Fig. 5.Fig. 5.
Fig. 5.
Fig. 6.Fig. 6.
Fig. 6.
2nd. The combustibility of the constituents differs: the arsenic being less combustible than the hydrogen, begins to burn only after the complete consumption of the latter body has taken place. For this reason the flame (Fig. 5) is composed of a dark portionOand a luminous portionI, which surrounds the first. The maximum temperature exists inOat the point of union of the two parts of the flame. Owing to an insufficient supply of oxygen, the complete combustion of the arsenic in this part of the flame is impossible, and if it be intersected by the cold surfaceA B, that body is deposited as a brown spot, possessing a metallic lustre. The metallic deposit originates, therefore, from the decomposition of the arsenetted hydrogen by heat and from its incomplete combustion. If the spot is not large, it fails to exhibit a metallic lustre; an experienced chemist, however, will be able to identify it by the aid of proper tests. Spots are sometimes obtained when the substanceunder examination does not contain the least trace of arsenic. These may be caused by antimony or by a portion of the zinc salt in the generating flask being carried over by the gaseous current. This difficulty is remedied by giving the apparatus the form represented in Fig. 6.Ais the flask in which the gas is generated. The delivery-tubeIconnects with a second tubeH, filled with asbestus or cotton; this is united by means of a cork with a third tubeC, made of Bohemian glass. The latter tube is quite long, and terminates in a jet at its free end, enclosed intin-foil;[C]it passes through the sheet-iron furnaceR, supported uponG. The screenDprotects the portionD Eof the tubeCfrom the heat. The gas disengaged is ignited atEand the porcelain dishPis held by the hand in contact with the flame. The apparatus being mounted, zinc, water and some sulphuric acid are placed in thegeneratingflask,[D]and the solution containing arsenious acid added: the evolution of gas commences immediately. The tubeHserves to retain any liquids that may be held suspended. The gas then passes through the partC Dof the tubeC, which is heated by placing a few live coals upon the furnaceR. The greater portion of the arsenetted hydrogen is decomposed here, and is deposited on the cold part of the tube, in a mirror-like ring. The small quantity of gas that escapes decomposition, if ignited atE, produces a metallic spot on the dishP. In order to determine that the spots are due to the presence of arsenic, and not produced by antimony, the following tests should be applied:
1. The color of the spots is distinctive: arsenical spots are brown and exhibit a metallic lustre, whereas those originating from antimony possess a black color, especially near their border. This difference is, however, not perceptible when the deposits have a large surface.
2. If the mirror be arsenical, it is readily volatilized from one part of the tube to another, when the latter is heated, and a current of hydrogen, or carbonic acid gas made to pass through it. Spots that are due to the presence of antimony are much less volatile.
3. If the tube is held in an inclined position so that a current of air traverses it, and the part containing the arsenical mirror heated, the arsenic oxidizes and arsenious acid is sublimed and deposited higher up in the tube in the form of a ring, which exhibits octahedral crystals when examined with a magnifying glass. This ring should be further tested as follows:
a.If it is dissolved in a drop of hydrochloric acid and a solution of sulphuretted hydrogen added, a yellow precipitate of sulphide of arsenic is formed. This compound is soluble in ammonia and in alkaline sulphides, but insoluble in hydrochloric acid.
b.If the ring is dissolved in pure water and an ammoniacal solution of sulphate of copper added, a beautiful green precipitate ("Scheele's green"), consisting of arsenite of copper, is produced.
4. When produced by arsenic the spots are soluble in nitric acid, and upon evaporating the solution so obtained to dryness, a residue of arsenic acid, which is easily soluble in water, remains. If an ammoniacal solution of nitrate of silver is added to the aqueous solution of the residue, a brick-red precipitate is produced. Spots consisting of antimony give, when treated with nitric acid, a residue of an intermediate oxide, insoluble in water.
5. Upon treating the spots with a drop of solution of sulphide of ammonium, the sulphide of the metal present is formed: if sulphide of arsenic is produced its properties, as enumerated above, can be recognized. It may be added that the sulphide of antimony formed is soluble in hydrochloric acid, and possesses an orange red color, whereas sulphide of arsenic is yellow.
6. When spots originating from arsenic are treated with a solution of hypochlorite of soda (prepared by passing chlorine into solution of carbonate of soda), they are immediately dissolved; if, on the other hand, they are produced by antimony, they remain unaltered by this treatment.
Such are the properties exhibited by soluble compounds of arsenic when treated by Marsh's process; the following precautions are, however, necessary when this test is made use of in medico-legal examinations.
1. If small white gritty particles, resembling arsenious acid, are discovered in the stomach or intestines, they are directly introduced into Marsh's apparatus. When this is not the case, the destruction of the organic matter is indispensable even though, instead of the organs themselves, the contents of the alimentary canal are taken. In the latter instance, the solids are separated from the fluids present by filtration, the solution evaporated to dryness and the residue united with the solid portion; the organic matter is then destroyed by one of the methods previously described. In the special case of arsenic, the separation of the poison from the accompanying organic materials can be accomplished by a process not yet mentioned which may prove to be of service. The suspected substances are distilled with common salt and concentrated sulphuric acid. By this operation the arsenic is converted into a volatile chloride which distils over. The poison is isolated by treating this compound with water, by which it is decomposed into hydrochloric and arsenious acids. We must give preference, however, to the method by means of chlorate of potassa and hydrochloric acid.
2. The solution having been obtained in a condition suitable for examination, the air is completely expelled from the apparatus by allowing the gas to evolve for some time, and the suspected fluid then introduced into the generating flask. Danger of explosion would be incurred were the gas ignited when mixed withair.[E]
3. It is indispensable, in applying this test, to have a second apparatus in which only the reagents necessary to generate hydrogen are placed: in this way, if no spots are now produced by the use of the second apparatus, it is certain that those obtained when the first apparatus is employed do not originate from impurities present in the reagents used.
