DETECTION OF METALS.
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.
TREATMENT OF RESIDUE A.
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, and filtered.[K]
Sulphuric acid is added to the filtrate: if no precipitate forms, the absence of lead, 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 of silver.
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 with the 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.
TREATMENT OF FILTRATE B.
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.
TREATMENT OF PRECIPITATE a.
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 residue I. and the solution II. are separately examined as directed below.
RESIDUE I.
This may contain lead, mercury, tin, bismuth and antimony. It is heated for a considerable time with aqua 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 dissolves lead, but leaves tin as 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 of aqua regia on 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 for bismuth and copper, as in examination of precipitate III.
SOLUTION II.
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.
EXAMINATION OF PRECIPITATE c.
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 for arsenic. 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; the filtrate (IV.) is treated as directed below.
TREATMENT OF SOLUTION IV.
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 the solution introduced 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 in aqua regia and 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 with dilute hydrochloric acid, and the residue boiled with concentrated hydrochloric acid which dissolves the tin present. The fluid is filtered and the filtrate tested 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 the residue, 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 of copper, 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.
TREATMENT OF PRECIPITATE III.
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 of mercury is indicated; if, on the other hand, a residue is left, it is well washed, dissolved in aqua regia, and the solution examined, either by means of Smithson's pile, or in the apparatus of Flandin and Danger. (Vide [Detection 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 of bismuth. 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: if cadmium be 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.
TREATMENT OF SOLUTION b.
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 a chromate, 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 a state 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. The filtrate may contain phosphate of potassa, originating from the phosphate of lime present, and chromate 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.
The precipitate remaining 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 the filtrate; 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. The filtrate may contain aluminium and zinc. 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.
DETECTION OF ALKALOIDS AND SOME ILL-DEFINED ORGANIC SUBSTANCES.[L]
A general method for effecting the detection of alkaloids was first proposed by Stas. Since the publication of this method, modifications to it have been recommended by Otto, and by L. Uslar and J. Erdman. Other processes have been suggested by Rodgers and Girwood, by E. Prollius, and by Graham and Hofman. The latter will doubtless become general in their application; but up to the present time they have been employed exclusively in the detection of strychnine. Dialysis has also been recently applied in the separation of alkaloids.
STAS'S METHOD.
This method is based upon the facts: (a), that the acid salts of the alkaloids, especially those containing an excess of tartaric or oxalic acids, are decomposed by caustic alkalies and by the bicarbonates of soda and potassa; (b), that the alkaloids, when liberated in this manner, are combined with a certain amount of water which determines their solution in ether, although, in a desiccated state they may be insoluble in this menstruum; (c), that they may be extracted from their aqueous solutions by agitation with ether.
Stas's original method is as follows: The suspected substances, if organs are contained, are cut into fine shreds, then mixed with absolute alcohol, 0.5 to 2. grammes of tartaric or oxalic acid added and the whole introduced into a flask and heated at a temperature of 60° to 75°. When quite cold, the mixture is filtered, and the undissolved portion remaining on the filter washed with absolute alcohol, the washings being added to the filtrate. The alcoholic solution is evaporated, either by placing it under a bell-jar connected with an air-pump, or by passing a current of air, having a temperature not exceeding 35° over it, until reduced to a quarter of its original volume: the complete expulsion of the alcohol being then rendered certain. If insoluble matter separates during this operation, the concentrated fluid is passed through a moistened filter, the water used in washing the residue being united to the filtrate which is then evaporated to dryness by aid of the air-pump or by placing the fluid in a bell-jar over concentrated sulphuric acid. When the evaporation is completed, the residue is treated with absolute alcohol, the alcohol allowed to evaporate at the ordinary temperature of the air, and the second residue dissolved in the smallest possible amount of water. The fluid thus obtained is placed in a test-tube, and a concentrated solution of bicarbonate of soda added so long as effervescence takes place. Ether is then added, the mixture thoroughly shaken, and after it has remained at rest for some time, a small portion of the supernatant ether removed and evaporated on a watch-glass: the residue obtained will consist of the alkaloid present. Two cases are now possible: the alkaloid is a solid, or it is a liquid and is volatile.
