the group OH for one atom of hydrogen. A great many alcohols are known, and, like the hydrocarbons, they may be grouped into series. The relation between the first three members of the methane series and the corresponding alcohols is shown in the following table:

CH4(methane)CH3OH(methyl alcohol).C2H6(ethane)C2H5OH(ethyl alcohol).C3H8(propane)C3H7OH(propyl alcohol).

Methyl alcohol(wood alcohol) (CH3OH). When wood is placed in an air-tight retort and heated, a number of compounds are evolved, the most important of which are the three liquids, methyl alcohol, acetic acid, and acetone. Methyl alcohol is obtained entirely from this source, and on this account is commonly calledwood alcohol. It is a colorless liquid which has a density of 0.79 and boils at 67°. It burns with an almost colorless flame and is sometimes used for heating purposes, in place of the more expensive ethyl alcohol. It is a good solvent for organic substances and is used especially as a solvent in the manufacture of varnishes. It is very poisonous.

Ethyl alcohol(common alcohol) (C2H5OH). 1.Preparation.This compound may be prepared from glucose (C6H12O6), a sugar easily obtained from starch. If some baker's yeast is added to a solution of glucose and the temperature is maintained at about 30°, bubbles of gas aresoon evolved, showing that a change is taking place. The yeast contains a large number of minute organized bodies, which are really forms of plant life. The plant grows in the glucose solution, and in so doing secretes a substance known aszymase, which breaks down the glucose in accordance with the following equation:

C6H12O6= 2C2H5OH + 2CO2.

Laboratory preparation of alcohol.The formation of alcohol and carbon dioxide from glucose may be shown as follows: About 100 g. of glucose are dissolved in a liter of water in flaskA(Fig. 90). This flask is connected with the bottleB, which is partially filled with limewater. The tubeCcontains solid sodium hydroxide. A little baker's yeast is now added to the solution in flaskA, and the apparatus is connected, as shown in the figure. If the temperature is maintained at about 30°, the reaction soon begins. The bubbles of gas escape through the limewater inB. A precipitate of calcium carbonate soon forms in the limewater, showing the presence of carbon dioxide. The sodium hydroxide in tubeCprevents the carbon dioxide in the air from acting on the limewater. The alcohol remains in the flaskAand may be separated by fractional distillation.

Fig. 90Fig. 90

2.Properties.Ethyl alcohol is a colorless liquid with a pleasant odor. It has a density of 0.78 and boils at 78°. It resembles methyl alcohol in its general properties. It is sometimes used as a source of heat, since its flame is very hot and does not deposit carbon, as the flame from oil does. When taken into the system in small quantitiesit causes intoxication; in larger quantities it acts as a poison. The intoxicating properties of such liquors as beer, wine, and whisky are due to the alcohol present. Beer contains from 2 to 5% of alcohol, wine from 5 to 20%, and whisky about 50%. The ordinary alcohol of the druggist contains 94% of alcohol and 6% of water. When this is boiled with lime and then distilled nearly all the water is removed, the distillate being calledabsolute alcohol.

Commercial preparation of alcohol.Alcohol is prepared commercially from starch obtained from corn or potatoes. The starch is first converted into a sugar known as maltose, by the action ofmalt, a substance prepared by moistening barley with water, allowing it to germinate, and then drying it. There is present in the malt a substance known as diastase, which has the property of changing starch into maltose. This sugar, like glucose, breaks down into alcohol and carbon dioxide in the presence of yeast. The resulting alcohol is separated by fractional distillation.Denatured alcohol.The 94% alcohol is prepared at present at a cost of about 35 cents per gallon, which is about half the cost of the preparation of methyl alcohol. The government, however, imposes a tax on all ethyl alcohol which amounts to $2.08 per gallon on the 94% product. This increases its cost to such an extent that it is not economical to use it for many purposes for which it is adapted, such as a solvent in the preparation of paints and varnishes and as a material for the preparation of many important organic compounds. By an act of Congress in 1906, the tax was removed fromdenaturedalcohol, that is alcohol mixed with some substance which renders it unfit for the purposes of a beverage but will not impair its use for manufacturing purposes. Some of the European countries have similar laws. The substances ordinarily used to denature alcohol are wood alcohol and pyridine, the latter compound having a very offensive odor.Fermentation.The reaction which takes place in the preparation of ethyl alcohol belongs to the class of changes known under the general name of fermentation. Thus we say that the yeast causes the glucose to ferment, and the process is known as alcoholic fermentation. There are many kinds of fermentations, and each is thought to be due to the presence of a definite substance knownas anenzyme, which acts by catalysis. In many cases, as in alcoholic fermentation, the change is brought about by the action of minute forms of life. These probably secrete the enzymes which cause the fermentation to take place. Thus the yeast plant is supposed to bring about alcoholic fermentation by secreting the enzyme known as zymase.

Denatured alcohol.The 94% alcohol is prepared at present at a cost of about 35 cents per gallon, which is about half the cost of the preparation of methyl alcohol. The government, however, imposes a tax on all ethyl alcohol which amounts to $2.08 per gallon on the 94% product. This increases its cost to such an extent that it is not economical to use it for many purposes for which it is adapted, such as a solvent in the preparation of paints and varnishes and as a material for the preparation of many important organic compounds. By an act of Congress in 1906, the tax was removed fromdenaturedalcohol, that is alcohol mixed with some substance which renders it unfit for the purposes of a beverage but will not impair its use for manufacturing purposes. Some of the European countries have similar laws. The substances ordinarily used to denature alcohol are wood alcohol and pyridine, the latter compound having a very offensive odor.