It has come under the author's observation, however, that a sheet of zinc sometimes contains arsenic in one part and not in another; in fact, the shavings of this metal, as purchased for laboratory use, are often taken from lots previously collected, and may therefore have been prepared from several different sheets. If this be the case, it is supposable that the zinc used in the second apparatus may be free from arsenic, whereas the metal with which the suspected solution is brought in contact may contain this poison; serious danger would then exist of finding indications of the presence of arsenic in materials that did not originally contain a trace of the metal. In order to obviate this important objection, which might possibly place a human life in jeopardy, we propose the following modifications: Pure mercury is distilled and its absolute purity established. As the metal is a fluid and is therefore homogeneous, it is evident if one portion be found pure, the entire mass is so. Sodium is then fused under oil of naphtha, in order to cause the complete admixture of its particles, and the purity of the fused metal in regard to arsenic tested. An amalgam is next prepared by uniting the mercury and sodium. This is eminently adapted to toxicological investigations: in order to generate a supply of very pure hydrogen, it is only necessary to place the amalgam in water kept slightly acid by the addition of a few dropsof sulphuric acid, by means of which the disengagement of gas is rendered moreenergetic.[F]
It should be borne in mind that the solution introduced into Marsh's apparatus must not contain organic substances, and that, in case their destruction has been accomplished by means of nitric acid all traces of this compound are to be removed. The sulphuric acid used should also be completely freed from nitrous vapors. According toM. Blondeau, nascent hydrogen in the presence of nitrous compounds converts the acids of arsenic not into arsenetted hydrogen (As H3), but into thesolidarsenide of hydrogen (As4H2). This latter compound, upon which pure nascent hydrogen has no effect, is transformed into gaseous arsenetted hydrogen by the simultaneous action of nascent hydrogen and organic substances. These facts are of the greatest importance, for they might possibly cause a loss of arsenic when it is present, as well as determine its discovery when it is absent.
The first case is supposable: should traces of nitric acid remain in the solution, the arsenic would be transformed into solid arsenide of hydrogen and its detection rendered impossible. The second case may also occur: if the zinc placed in the apparatus contains arsenic, and the sulphuric acid used contains nitrous compounds, the evolved gas will fail to exhibit any evidence of the presence of arsenic, owing to the formation of the solid arsenide of hydrogen. Upon adding the suspected solution, which, perchance, may still contain organic substances, this arsenide is converted into arsenetted hydrogen, and the presence of arsenic will be detected, although the solution under examination was originally free from this metal.
M. Raspail suggests the following method for detecting arsenic: The surface of a brass plate is rasped by filing. In this condition the plate may be regarded as an innumerable quantity of voltaic elements, formed by the juxtaposition of the molecules of zinc and copper. The suspected materials are boiled with caustic potassa, the solution filtered, a drop of the filtrate placed upon the brass plate, and a drop of chlorine water added. If the plate is then allowed to stand for a moment and the substance under examination contains arsenic, a mirror-like spot is soon deposited upon its surface. In order to avoid confounding this deposit with those produced by other metals, the substitution of granulated brass for the plate is in some cases advisable. The granulated metal is dipped successively in the suspected solution and in chlorine water. The granules retain a small quantity of the solutions and, owing to the action of the chlorine water, become covered with metallic spots, if arsenic be present. They are then dried, placed in a tube closed at one end, and exposed to the heat of an alcohol lamp. In case the spots are arsenical, the metal volatilizes and condenses in a ring upon the cold part of the tube, which is submitted to the tests previously described.
This method can hardly be of great service, inasmuch asit extracts the poison from but a very small portion of the solution containing it: we have not, however, personally tested itsmerits.[G]
Strictly speaking the salts of antimony are more therapeutic than poisonous in their action. In fact they usually act as emetics and, under certain circumstances, may be taken in large doses without incurring serious results. There are instances, however, in which their action is truly toxical, and it becomes necessary to effect their detection in the organsof a body. It should be remarked that these salts, if absorbed, remain by a kind of predilection in the liver and spleen. A special examination of these organs should therefore be instituted, particularly if the fluids of the alimentary canal are not at hand, which is frequently the case when some time has elapsed before the investigation is undertaken.
The remarks made in the preceding article concerning the distinctive properties of arsenic and antimony need not be repeated here. The search for antimony is likewise executed by aid of Marsh's apparatus. We will confine ourselves to a description of a modification to this apparatus proposed byMM. FlandinandDanger, and employed in the separation of antimony and arsenic, when a mixture of these metals is under examination. Another process, by means of which we arrive at the same result with greater certainty and by the use of a less expensive apparatus, will then be mentioned. We will, however, first indicate the preferable method of destruction of the organic substances.
Were the decomposition performed by means of sulphuric acid, sulphate of antimony, a slightly soluble salt and one not well adapted to the subsequent treatment with nascent hydrogen, would be formed. In order to obtain the metal in a soluble state, the formation of a double tartrate of antimony and soda is desirable. This may be accomplished in the following manner:
1. A cold mixture of nitrate of soda, sulphuric acid, and the suspected materials is prepared in the proportion of 25 grammes of the nitrate to 39 grammes of the acid, and 100 grammes of the substance under examination. This mixture is heated and evaporated to dryness, and the decomposition of the organic matter completed in the usual manner. The carbonaceous residue obtained is pulverized, and then boiled with a solutionof tartaric acid. By this treatment the antimonate of soda present is converted into a double tartrate of antimony and soda, which is easily soluble in water. The solution is filtered and then introduced into Marsh's apparatus.
2. Another method consists in heating the substances under examination with one half of their weight of hydrochloric acid for six hours on a sand-bath, avoiding boiling. The temperature is then increased until the liquid is in a state of ebullition, and 15 to 20 grammes of chlorate of potassa, for every 100 grammes of the suspected matter taken, added in successive portions, so that a quarter of an hour is required for the operation. The liquid is next filtered, and the resinous matter remaining on the filter well washed with distilled water; the washings being added to the principal solution. A strip of polished tin is then immersed in the liquid: in presence of a large amount of antimony the tin becomes covered with a black incrustation: if but a minute quantity of the metal is contained, only a few blackish spots are perceptible. After the tin has remained immersed for 24 hours, it is withdrawn and placed in a flask together with an amount of hydrochloric acid sufficient for its solution in the cold. If, after several hours, blackish particles are still observed floating in the liquid, they can be dissolved in a few drops ofaqua regia. The solution may then be directly introduced into Marsh's apparatus.
Fig. 7.Fig. 7.
Fig. 7.
This apparatus consists of a wide necked jarA(Fig. 7) for the generation of the gas, the mouth of which is closed with a cork having two openings. The safety tubeS, which is funnel-shaped at its upper extremity and has its lower end drawn out to a point, passes through one of these apertures;the other opening contains the small delivery tubeB, open at both ends, and terminating in a point at its upper extremity: it is also provided with lateral openings, in order to prevent the solution being carried up to the flame. The second part of the apparatus is the condenserC, 0.03 metre in diameter, and 0.25 metre in length. This terminates at its lower extremity with a cone, and connects at the side with the tubeT, slanting slightly downwards. In the interior of the condenser, the coolerEis contained, the lower end of which is nearly in contact with the sides of the openingO. The combustion tubeD, 0.01 metre in diameter, is connected by means of a cork with the tubeT; it is bent at right angles, and encloses the tubeB, in such a manner as to allow the evolved gas to burn in its interior. The dishFis placed beneath the openingO. If the gas which burns in the combustion tube containsarsenetted hydrogen, water and arsenious acid are produced. A portion of this acid is retained in the tubeD, the remainder is carried over, with the aqueous vapor, intoC, where it condenses, and finally falls into the dishF. Both portions are subsequently examined by means of reactions necessary to establish the presence of the acid. If the ignited gas contains antimonetted hydrogen, water and an intermediate oxide of antimony are formed. The latter compound is entirely retained in the tubeDseparated from the greater part of the arsenious acid, if this body be present, and can be brought into solution by means of a mixture of hydrochloric and tartaric acids. A fluid is then obtained which can be introduced into Marsh's apparatus, or otherwise examined for antimony.