The further treatment of the solution is modified according to these circumstances.
a. THE ALKALOID IS LIQUID AND VOLATILE.
If, upon the evaporation of the ether, oily streaks were left on the watch-glass, a volatile alkaloid is probably present.
In this case, a solution of caustic potassa is added to the test-tube, the mixture shaken, the supernatant ether decanted[M] into a flask and the remaining solution again washed with ether until the last portion fails to leave a residue upon evaporation. The etherial fluids are then united, and two cubic centimetres of water, acidulated with one-fifth of its weight of sulphuric acid, added. This acid retains the alkaloid, which is now in the state of a pure acid-sulphate soluble in water, the animal matters present remaining dissolved in the ether. The ether, in which some sulphate of conia may be contained—although the greater portion of this compound would remain in the aqueous solution—is then decanted. The remaining aqueous solution of the pure sulphate of the alkaloid is placed in a test-tube, a solution of caustic potassa and some ether added, and the mixture well shaken. The ether is next decanted and allowed to spontaneously evaporate in a dry place at a very low temperature, and the ammonia possibly present is then removed by placing the vessel containing the residue over sulphuric acid. The residue now obtained consists of the alkaloid present in a state of purity, and can be directly identified by means of the reactions described further on.
b. THE ALKALOID IS SOLID.
It sometimes occurs that ether fails to take up all of the alkaloid present in the fluid treated with bicarbonate of soda. Under these circumstances the fluid should be mixed with caustic potassa, the mixture shaken, and the ether decanted; this operation being repeated several times, until the entire amount of the alkaloid is removed; the ethereal fluids are then united in a capsule, and allowed to spontaneously evaporate. The result of the evaporation may be solid; more frequently, however, a milky liquid remains which restores the blue color to reddened litmus paper; if so, the presence of a vegetable alkaloid is certain. In order to purify the residue, a few drops of water, slightly acidulated with sulphuric acid, are added to the capsule, and the latter turned, so as to bring the fluid in contact with the substance at all points; in this manner a colorless and limpid fluid is obtained, the fatty substances adhering to the dish. The liquid is decanted into a second capsule, the remaining residue washed with a little acidulated water, and the washings likewise added to the principal solution. The fluid is now evaporated either in vacuo, or over sulphuric acid, to about three-fourths of its original volume a concentrated solution of neutral carbonate of potassa added, and the mixture treated with absolute alcohol, which dissolves the liberated alkaloid, and separates it from the sulphate of potassa formed and the excess of carbonate of potassa. The alcoholic solution is decanted and allowed to evaporate in vacuo or in the air: the alkaloid now crystallizes out in a state suitable for further examination.
MODIFICATIONS TO STAS'S METHOD, PROPOSED BY OTTO.
In Stas's method, the loss of morphine is possible, for, if ether is not added immediately after the addition of carbonate of soda, this alkaloid crystallizes and is then no longer soluble in that menstruum; and, if the ethereal solution is not quickly decanted, the portion dissolved will likewise separate out in small crystals. In both cases, morphine will remain in the aqueous solution from which the other alkaloids have been extracted by the ether. M. Otto recommends the addition of chloride of ammonium and a little soda-lye, in order to dissolve the alkaloid. Upon allowing the solution so obtained to stand for some time exposed to the air, crystals of morphine are deposited.
According to the same authority, it is advisable to omit the distinction drawn by Stas between volatile and fixed alkaloids, and submit both to the treatment recommended for those that are volatile.
Otto also recommends the agitation of the fluid containing the oxalates or tartrates of the alkaloids with ether, previously to their separation by means of bicarbonate of soda. By this treatment the elimination of the coloring matter present—as well as of colchicine, digitaline, picrotoxine, traces of atropine, and various impurities—is accomplished. As soon as the ether ceases to become colored and to leave a residue upon evaporation, alkali is added, and the operation concluded as usual. In this way the alkaloid is obtained, almost directly, in a pure condition. This last modification appears to us to be a very happy one, inasmuch as it greatly facilitates the purification of the alkaloid present.