Fermentation.The reaction which takes place in the preparation of ethyl alcohol belongs to the class of changes known under the general name of fermentation. Thus we say that the yeast causes the glucose to ferment, and the process is known as alcoholic fermentation. There are many kinds of fermentations, and each is thought to be due to the presence of a definite substance knownas anenzyme, which acts by catalysis. In many cases, as in alcoholic fermentation, the change is brought about by the action of minute forms of life. These probably secrete the enzymes which cause the fermentation to take place. Thus the yeast plant is supposed to bring about alcoholic fermentation by secreting the enzyme known as zymase.

Glycerin(C3H5(OH)3). This compound may be regarded as derived from propane (C3H8) by displacing three atoms of hydrogen by three hydroxyl groups, and must therefore be regarded as an alcohol. It is formed in the manufacture of soaps, as will be explained later. It is an oily, colorless liquid having a sweetish taste. It is used in medicine and in the manufacture of the explosives nitroglycerin and dynamite.

When alcohols are treated with certain oxidizing agents two hydrogen atoms are removed from each molecule of the alcohol. The resulting compounds are known as aldehydes. The relation of the aldehydes derived from methyl and ethyl alcohol to the alcohols themselves may be shown as follows:

Alcohols{CH3OHCorresponding aldehydes{CH2O{C2H5OH{C2H4O

The first of these (CH2O) is a gas known as formaldehyde. Its aqueous solution is largely used as an antiseptic and disinfectant under the name offormalin. Acetaldehyde (C2H4O) is a liquid boiling at 21°.

Like the other classes of organic compounds, the organic acids may be arranged in homologous series. One of the most important of these series is thefatty-acid series, thename having been given to it because the derivatives of certain of its members are constituents of the fats. Some of the most important members of the series are given in the following table. They are all monobasic, and this fact is expressed in the formulas by separating the replaceable hydrogen atom from the rest of the molecule:

H·CHO2formic acid, a liquid boiling at 100°.H·C2H3Oacetic acid, a liquid boiling at 118°.H·C3H5O2propionic acid, a liquid boiling at 140°.H·C4H7O2butyric acid, a liquid boiling at 163°.H·C16H31O2palmitic acid, a solid melting at 62°.H·C18H35O2stearic acid, a solid melting at 69°.

Formic acid(H·CHO2). The name "formic" is derived from the Latinformica, signifying ant. This name was given to the acid because it was formerly obtained from a certain kind of ants. It is a colorless liquid and occurs in many plants such as the stinging nettles. The inflammation caused by the sting of the bee is due to formic acid.

Acetic acid(H·C2H3O2). Acetic acid is the acid present in vinegar, the sour taste being due to it. It can be prepared by either of the following methods.

1.Acetic fermentation.This consists in the change of alcohol into acetic acid through the agency of a minute organism commonly called mother of vinegar. The change is represented by the following equation:

C2H5OH + 2O = HC2H3O2+ H2O.

The various kinds of vinegars are all made by this process. In the manufacture of cider vinegar the sugar present in the cider first undergoes alcoholic fermentation; the resulting alcohol then undergoes acetic fermentation. The amount of acetic acid present in vinegars varies from 3 to 6%.

2.From the distillation of wood.The liquid obtained by heating wood in the absence of air contains a large amount of acetic acid, and this can be separated readily in a pure state. This is the most economical method for the preparation of the concentrated acid.

Acetic acid is a colorless liquid and has a strong pungent odor. Many of its salts are well-known compounds. Lead acetate (Pb(C2H3O2)2) is the ordinarysugar of lead. Sodium acetate (NaC2H3O2) is a white solid largely used in making chemical analyses. Copper acetate (Cu(C2H3O2)2) is a blue solid. When copper is acted upon by acetic acid in the presence of air a green basic acetate of copper is formed. This is commonly known as verdigris. All acetates are soluble in water.

Butyric acid(H·C4H7O2). Derivatives of butyric acid are present in butter and impart to it its characteristic flavor.

Palmitic and stearic acids.Ordinary fats consist principally of derivatives of palmitic and stearic acids. When the fats are heated with sodium hydroxide the sodium salts of these acids are formed. If hydrochloric acid is added to a solution of the sodium salts, the free palmitic and stearic acids are precipitated. They are white solids, insoluble in water. Stearic acid is often used in making candles.

Acids belonging to other series.In addition to members of the fatty-acid series, mention may be made of the following well-known acids.

Oxalic acid(H2C2O4). This is a white solid which occurs in nature in many plants, such as the sorrels. Its ammonium salt ((NH4)2C2O4) is used as a reagent for the detection of calcium. When added to a solution of a calciumcompound the white, insoluble calcium oxalate (CaC2O4) precipitates.

Tartaric acid(H2·C4H4O6). This compound occurs either in a free state or in the form of its salts in many fruits. The potassium acid salt (KHC4H4O6) occurs in the juice of grapes. When the juice ferments in the manufacture of wine, this salt, being insoluble in alcohol, separates out on the sides of the cask and in this form is known as argol. This is more or less colored by the coloring matter of the grape. When purified it forms a white solid and is sold under the name of cream of tartar. The following are also well-known salts of tartaric acid: potassium sodium tartrate (Rochelle salt) (KNaC4H4O6), potassium antimonyl tartrate (tartar emetic) (KSbOC4H4O6).

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