Fig. 8.Fig. 8.
Fig. 8.
Although the separation of arsenic from antimony is the chief object in making use of the apparatus proposed by Flandin and Danger, it is evident that this result is not fully accomplished, since a small portion of arsenious acid remainsin the tubeD(Fig. 7), together with the intermediate oxide of antimony. The following method secures the complete separation of these metals: An amalgam of sodium and mercury is introduced into the flaskA, (Fig. 8), which is provided with two openings. The tubeB, terminating in a funnel at its upper extremity, passes through one of these orifices. The other aperture contains a cork enclosing the small tubeC, which is bent at a right angle and communicates, by means of a cork, with the larger tubeDfilled with cotton or asbestus. A set of Liebig's bulbs,E, containing a solution of nitrate of silver, is attached to the other extremity of this tube. The apparatus being mounted, the solution under examination is slightly acidulated and introduced by means of the tubeBinto the flaskA: the disengagement of gas begins immediately. If arsenic and antimony are contained in the solution, arsenetted hydrogen and antimonetted hydrogen are evolved. Both gases are decomposed in passing through the solution of nitrate of silver contained in the Liebig bulbs: the arsenetted hydrogen causes a precipitation of metallic silver, all the arsenic remaining in solution as arsenious acid; the antimonetted hydrogen is decomposed into insoluble antimonate of silver. After the operation has continued for several hours, the apparatus is taken apart, the nitrate of silver solution thrown on a filter, and the precipitate thoroughly washed. An excess of hydrochloric acid is then added to the filtrate, and the precipitate formed separated from the solution by filtration, and well washed. The wash-water is added to the solution, and the whole then examined for arsenic by means of Marsh's test.
The precipitate formed in the nitrate of silver solution, which contains antimonate of silver, is well dried, mixed with a mixture of carbonate and nitrate of soda, and calcined in aporcelain crucible for about three-quarters of an hour. The crucible is then removed from the fire, and the cooled mass treated with hydrochloric acid until a drop of the filtered fluid ceases to give a residue when evaporated upon a watch-glass to dryness. A current of sulphurous acid is now conducted through the filtered solution until the odor of this gas remains persistent. The excess of acid is then removed by boiling, and the solution placed in Marsh's apparatus and tested for antimony.
If a mercurial salt exists in a considerable quantity in the substances extracted from the alimentary canal, or ejected either by stools or vomiting, it can be isolated by treating these materials with water, filtering the liquid, and evaporating the filtrate to dryness. The residual mass is taken up with alcohol, and the solution again filtered and evaporated. Upon dissolving the residue obtained by this operation in ether and filtering and evaporating the solution, a residue is obtained which when dissolved in water forms a fluid wherein the presence of mercury can be detected by means of the ordinary tests.
When, however, only a minute quantity of mercury is present, and this has been absorbed, its detection is more difficult. It will be necessary under these circumstances to make use of either Smithson's pile or Flandin and Danger's apparatus.
Smithson's pile consists of a small plate of copper around which a piece of thin gold foil is wrapped. This is immersed in the solution to be tested for mercury, which has previouslybeen slightly acidulated: if mercury be present, the plate acquires a white color which disappears upon exposure to the flame of a spirit-lamp. A similar reaction occurs in presence of tin, as this metal would likewise be deposited upon the plate, and, upon heating, would penetrate the metal and restore to it its natural color. The danger of mistake arising from this fact is obviated by introducing the copper plate into a tube closed at one end and bent at a right angle. The open extremity of the tube is drawn out to a fine point and immersed in water contained in a second tube also closed at one end. Upon heating the plate in the flame of an alcohol lamp, the white color disappears if produced by mercury, and at the same time this metal condenses in the narrow extremity of the tube. The metallic globules formed can be recognized either by the naked eye or with the aid of a lens, or by rubbing them with a piece of gold foil when the latter will acquire a white coating.
When Smithson's pile is employed, the organic substances are most advantageously decomposed by means of chlorine. It is advisable to operate with as small a quantity of fluid as possible, for, owing to the volatility of bichloride of mercury, a portion of this salt may be lost by the evaporation of aqueous, alcoholic, and even etherial solutions, and the detection of minute quantities rendered impossible.
Fig. 9.Fig. 9.
Fig. 9.
This apparatus consists of a standS, (Fig. 9) supporting a balloonA, which serves as the reservoir of the suspected solution, and a funnelB, into which the neck of the balloon is dipped. The funnelBis bent at a right angle and is drawn out at its lower end under which the dishCis placed for the reception of the escaping fluids. A fine wire of pure gold,forming the negative electrode of a Bunsen's battery, passes through the lower extremity of the funnel. The end of this wire nearly comes in contact with a second wire, inserted in the upper part of the funnel, and connected with the positive pole of the battery. If the balloon filled with the solution is inverted and immersed in the funnelB, its neck will be submerged at first; soon, however, it becomes uncovered, owing to the depression of the level of the fluid caused by the escape of the latter through the tapering extremity of the funnel: a bubble of air then passes in the balloon and expels a drop of the solution. This process is repeated at short intervals, causing a continuous flow of the fluid, the rapidity of which is easily regulated by elevating or lowering the balloon, thus raising or depressing the level of the liquid. The apparatus having been mounted in this manner and the battery set in action, the disengagement of gas commences. Should mercury be contained in the solution under examination, this metal will be deposited upon the negative wire. When the operation is completed this wire is detached from the apparatus, washed with ether, and dried. It is then introduced into a small tube provided with a bulb, and the mercury volatilized by means of the blow pipe flame: the metal condenses in the bulb of the tube in globules which are readily recognized. They can also be dissolved in nitric acid, and the presence of a mercurial salt in the solution confirmed by further tests.
The solution to be examined in the preceding apparatus, is prepared as follows:
The suspected organic matter is treated with cold sulphuric acid of 66°B.until liquefied, and hypochlorite of lime, and distilled water then added: if necessary, the evolution of chlorine can be accelerated by a further addition of sulphuric acid. As soon as the liquid becomes clear, it is filtered, concentrated and examined as described above. The solution contains the mercury in the state of bichloride, a salt soluble in water and well adapted to the above test.