MODIFICATIONS TO STAS'S METHOD, PROPOSED BY USLAR AND ERDMAN.
1st. The materials to be examined are brought to the consistence of a thin paste, and digested for about two hours with water, to which some hydrochloric acid has been added, at a temperature of 60° to 80°. The mixture is then filtered through a moistened linen cloth, and the residue washed with warm acidulated water; the washings being added to the solution.
2nd. Some pure quartz sand—or, preferably, silica prepared by the decomposition of fluoride of silicium—is added to the filtrate, the fluid supersaturated with ammonia, and evaporated to dryness over a water-bath: the addition of silica renders the residue friable.
3rd. The residue is boiled repeatedly with amylic alcohol, which extracts all the alkaloid present as well as the fatty and coloring matters, and the extracts filtered through filter paper that has been moistened with amylic alcohol.
4th. The filtered fluid is thoroughly agitated with ten or twelve times its volume of almost boiling water acidulated with hydrochloric acid: the hydrochlorate of the alkaloid present goes into the aqueous solution, the fatty and coloring substances remaining dissolved in the oily supernatant layer. The latter is separated by means of a pipette, and the acid aqueous solution shaken with fresh quantities of amylic alcohol until completely decolorized.
5th. The aqueous solution is then concentrated, ammonia added, and the mixture well shaken with warm amylic alcohol, in which the alkaloid dissolves. As soon as the solution forms a supernatant layer upon the surface of the fluid, it is drawn off with a pipette and evaporated on a water-bath. In this manner, the alkaloid is usually obtained in a sufficient state of purity to admit of its immediate identification; if, however, a small portion turns brown when treated with concentrated sulphuric acid, the process of purification must be repeated. Under these circumstances it is re-dissolved in dilute hydrochloric acid, the solution repeatedly shaken with amylic alcohol, in order to extract the impurities present, and the alkaloid then extracted with ammonia and amylic alcohol, as previously directed.
The method of von Uslar and Erdman differs from that of Stas merely in the substitution of amylic alcohol for ether, and of hydrochloric acid for oxalic or tartaric acid. It offers no advantages over Stas's method if the alkaloids present are soluble in ether but is even less advantageous in this case, inasmuch as its execution requires a longer time. In cases where the detection of morphine, or an unknown alkaloid, is desired, the use of amylic alcohol instead of ether is, it is true, preferable; still, with the exercise of care, ether can also be employed, and, as this process greatly facilitates examinations when no clew to the poison present exists and all alkaloids may possibly be absent, we prefer it to the one just described.
RODGERS AND GIRDWOOD'S METHOD.
This method—which as yet has only been employed in the detection of strychnine—is based upon the solubility of this alkaloid in chloroform. The substances under examination are digested with dilute hydrochloric acid, and the mixture filtered. The filtrate is then evaporated to dryness on the water-bath, the residue taken up with pure alcohol, the alcoholic solution evaporated, the second residue treated with water, and the solution so obtained filtered. The filtrate is next supersaturated with ammonia, and well shaken with chloroform, which, upon being separated by means of a pipette and evaporated, leaves the alkaloid in an impure state. Concentrated sulphuric acid is then poured upon the alkaloid: the latter is not affected by this treatment, whereas the foreign organic substances present are carbonized. After the lapse of several hours, the mixture is treated with water, the fluid filtered, and the strychnine extracted from the filtrate by means of ammonia and chloroform, as already described. The operation is repeated until the residue obtained by evaporating the chloroform is no longer affected by the treatment with sulphuric acid.
PROLLIUS'S METHOD.