The substitution of a large balloon, having a capacity of about 2 litres, in place of the small vessel of Flandin and Danger's apparatus, is to be recommended as doing away with the necessity of evaporation; an operation which invariably causes a loss of substance. The apparatus, modified in this manner, is the most delicate in use for the detection of mercury.
The solid substances found in the alimentary canal are mechanically separated from the fluids present by means of a linen cloth. They are then examined by aid of a magnifying glass, and any fragments of phosphorus found separated and preserved under water. If none are discovered, the presence of phosphorescent vapors may possibly be detected by examining the materials in the dark. In any case, a portion of the suspected materials should be treated with nitrate of silver: in presence of phosphorus the materials acquire, first, a reddish-brown, then, a black color. The remainingportion is spread upon a shovel and heated: a white flame, burning at various points of the mass, and originating from the combustion of phosphorus, is observed, if this body be contained in the substances under examination. This method is evidently far from perfect.
Mistcherlich's method is based upon the luminosity of the vapors of phosphorus. The suspected materials are moistened with dilute sulphuric acid, and heated, in a flask communicating with a glass worm which passes through a glass cooler into a receiver. If the apparatus is placed in the dark, and the materials contain phosphorus, luminous vapors will be observed in the flask and receiver. When the quantity of the poison present is considerable, the phosphorous acid formed can be collected and its properties tested.
Fig. 10.Fig. 10.
Fig. 10.
Dusart's process takes advantage of the facility with which hydrogen combines with phosphorus. The substances under examination are placed between two asbestus stoppers in a tube, one end of which tapers to a point, and a current of pure hydrogen conducted over them. In presence of phosphorus the evolved gas will burn with a green flame, and, upon bringing this in contact with a porcelain plate, red spots will be deposited upon the latter.Blondlotprefers to introduce the suspected materials into the flask in which the hydrogen is generated. He employs the apparatus represented in Fig. 10:ais a flask for evolving hydrogen;bis a U tube, filled with fragments of pumice stone which are saturated with a concentrated solution of potassa;cis a Mohr clamp;da screw-clamp;ea platinum jet. This jet is necessary inorder to avoid a yellow coloration of the flame by the soda contained in the glass. Pure hydrogen is at first evolved, in order to ascertain that the flame is colorless and red spots are not produced when it is intersected by a cold plate. The purity of the reagents used having thus been confirmed, theclampdis closed until the acid is forced back intof; and the materials to be examined are then added to the fluid. Upon opening the clamp the liquid passes fromfintoa, and the evolution of gas recommences. The gas is then ignited: the flame possesses the characteristic properties mentioned above, if the suspected substances contain phosphorus.
According to this method, the materials are brought into a flask provided with a doubly-perforated stopper, and water, acidulated with sulphuric acid, added. The flask is then heated over a water-bath, and a current of carbonic acid conducted through the mixture for at least two hours. The gas, on leaving the flask, passes into a solution of nitrate of silver. Should no precipitate form in this solution, the absence of free phosphorus is established, for, were this body present, a portion would be volatilized, and a black precipitate, consisting of phosphide of silver, together with phosphoric acid, produced. The formation of a black precipitate is, however, not necessarily a proof of the presence of phosphorus. In order to conclusively determine the character of the precipitate, it is collected on a filter and examined by the method of Dusart and Blondlot.
This process has given result in cases where none were obtained by Mistcherlich's method. It possesses, moreover, an advantage over the latter process, in not being influenced by the presence of foreign bodies; whereas, in Mistcherlich's method, some time must elapse before the luminosity of the vapors becomes apparent if ether or alcohol is contained in the solutions, and this phenomenon totally fails to appear in presence of oil of turpentine.
In a report read before the Academy of Sciences in 1856, presented by an examining commission, of which MM.Dumas,PelouzeandClaude Bernardwere the reporters, the following results were contained: Phosphorus may remain, in thefree state, in the organs fifteen days after death, and even then its isolation can easily be accomplished. For this purpose the stomach or intestines, and the articles of food contained therein, are cut into pieces and treated with bisulphide of carbon. Upon filtering the liquid, a solution is obtained containing all the phosphorus present, which exhibits the following properties: 1st, When ignited, it burns with a very luminous flame; 2nd, if allowed to spontaneously evaporate (the combustion of the phosphorus being prevented by the organic matter present [Naquet]) an inflammable residue is obtained, which, if dissolved in boiling monohydrated nitric acid, gives a solution that, after saturation with ammonia, produces a precipitate soluble in acids in solutions of barium salts. If the solution is mixed with perchloride of iron, and the sesquioxide of this metal subsequently eliminated by the addition of ammonia, it no longer causes a precipitation in barium solutions. The fluid acquires a yellow coloration when boiled with a solution of molybdate of ammonia.
According to our personal experience, the apparatus employed by Flandin and Danger for the detection of arsenic, can also be made use of in the examination of the bisulphide of carbon solution. To this end, the fluid supposed to contain phosphorus is mixed with perfectly pure alcohol, and the mixture placed in a small spirit-lamp provided with a very loose asbestus wick. The lamp is then ignited and the flame introduced in the combustion tubeD(Fig. 11).
Fig. 11.Fig. 11.
Fig. 11.
By the combustion of the mixture, sulphurous, carbonic, phosphorous acids and water are formed. The water condenses inc, and, falling into the dishF, carries with it the sulphurous and phosphorous acids. The acid liquid collected in this way is evaporated to dryness, some nitric acid added, and the solution again evaporated. The remaining mass is then dissolved in water to which some ammonia is added, and the solution tested for phosphoric acid. This method is an advantageous one as the phosphoric acid formed must originate from phosphorus in thefree state, and not from any phosphates which, owing to the presence of organic matter, might be contained in the bisulphide of carbon solution. It would, however, lead the analyst into error if the person, supposed to have been poisoned had eaten cerebral substances or eggs previous to death, as these contain glycero-phosphoric acid; it is therefore advisable to compare the results given by this process with those obtained by the use of other methods.
Provided free phosphorus has not been detected, it is necessary to search for phosphorous acid. To this end, the residue remaining in the flask, in either Mistcherlich's or Fresenius and Neubauer's method, is introduced into the apparatus of Dusard and Blondlot. If the phosphorus reaction appears, it is sufficient; otherwise, its production may have been hindered by the presence of organic matter. In case, therefore, the flame is colorless, the evolved gas is conducted into a neutral solution of nitrate of silver. If the materials contain phosphorous acid, a precipitate of phosphide of silver is formed which should be collected and washed. The precipitate, which is now free from organic matter, is then examined for phosphorous acid by means of the apparatus of Dusard and Blondlot.
The best process for determining quantitatively the amount of phosphorus present is the one recommended by Fresenius and Neubauer. The gaseous current is continued until a fresh nitrate of silver solution is no longer precipitated. The solution is filtered, the precipitate washed and then dissolved in nitric acid. The silver is next precipitated by addition of hydrochloric acid, the fluid again filtered, and the precipitate well washed. The washings are added to the filtrate, and the liquid concentrated in a porcelain capsule. A solution of sulphate of magnesia, containing ammonia, is next added to the fluid, and the phosphoric acid determined as pyrophosphateof magnesia: the precipitate formed, is washed, heated to redness, in order to convert it into the pyrophosphate, and then weighed.
The search for acids is to be instituted exclusively in the alimentary canal and its contents. Were acids contained in the other organs, their presence would be due to the blood in which they had previously been absorbed, and, as in this case they would be partially neutralized by the bases contained in the blood, a conclusive decision in regard to their original existence in the suspected materials would be impossible, the salts of the acids usually searched for being normal constituents of the blood. In order to detect the presence of acids, the alimentary canal and contents are first boiled with water which is renewed until the solution ceases to exhibit an acid reaction when tested with litmus paper. The fluid is then filtered, alcohol added to the filtrate, in order to precipitate organic substances, the liquid again filtered, and the solution tested separately for the various acids as directed below.
The solution is placed in a retort provided with a receiver and distilled until the residual fluid assumes a pasty consistence: the operation is then discontinued. If hydrochloric acid be present in the materials under examination, the distillate will have an acid reaction, and, upon addition of solution of nitrate of silver, a white precipitate, which is easily soluble in ammonia but insoluble in nitric acid and in short possesses all the properties of chloride of silver, will be formed.
The distillate, obtained as in the preceding process, is neutralized by the addition of potassa or soda, and evaporated to dryness. The residue is mixed with copper filings, and introduced into a glass tube closed at one end and provided at the other with a cork through which a delivery-tube passes. Sulphuric acid is then added to the mixture, the cork inserted, the tube heated, and the evolved vapors conducted into a solution of protosulphate of iron. The latter solution acquires a brown coloration which, upon addition of sulphuric acid, changes to a violet, if nitric acid be present. Upon conducting the disengaged gas into a solution of narcotine, the latter acquires a beautiful red color.
Another portion of the residue should deflagrate when saturated with an alkali and projected upon live coals.
In order to detect this acid, the solution obtained by treating the organs with water is not distilled but is concentrated to one-sixth of its original volume, and then agitated with ether for about ten minutes. By this treatment the ether takes up the free sulphuric acid, but not the acid sulphates present. After ten minutes contact, the ether is decanted and allowed to spontaneously evaporate. Upon treating the residue, which contains the free sulphuric acid and fatty substances, with water, a solution containing only the sulphuric acid is obtained. Nitrate of baryta is then added to a portion of the fluid: in presence of sulphuric acid, a white precipitate, insoluble in acids, is produced. If this is heated on charcoal before the blow-pipe, a mass is formed, which, when moistenedwith hydrochloric acid and placed upon a clean silver coin, produces a black spot on the metal. Another portion of the solution is mixed with copper and the mixture evaporated in a tube closed at one end: sulphurous acid is evolved towards the end of the operation. This gas is detected by allowing it to pass over paper saturated with a mixture of iodic acid and starch; a blue coloration is produced which, owing to the transformation of the iodine set free into hydriodic acid, subsequently disappears. (We have never been able to effect the disengagement of sulphurous acid spoken of above when an exceedingly dilute sulphuric acid was used, even upon evaporating the mixture to dryness, notwithstanding Orfila's statement that the reaction occurs very readily.)
The aqueous solution is evaporated to dryness, the residue taken up with alcohol of 44° B., the fluid again evaporated, and the second residue dissolved in water. Upon adding acetate of lead to the solution, a white precipitate is produced if phosphoric acid be present. The precipitate is washed, suspended in water and a current of sulphuretted hydrogen passed through the mixture. If the fluid is then filtered, and the excess of sulphuretted hydrogen expelled from the filtrate by boiling, a liquid possessing the distinctive properties of a solution of phosphoric acid will be obtained. This should then be submitted to the following tests: Some pulverized charcoal is added to a portion of the solution, the mixture evaporated to dryness, and the residue obtained introduced into a Hessian crucible heated to redness: in presence of a considerable amount of the acid, free phosphorous is liberated and burns with a bright flame in the upper part of the crucible. Incase this reaction fails to occur, other portions of the fluid are treated with a solution of a baryta salt, which causes a white precipitate, soluble in nitric acid; with an ammoniated solution of sulphate of magnesia, which throws down a crystalline white precipitate; and by boiling with molybdate of ammonia, acidulated with nitric acid, which produces a yellow precipitation, or at least a yellow coloration of the solution.
The solution is subjected to the same treatment as in the search for phosphoric acid, with the exception that, instead of adding acetate of lead to the fluid obtained by taking up the residue left from the alcohol with water, it is divided into two portions which are examined separately. A solution of a lime salt is added to one portion: if oxalic acid be present, a precipitate, which is insoluble in acetic acid or in chloride of ammonium, and effervesces when slightly calcined and treated with hydrochloric acid, is formed. Nitrate of silver is added to the remaining portion of the solution: the formation of a precipitate, which detonates when dried and heated in a glass tube closed at one end, is further evidence of the presence of the acid.
The solution obtained by treating the alimentary canal with water is distilled, as in testing for nitric and hydrochloric acids, and the following properties verified in the distillate: 1st. It has an acid reaction, and possesses the odor of vinegar; 2nd, unless previously neutralized with a base, it fails to redden the per-salts of iron; 3rd, if the distillate is added to a solution ofthe per-salts mentioned and sulphuretted hydrogen conducted through the fluid, a black precipitate is formed; 4th, upon boiling the still acid fluid with a small quantity of starch, the property of the latter to become colored in presence of free iodine is not changed; 5th, if heated with an excess of litharge, a basic salt which restores the blue color to reddened litmus paper is produced.
The detection of hydrocyanic acid requires special precautions. The substances to be examined are mixed with water, if solids are present, and introduced into a retort provided with a delivery-tube which dips in a solution of nitrate of silver. The retort is then heated over a water-bath. If the evolved vapors produce a precipitate in the silver solution, the heating is continued until a fresh portion of the latter is no longer affected. The operation is now interrupted, hydrochloric acid added to the retort, and heat again applied. Should a second precipitation of cyanide of silver occur, the presence of acyanidein the suspected materials is indicated; whereas the formation of a precipitate by the simple action of heat would point to the presence of free hydrocyanic acid or cyanide ofammonium.[H]In case the latter compound is present, ammonia will be contained in the distillate.