The suspected substances are boiled with aqueous alcohol, mixed with tartaric acid, and evaporated at a gentle heat. The remaining aqueous solution is then passed through a moistened filter, ammonia added to the filtrate, and the mixture shaken with chloroform. The chloroform is separated, the last trace of the original solution removed by washing with water, three parts of alcohol added, and the fluid evaporated. If strychnine be present, it will now separate out in crystals. This method is applicable only in presence of a considerable quantity of strychnine, and is less serviceable than the one preceding.
GRAHAM AND HOFMAN'S METHOD.
This method, which is applied to the detection of strychnine in beer, is founded upon the fact that an aqueous solution of a strychnine salt yields the alkaloid to animal charcoal, from which it can be subsequently extracted by boiling with alcohol. The beer to be examined is shaken with 30 grammes of animal charcoal, and the mixture then allowed to stand twenty-four hours, with occasional shaking. The solution is next filtered, the animal charcoal washed with water, and boiled for half-an-hour with four times its weight of 90 per cent. alcohol. The apparatus represented in Fig. 12 is employed, in order to avoid a loss of substance in this operation.
Fig. 12.
The alcohol is filtered hot, evaporated, and the residue obtained treated with a small quantity of solution of potassa, and then agitated with ether. Upon spontaneous evaporation, the ethereal solution leaves the strychnine present in a comparatively pure state.
Macadam proposes to use this process for the detection of strychnine in animal bodies. For this purpose, the suspected materials are heated with a solution of oxalic acid, as in Stas's method, and the strychnine detected in the filtered solution in the manner just described. This method is scarcely to be recommended: the use of animal charcoal is doubtless serviceable in the examination of beer, as it effects the separation of a small amount of strychnine from a large quantity of fluid, but its application to other researches is much less to be advised.
APPLICATION OF DIALYSIS IN THE DETECTION OF ALKALOIDS.
In order to apply the dialytic method to the separation of alkaloids, the suspected substances are heated with hydrochloric acid, and the solution introduced into the dialyzer. The hydrochlorates of the alkaloids, being crystalline bodies, transverse the membrane, and are contained, for the greater part, after twenty-four hours, in the outer solution. The fluid is then concentrated, and the alkaloids either directly precipitated, or purified by one of the preceding methods.
IDENTIFICATION OF THE ALKALOID.
The alkaloid having been isolated by one of the preceding methods, it remains to establish its identity. Owing to the small number of reactions characteristic of organic compounds, this is a matter of considerable difficulty. There are two cases possible: the alkaloid may either be volatile or fixed.
THE ALKALOID IS VOLATILE.
In this case it may consist of nicotine, conine or aniline: less known alkaloids (piccoline, etc.) may also be present. We will confine ourselves to the consideration of the three first mentioned.
The alkaloid is divided into several portions which are placed on watch-glasses and submitted to the following tests:
a. A drop is treated with nitric acid: this may, or may not, impart a red tint to the alkaloid; if it does, another drop is treated with dry hydrochloric acid gas: if it assumes a deep violet color, it probably consists of conine.
b. In case a red color was not produced by the addition of nitric acid, another drop is treated with chloride of lime. If it acquires a violet tint, and two other drops, when heated, one with arsenic acid, the other with nitrate of mercury, become red, the body present consists of aniline.
or an homologous base.
c. Should the above tests fail to give positive results, and the substance, when treated with chlorine, assumes a blood-red color, and with hydrochloric acid does not change in the cold but turns to a deep violet color upon boiling, it probably consists of nicotine.
THE ALKALOID IS FIXED.
A very minute quantity is dissolved in the smallest possible amount of hydrochloric acid, and an excess of ammonia added. Three cases are now possible: (a) A precipitate, insoluble in an excess of the precipitant, is immediately formed; (b) a precipitate is formed, which, at first dissolves, but is subsequently deposited from the fluid; (c) no precipitate is produced, or, in case one forms, it dissolves in an excess of the precipitant and fails to separate out upon allowing the fluid to stand.
a. Ammonia produces a permanent precipitate.