In order to identify the cyanogen, a portion of the precipitate is collected upon a small filter, washed, dried, and then allowed to fall into a rather long tube, closed at one end, in the bottomof which some iodine has previously been placed. A column of carbonate of soda is then introduced above the precipitate for the purpose of retaining the excess of iodine probably taken. Upon heating the lower end of the tube, white fumes of iodide of cyanogen, which condense in needles upon the cold portion of the tube, are produced. These are easily recognized by aid of a magnifying glass. They are colorless and are readily volatilized by heat. Some ammonia is next added to a solution of protosulphate of iron, the precipitate formed thoroughly washed, and exposed to the air until it acquires a greenish hue. The iodide of cyanogen is then withdrawn from the tube and mixed with potassa-lye and the precipitate mentioned above. The mixture is evaporated to dryness, the residue obtained treated with water and the filtered solution then acidulated with hydrochloric acid. If a solution of a persalt of iron is now added to the fluid, a blue precipitate is formed. The addition of salts of copper produces a reddish precipitation.
The remainder of the precipitate formed in the nitrate of silver solution is heated with sulphur and then boiled with an aqueous solution of chloride of sodium: if cyanogen is contained in the precipitate, a solution of sulphocyanate of soda will be formed, and upon adding sesquichloride of iron an intense red coloration produced.
It is evident that the presence of another acid in the solution examined for hydrocyanic acid would render the detection ofcyanidesimpossible, but in all cases hydrocyanic acid can be separated without arriving at a decision in regard to its original state of combination. Nitric, hydrochloric, and several other acids would not be distilled at the temperature of the water-bath; an examination for these by the methods already described can therefore be instituted simultaneously with the search for hydrocyanic acid.
The separation of these bodies in the caustic state is a matter of difficulty owing to the great tendency they possess to become converted into carbonates; the carbonates of lime, baryta and strontia, moreover, being non-poisonous in their effects, will not be employed with criminal intent, and the carbonates of soda and potassa are extensively used as pharmaceutical preparations. Notwithstanding the small chances of success, the isolation of the compounds under consideration in the caustic state is to be attempted.
To this intent, the organs to be analysed, together with their contents, are placed in a glass retort provided with a receiver, water added, and the mixture boiled. The distillate will contain the ammonia present. When, however, putrefaction has begun, the detection of this compound does not necessarily indicate its original presence in the suspected materials. If, after an hour's boiling, the fluid in the retort possess an alkaline reaction, it is to be examined for soda, potassa, strontia, baryta and lime. The undistilled solution is filtered, the filtrate evaporated to dryness, and the residual mass treated with alcohol. By this treatment, potassa and soda go in solution, lime, baryta andstrontia[I]—as well as the alkaline carbonates—remaining undissolved. The potassa and soda are separated from the other salts present by filtering and evaporating the alcoholic solution to dryness and then calcining the residue in a silver crucible. The mass, which should still be alkaline, is then dissolved in dilute sulphuric acid. If the solution is turbid, traces of baryta or strontia may still be present and should beremoved by filtration. Some hydrochloric acid and solution of bichloride of platinum are then added to a portion of the filtered liquid: in presence ofpotassaa yellow precipitate is formed.
Another portion is treated with tartaric acid: a white granular precipitate is produced. Hydrofluosilicic acid is added to a third portion of the solution: the formation of a gelatinous precipitate is a further indication of the presence of potassa. If the preceding tests have given negative results, and a white precipitate is formed by the addition of antimonate of potassa to another portion of the solution,sodais present. In both cases, it is necessary to confirm the results by means of the spectroscope.
The above reactions are distinctive only in the absence of metals precipitated by sulphuretted hydrogen, sulphide of ammonium or carbonate of soda, and small portions of the solution should be tested with these reagents.
In order to detect baryta, strontia and lime, the residue, insoluble in alcohol is dissolved in dilute nitric acid, and an excess of carbonate of ammonia added to the solution: the three bases, if present, are precipitated as carbonates. The precipitate formed is separated from the solution by filtration, dissolved on the filter in dilute hydrochloric acid, and the solution then filtered and divided into two parts: sulphuric acid is added to one, the fluid filtered from the precipitate of sulphate of baryta formed, and the filtrate treated with ammonia and oxalate of ammonia. Iflimebe present,—although its sulphate is not easily soluble—sufficient will be contained in the filtrate to give a white precipitate of oxalate of lime.
The remaining portion of the solution is evaporated to dryness, and the residue treated with absolute alcohol. Chloride of strontium goes into solution, chloride of barium remaining undissolved. If upon evaporating the alcoholic solution aresidue is obtained which, when dissolved in water, produces turbidity in a solution of sulphate of lime,strontiais present.
The residue, insoluble in alcohol, is dissolved in water. If a precipitate is produced by the addition of sulphuric acid or hydrofluosilicic acid to the solution,barytais present. The latter reaction distinguishes baryta from strontia, which is not precipitated by hydrofluosilicic acid. Should the tests mentioned above fail to give affirmative results, and poisoning by means of baryta and strontia be nevertheless suspected, these compounds may possibly have remained in the materials contained in the alimentary canal, in the state of insoluble sulphates. To effect their detection under these circumstances the organic substances must be decomposed by means of sulphuric acid. The carbonaceous residue is calcined in a crucible at an elevated temperature, and the remaining mass treated with water. In this way, a solution of sulphides of barium and strontium is obtained, which is then tested as directed above.
The detection of chlorine is very difficult owing to the great tendency it possesses to become converted into chlorides or hydrochloric acid, and it is only when found in a free state that its discovery is of importance.
In case the gas exists uncombined in the alimentary canal, its odor will be perceptible, and, upon boiling the suspected materials with water, vapors will be evolved which impart a blue color to paper saturated with a mixture of iodide of potassium and starch paste. If the addition of sulphuric acid is necessary in order to produce the above reactions, there isreason to suspect the presence of "chloride of lime" or"Eau de Javelle."[J]
In case bromine exists in a free state at the time the autopsy is made, its presence will be detected by the reddish color and unpleasant odor it possesses. Its isolation is accomplished by treating the materials with bisulphide of carbon which, upon dissolving the bromine, acquires a red color. If potassa is then added to the solution, it combines with the bromine and, upon evaporating the decanted fluid, calcining the residue, and treating it with water, a solution of bromide of potassium is obtained. Upon adding chlorine-water and ether to a portion of the fluid, and shaking the mixture, the bromine is liberated and is dissolved by the ether. The etherial solution of bromine, which possesses a reddish-yellow color, does not mingle with, but floats upon the surface of the colorless aqueous solution.