A small quantity of an aqueous solution of carbonic acid is poured over the alkaloid in the water-glass, and notice taken whether it dissolves or not: in either case the mixture is evaporated on a water-bath to dryness, in order to avoid a loss of substance.
CARBONIC ACID FAILS TO DISSOLVE THE ALKALOID.
After the evaporation is completed, ether is added to the watch-glass: the alkaloid may, or may not, be dissolved. The ether is then evaporated at the ordinary temperature of the air.
Ether fails to dissolve the alkaloid.
It probably consists of berberine.
In this case, it will possess a yellow color, and its hydrochlorate will give a reddish-brown precipitate upon addition of sulphide of ammonia.
Ether dissolves the alkaloid.—A small portion is treated with nitric acid. If an intense green coloration is produced, the remaining portion is dissolved in ether, and an ethereal solution of oxalic acid added. If the precipitate now formed does not dissolve upon the addition of a little water, there is reason to suppose the presence of aricine.
Provided the addition of nitric acid did not produce a coloration, the mixture of the alkaloid and this acid is treated with a small quantity of sulphuric acid: if the fluid now acquires a red color, the substance probably consists of narcotine.
Should both nitric and sulphuric acids fail to cause a reaction, the alkaloid is dissolved in ether, precipitated by an ethereal solution of oxalic acid, and the precipitate treated with a little water. If it dissolves, it probably consists of papaverine.
CARBONIC ACID DISSOLVES THE ALKALOID.
The substance is treated with ether, notice being taken if it dissolves, which is evaporated at the ordinary temperature of the air so as to prevent a loss of minute portions of the alkaloid.
Ether dissolves the alkaloid.—If nitric acid gives first a scarlet, then a yellow color, sulphuric acid a yellow, changing to red and violet, and hydrochloric acid a violet color, the alkaloid present is probably veratrine.
If the above colorations are not produced, chlorine water is added to another portion of the substance, then ammonia; the formation of a green color, changing to violet and turning red upon a renewed addition of chlorine water, denotes the presence of quinine.
In case all of these tests give but negative results, and the alkaloid is soluble in concentrated sulphuric acid, a solution being formed which assumes a reddish-violet tint when stirred with a glass rod previously dipped in bromine water, the presence of delphine.
is indicated.
Ether fails to dissolve the alkaloid.—If the substance is capable of being sublimed,[N] it consists of cinchonine.
b. Ammonia produces a precipitate, which redissolves in an excess of the precipitant, but separates out after the lapse of an hour.
The substance is treated with cold absolute alcohol and its solubility in this menstruum noted. If it readily dissolves, it probably consists of brucine.
The presence of this alkaloid is confirmed by applying the following tests: (1) Nitric acid imparts a blood-red color to the substance; (2) if treated with sulphuric acid, it acquires a reddish tint which subsequently changes to yellow and green; (3) chlorine at first fails to cause a coloration, but after some time a yellow color which afterwards changes to a red is produced; (4) upon treating the substance with bromine, it immediately assumes a violet tinge.
In case the alkaloid is only slightly soluble in alcohol, there is reason to infer the presence of strychnine.
The following confirmatory tests should be applied: (1) If the substance is treated with a mixture of sulphuric acid and an oxidizing body, such as bichromate of potassa, binoxide of manganese, or peroxide of lead it acquires a violet color, which changes into red and finally passes into a clear yellow; (2) the addition of bichloride of platinum produces a precipitation of the hydrochlorate.
Should, however, the substance be only slightly soluble in alcohol, and the above reactions fail to take place, the presence of solanine.
is indicated. In presence of this alkaloid the following reactions will occur: (1) Upon treating the substance with concentrated sulphuric acid, it assumes a rose tint, which changes after some time has elapsed first to a deep violet, then to a brown color; (2) a solution of a salt of the alkaloid reduces gold and silver salts; (3) the addition of oxalic acid produces a precipitate in the aqueous and even acid solution of its salts.
c. Ammonia fails to produce a precipitate, or redissolves permanently the one formed.
The solubility of the alkaloid in ether is ascertained. If it be soluble, it may consist of aconitine, atropine or codeine; if insoluble, of emetine or morphine.
The alkaloid is soluble in ether.—If bichloride of platinum fails to precipitate the hydrochlorate from a neutral solution of the alkaloid, and sulphuric acid causes it to assume a yellow color which subsequently changes to a reddish-violet, it probably consists of aconitine.
In case bichloride of platinum causes a precipitate and sulphuric acid fails to produce the yellow coloration referred to above, the presence of either atropine or codeine is indicated. In order to decide which of these bases is present, the substance is dissolved in pure chloric acid and the solution allowed to spontaneously evaporate. If the alkaloid is deposited during this operation, it probably consists of atropine.
If this is not the case, there is reason to infer the presence of codeine.
The alkaloid is insoluble in ether.—If it dissolves in acetone it probably consists of emetine.
If acetone fails to dissolve it, the presence of morphine.
is indicated.
The following confirmatory tests should be applied: (1) Upon treating the substance with nitric acid, it acquires a blood-red color; (2) the addition of a solution of a persalt of iron produces an evanescent blue coloration; (3) chloride of gold is colored blue, when treated with the alkaloid; (4) the substance reduces iodic acid: this reduction is detected by adding to the acid a little starch-paste, which turns blue upon the liberation of the iodine; (5) permanganate of potassa, if heated with the substance, is reduced and acquires a green color.
IDENTIFICATION OF DIGITALINE, PICROTOXINE AND COLCHICINE.
It has already been remarked that in exhausting the first acid solution with ether—previous to the neutralization, according to Otto's method—colchicine, a weak alkaloid, digitaline, an indefinite mixture, picrotoxine (which appears to possess the properties of an acid), and traces of atropine, pass into solution.
The ether is evaporated on a water-bath to dryness, the residuary mass treated with slightly warmed water and the solution filtered from the undissolved resinous matter. The aqueous solution is next rendered feebly alkaline by addition of soda lye, and then well agitated with ether, until this fluid ceases to leave a residue upon evaporation. The ethereal solution is now decanted, and the water present removed by means of chloride of calcium. If it is evaporated, a residue containing the colchicine, digitaline and traces of atropine (mixed possibly with a minute quantity of picrotoxine, which is here left out of consideration) is obtained.
a. The alkaline solution, from which the ether has been removed, is acidulated with hydrochloric acid and again shaken with ether. The picrotoxine present is now dissolved, and upon dehydrating (by means of fused chloride of sodium) and evaporating the ethereal solution can be obtained in crystals. The crystals of picrotoxine are easily recognized by their forming in feathery tufts as well as by their length and silky brilliancy. Should crystals fail to form in a short time, it is advisable to take up the residue, left by the evaporations of the ether, with slightly warmed alcohol, and to allow the latter to spontaneously evaporate on a watch-glass, or, if the quantity of substance is exceedingly minute, on the slide of a microscope. After determining the form of the crystals, it should be ascertained that they possess an intense bitter taste and exhibit the other characteristic properties of picrotoxine. The following reaction is distinctive: If the crystals are dissolved in an aqueous solution of soda and a few drops of "Fehling's solution"[O] added, a reddish precipitate of cuprous oxide is formed.