If nitrate of silver is added to another portion of the aqueous solution of bromide of potassium, a precipitate of bromide of silver, soluble in ammonia, is formed.
In case the bromine has been converted into a bromide, it is necessary to boil the alimentary canal and the articles of food contained therein with water. The fluid is next filtered and agitated with chlorine-water and ether. The liberated bromine is dissolved by the ether, which acquires a reddish-yellow color. Upon decanting the solution, and treating it with potassa, bromide of potassium is formed, and can be detected as directed above.
The detection of iodine is accomplished by a process almost identical with the above. The isolation of the iodine having been effected, it remains to be ascertained that it imparts a blue color to starch paste, and a violet color to bisulphide of carbon.
Under this head we will indicate the systematic course of analysis to be pursued, supposing a mixture of several metals including arsenic and antimony, to be under examination.
The organic substances are first destroyed by means of chlorate of potassa and hydrochloric acid. When this is accomplished, the excess of chlorine is removed by boiling and the liquid filtered. The portion remaining on the filter is preserved: it contains all the silver and a large portion of the lead, if these metals are present. We will designate the residue as A, the filtrate as B.
The residue is calcined with a little carbonate of soda and cuttings of pure Swedish filtering paper, the chlorides present being reduced to the metallic state by this treatment. The residue is next taken up with water acidulated with nitric acid, and the solution filtered. An insoluble residue, that may remain, is washed with hot water until the wash-water ceases to precipitate solution of nitrate of silver, and dried. It is then dissolved in boiling nitric acid, the solution diluted with water, andfiltered.[K]
Sulphuric acid is added to the filtrate: if no precipitate forms, the absence oflead, in the residue A, is indicated. If, on the contrary, a precipitate is produced, it is collected upon a filter and washed. In order to make sure that the precipitate consists of sulphate of lead, it is treated with a solution of tartrate of ammonia: it should dissolve, forming a solution in which sulphuretted hydrogen produces a black precipitate.
The fluid which has failed to be precipitated by the addition of sulphuric acid, or the filtrate separated from the precipitate formed, can contain only silver. Upon adding hydrochloric acid, this metal is thrown down as a caseous white precipitate, which is soluble in ammonia, but insoluble in boiling nitric acid, and blackens upon protracted exposure to light. The formation of a precipitate possessing these properties, leaves no doubt as to the presence ofsilver.
Remark.—In the operations described above, as well as in those following, the difficulty in separating minute precipitates from the filter is often experienced. When the precipitate is to be dissolved in reagents that do not affect the paper, such as ammonia, tartrate of ammonia, and dilute acids, it can be brought in solution directly on the filter. In cases, however, where reagents which attack the paper are employed, the precipitate should be separated. This is accomplished by mixing a small quantity of pure silica, obtained by the decomposition of fluoride of silicium by water, with the solution, before filtering. The precipitate becomes intimately mixed withthe silica, and can then be readily removed from the paper. The presence of silica does not interfere, it being insoluble in the reagents commonly made use of.
A current of sulphuretted hydrogen is conducted for twelve hours through the solution, which is kept at a temperature of 70°. by means of a water-bath. The flask containing the liquid is then closed with a piece of paper, and allowed to remain in a moderately warm place until the odor of the gas is no longer perceptible. The solution is next filtered with the precaution mentioned in the preceding remark, and the precipitate (a) thoroughly washed. The water used in this operation is united to the filtrate, and the fluid (b) examined as directed further on.
In order to free the precipitate from the organic substances possibly present, at the same time avoiding a loss of any metal, it is dried, moistened with nitric acid, and the mass heated on a water-bath. Some Swedish filtering paper is next added, the mixture well impregnated with sulphuric acid, and then maintained for several hours at a temperature of about 170°. until a small portion (afterwards returned) gives a colorless solution when treated with water. The residue is now heated with a mixture of one part of hydrochloric acid and eight parts of water, the liquid filtered, the matter remaining undissolved washed with dilute hydrochloric acid, and the washings united with the filtrate.
The residueI.and the solutionII.are separately examined as directed below.
This may contain lead, mercury, tin, bismuth and antimony. It is heated for a considerable time withaqua regia, the solution filtered, and the second residue, should one remain, washed with dilute hydrochloric acid. If the second residue is fused with cyanide of potassium, the compounds present are reduced to the metallic state. The liberated metals are treated with nitric acid, which dissolveslead, but leavestinas insoluble metastannic acid. The nitrate of lead is then filtered from the metastannic acid, and both metals are identified as described in the treatment of residue A.
The solution, obtained by the action ofaqua regiaon residue I, is treated with sulphuretted hydrogen. The tin and antimony are separated from the lead, mercury and bismuth by treating the precipitate produced with sulphide of ammonium, which dissolves only the sulphides of the first two metals. The solution in sulphide of ammonium is afterwards examined for these metals, as directed under the head of solution IV., the search for arsenic, however, being here omitted.
Upon treating the residue insoluble in sulphide of ammonium with nitric acid, lead, copper and bismuth go into solution, mercury remaining undissolved. The liquid is filtered, and the undissolved mercury submitted to the special examination previously described.
Sulphuric acid is added to the solution and the precipitate of sulphate of lead formed, separated, washed, and examined as directed while treating of residue A.
Finally, the solution separated from the lead is tested forbismuthandcopper, as in examination of precipitate III.
The solution is concentrated by heating on a water-bath, a small quantity of carbonate of soda cautiously added to a portion, and notice taken if a precipitate forms. The part taken is then acidulated with a little hydrochloric acid, returned to the principal solution, and sulphuretted hydrogen conducted through the fluid, as in the examination of solution B. In case a precipitate fails to form, all metals are absent; if, on the contrary, a precipitate (c) is produced, it is examined as directed below.
If the solution merely became turbid, or the precipitate formed was of a pure white color, it consists probably of sulphur. It is, however, indispensable, even in this case, to collect the precipitate and examine it forarsenic. Provided it is of a pure yellow color, it is treated with ammonia. In case it is entirely dissolved by this treatment, and the addition of carbonate of ammonia failed to produce a precipitate in solution II., it is certain that arsenic, and no other metal, is present. Under these circumstances, the ammoniacal solution is examined as directed in the article on the detection of arsenic. If, on the other hand, the precipitate is not yellow, or being yellow, is but imperfectly soluble in ammonia, and a precipitate was formed by the addition of carbonate of ammonia to solution II., it is necessary to likewise search for tin, antimony, mercury, copper, bismuth and cadmium. In this case, the precipitate is placed in a small flask, allowed to digest for several hours with ammonia and sulphide of ammonium in a moderately warm place, and the solution filtered.