b. Provided picrotoxine has not been found, the ethereal solution obtained by agitating the alkaline fluid with ether is to be examined for colchicine and digitaline. To this end, the residue obtained upon evaporating the solution to dryness is taken up with water, and the filtered fluid tested as follows: 1. It is ascertained if a drop of the solution possesses the bitter taste of digitaline. 2. Another drop is treated with solution of tannin; if either alkaloid be present, a precipitate is formed. 3. Two drops of the solution are next tested: one with tincture of iodine, the other with chloride of gold. These reagents precipitate colchicine, but do not affect solutions of digitaline or picrotoxine. Unfortunately traces of atropine, possibly present, would cause the same reaction; the test therefore fails to be conclusive. 4. Several portions of the solution are evaporated on watch crystals. Concentrated nitric acid is added to one portion: if colchicine be present, an evanescent violet coloration is produced, which changes to a light yellow upon addition of water, and to a pure yellow or reddish-orange color, if the mixture is saturated with a slight excess of caustic alkali. 5. Another portion of the residue is dissolved in a few drops of concentrated sulphuric acid, and the solution stirred with a glass rod moistened with bromine water: in presence of digitaline a violet-red color is produced. This coloration is more distinct when a small quantity of the alkaloid and an excess of sulphuric acid are present. 6. If a large amount of substance is at hand, the residue can be boiled with hydrochloric acid, and the green or brownish color and characteristic odor of digitaline produced, in case this body be present: this, however, is not a very delicate test. 7. Finally; it is advisable when the presence of digitaline is suspected to ascertain its physiological action. For this purpose, a minute quantity of the substance is placed upon the heart of a frog: in presence of the alkaloid, the pulsations are immediately retarded, or even arrested.
Although by means of the tests given above the existence of a special alkaloid, or of one of the ill-defined substances just mentioned, may be justly regarded as probable, its presence has not yet with certainty been demonstrated. This is especially true in cases where the compound possesses but few characteristic properties. When possible, the suspected substance should be obtained in a crystaline form, and then compared by aid of the microscope—if the small quantity present permits of no other examination—with crystals of the pure alkaloid, prepared under the same conditions.
In case 20 or even 10 centigrammes of substance are at hand, it is best to convert the alkaloid into its hydrochlorate, and evaporate the solution of this salt to dryness. The residue, after being weighed, is dissolved in water, and a solution of sulphate of silver added. The precipitate of chloride of silver formed is collected and carefully weighed, in order to calculate the weight of the chlorine contained in the hydrochlorate and consequently the molecular weight of the alkaloid. The filtrate from the chloride of silver, which contains the alkaloid in the state of sulphate, is treated with hydrochloric acid, to remove the excess of silver present and the fluid then filtered. The filtrate is next shaken with potassa and ether. Upon decanting and evaporating the ethereal solution, a residue consisting of the alkaloid present is obtained, which is then purified by crystallization from alcohol. An elementary analysis of the alkaloid is now executed. Certainty as to the presence of an individual alkaloid is attainable only when the execution of this confirmatory test is possible. The reactions previously described can be performed with fifteen centigrammes of substance, and this amount is sometimes contained in a cadaver. If but one or two centigrammes are at hand, it is still possible to detect the presence of an alkaloid; a conclusion, however, as to which cannot be arrived at, especially if the substance found is a liquid or an amorphous body, and one that presents few distinctive properties.
[III.
METHODS TO BE EMPLOYED, WHEN NO CLEW TO THE NATURE OF THE POISON PRESENT CAN BE OBTAINED.]
If poisoning has been caused by the administration of a mixture of numerous substances and these greatly differ in their properties, it is impossible to demonstrate in an incontestible manner the presence of each individual poison. This contingency fortunately but seldom arises; the criminal usually has recourse to one or two poisons, the detection of which is possible. It must not be imagined, however, that the presence of a poison in an organ can at once be detected with certainty by the mere application of a few tests; because, in searching for a substance which is absent, we may unwittingly destroy the one present, or, at least, transform it into combinations which would not allow of a definite conclusion as to its original condition.
In order to follow a systematic method in researches of this nature, it is advisable to divide the materials under examination into three parts: one portion is preserved, in order to ascertain its physiological effects on animals, the chemical analysis having failed to give positive results. The other portions are submitted to analysis, but with slightly different objects in view; one is subjected to a series of tests which are adapted, under all circumstances, to place the chemist on the track of the poison present, and which, in some cases, may even give conclusive and definite results. Should these tests furnish only indications of the nature of the poison, the remaining portion serves, with the assistance of this information, to establish beyond doubt the identity of the substance.