The remaining residue (III.) is washed, labelled, and preserved for subsequent examination; thefiltrate(IV.) is treated as directed below.
The solution, to which the water used in washing the residue has been added, is evaporated to dryness, the residue obtained taken up with pure fuming nitric acid, and the liquid again evaporated. The second residue is next saturated with a solution of carbonate of soda. A mixture of 1 part of carbonate and 2 of nitrate of soda is then added, the mixture evaporated to dryness, and the residual mass heated to fusion. The fused mass, when cold, is treated with cold water, and any remaining residue washed with a mixture of equal parts of alcohol and water. The filtered fluids are now evaporated in order to remove the alcohol, sulphuric acid is then added, and the mixture heated until white fumes of the acid begin to evolve. In this way the complete expulsion of the nitric acid present is rendered certain. When cold, the residue is treated with water and thesolutionintroduced into Marsh's apparatus, or, in case a quantitative estimation of the arsenic is desired, it is treated with sulphuretted hydrogen and the weight of the precipitate formed determined, as directed under the detection of arsenic.
Should a residue insoluble in water remain, it may contain tin, antimony and traces of copper. Upon dissolving it inaqua regiaand placing a sheet of pure zinc in the solution, these metals are thrown down in the metallic state. The precipitate is collected, the zinc present completely removed by treatment withdilutehydrochloric acid, and the residue boiled with concentrated hydrochloric acid which dissolves thetinpresent.The fluid is filtered and thefiltratetested for this metal by adding solution of chloride of gold, which, in its presence, produces a purple precipitate, and, by treating it with sulphurated hydrogen, which forms a brown precipitate, soluble in sulphide of ammonium.
If theresidue, insoluble in concentrated hydrochloric acid, is thoroughly washed and then treated with nitric acid, the copper present goes in solution. The fluid is filtered, and ammonia added to the filtrate: in presence ofcopper, the solution acquires a blue color, and gives a reddish precipitate upon addition of ferrocyanide of potassium.
Antimony, if present, remains by the treatment with nitric acid as an insoluble intermediate oxide. This is dissolved in hydrochloric acid, in which it is now soluble, and the solution introduced into Marsh's apparatus.
This precipitate may contain the sulphides of mercury, copper, cadmium and bismuth. Upon treating it with nitric acid, all but the sulphide of mercury are dissolved. In case no residue remains, the absence ofmercuryis indicated; if, on the other hand, a residue is left, it is well washed, dissolved inaqua regia, and the solution examined, either by means of Smithson's pile, or in the apparatus of Flandin and Danger. (VideDetection of Mercury.)
Whether a residue remains or not, an excess of ammonia is next added to the filtered solution in nitric acid: the formation of a permanent precipitate denotes the presence ofbismuth. In this case, the fluid is filtered, and the alkaline filtrate further tested for copper and cadmium. For this purpose, cyanide of potassium is added, and sulphuretted hydrogen conducted through the filtrate: ifcadmiumbe present, a yellow precipitate is produced, copper not being thrown down in presence of an alkaline cyanide. The precipitate of sulphide of cadmium is separated from the solution by filtration, and the filtrate saturated with hydrochloric acid.Copper, if present, is now precipitated as sulphide: its separation is completed by conducting sulphuretted hydrogen through the fluid.
The precipitate is collected, washed, dissolved in nitric acid, and its identity established as previously directed. If the metal be present in sufficient quantity, it should be obtained in a metallic state upon a plate of iron; it is then coherent, possesses its natural color, and can conveniently be exhibited to the Jury.
This solution may contain: cobalt, nickel, iron, manganese, chromium, zinc and aluminium. Of these, only zinc and chromium are poisonous; the search for these two metals is therefore all that is necessary in criminal cases. The solution is treated with a slight excess of ammonia, sulphide of ammonium added, and the fluid, after being allowed to stand for several hours, filtered. The precipitate may consist of sulphide of zinc and hydrated oxide of chromium, as well as of traces of sulphide of iron and phosphate of lime. If the suspected materials contained achromate, this salt, in presence of hydrochloric acid and sulphuretted hydrogen, would be converted into sesquichloride of chromium a compound which is precipitated by sulphide of ammonium as a hydrated oxide.
The precipitate is washed with water, to which a little sulphide of ammonium is added, then dried, and fused with four times its weight of a mixture of equal parts of carbonate and nitrate of potassa. After the mass has remained in astate of fusion for a quarter of an hour, it is treated with boiling water, mixed with a little alcohol, in order to decompose the manganate that would be present were manganese contained in the materials under examination. The alcohol is then expelled by boiling the fluid, and the solution filtered. Thefiltratemay contain phosphate of potassa, originating from the phosphate of lime present, andchromate of potassa, resulting from the oxidation of the sesquioxide of chromium. In presence of the latter compound, the following reactions will occur in the solution: 1st., Upon acidulation with acetic acid and addition of solution of acetate of lead, a yellow precipitate, soluble in potassa, is formed; 2nd., if hydrochloric acid is added and sulphuretted hydrogen conducted into the solution, the latter acquires a green color, and, upon adding ammonia, a bluish-grey precipitate of chromic hydrate is produced; 3rd., if nitrate of silver is added to the solution, a brick-red precipitate is formed.
Theprecipitateremaining on the filter, may consist of zinc, mixed with the oxides of iron, nickel, cobalt, aluminium and manganese. It is dissolved in boiling hydrochloric acid, acetate of soda added, and the fluid boiled until no further precipitation occurs. The iron is now completely separated. The solution is then filtered, the precipitate washed, and an excess of potassa added to thefiltrate; if the solution contains cobalt, nickel or manganese—which is improbable—a permanent precipitate is formed. This is separated from the fluid by filtration: its further examination is, however, unnecessary, as the metals of which it consists are not poisonous. Thefiltratemay contain aluminium andzinc. The latter metal is detected by acidulating the filtrate with acetic acid, and adding a solution of sulphuretted hydrogen: in presence of zinc a white precipitate of its sulphide is formed.
In case organic substances are present, the precipitation of chromium by sulphide of ammonium may possibly have been hindered, and the metal have passed into the filtrate. When, therefore, chromium is not detected in the precipitate, the filtrate should also be examined. For this purpose, the fluid is evaporated to dryness, and the residue obtained fused with a mixture of nitrate and carbonate of soda. The fused mass is then taken up with water, the solution acidulated with acetic acid, and a solution of acetate of lead added: if chromium be present, a yellow precipitate, soluble in potassa, is produced.