INDICATIVE TESTS.
Two cases may present themselves: the materials to be examined possess either an alkaline (or neutral) or an acid reaction. As the methods to be pursued in either of these cases differ somewhat, they will be treated separately.
THE SUBSTANCE POSSESSES AN ACID REACTION.
The materials are mixed with water, placed in a retort provided with a delivery-tube which dips in a solution of nitrate of silver, and heated over a water-bath: if a cyanide be present, hydrocyanic acid will be disengaged, and a white precipitate of cyanide of silver formed: this is examined as previously directed (vide p. [50]).
In case a precipitate is not produced by the above treatment, more water is added to the retort, and the mixture boiled for about an hour, care being taken to collect the evolved vapors in a well-cooled receiver. The portion remaining in the retort is thrown on a filter and the filtrate obtained united with the distillate. The residue remaining on the filter is next washed with boiling absolute alcohol, the washings being added to the aqueous solution. In this way, the suspected substances are divided into soluble and insoluble portions, which are examined separately, as directed below.
a. LIQUID PORTION.
If the addition of alcohol caused a precipitation of animal matters, these are separated by filtering the solution. The filtrate is then placed under a bell-jar over concentrated sulphuric acid until its volume is considerably reduced. The solution may contain organic and inorganic bases and acids. In order to detect all bodies that are present, the following course is pursued:
(1). A current of sulphuretted hydrogen is conducted through the solution: the precipitation of some metals, usually thrown down by this gas, may fail to take place in this instance, owing to the presence of organic substances; however, some metals are precipitated, even in presence of organic compounds, and organic acids are but seldom present. In case a precipitate is formed, it is mixed with pure silica, collected on a filter, and treated with nitric acid. If the precipitate fails to dissolve, it is treated with aqua regia. In either case, the solution obtained is examined for metals by the ordinary methods.
(2). The solution in which sulphuretted hydrogen failed to produce a precipitate, or the filtrate separated from the precipitate formed, is divided into two parts: one portion is treated with ether and a solution of potassa; the other with ether and a solution of soda. Both mixtures are then well agitated, and notice taken if the ether dissolves any thing: if so, the operation is repeated several times until all soluble substances are removed. The ethereal solutions are next decanted and united, and then submitted to the examination for alkaloids as directed pp. [65]-[84].
(3). If—the above treatment giving either positive or negative results—a precipitate insoluble in ether is formed by the addition of potassa or soda, it is collected on a filter, washed, and dissolved in an acid. The solution is then tested for mineral bases.
(4). In case no definite result has been obtained by the preceding operations, one of the portions (for instance, the one to which potassa was added) is tested for the acids possibly present in the state of salts. The solution is divided into two parts (A and B) which are examined separately:
Portion A.—This is evaporated to dryness and the residue divided into four parts which are then tested for hydrofluoric, nitric, oxalic, and acetic and formic acids.
a. Hydrofluoric acid.—A portion of the residue is heated in a platinum crucible with sulphuric acid, and the crucible covered with the convex face of a watch-crystal coated with wax in which lines have been traced with a pointed piece of wood. If, after gently heating the crucible for some time and removing the watch-crystal, the lines traced in the wax are found to be etched in the glass, the substance under examination contains a fluoride.
b. Nitric acid.—If this acid be present, and a second portion of the residue is heated with sulphuric acid and copper, reddish-fumes are evolved. Upon conducting the vapors into a solution of sulphate of iron or narcotine, the reactions already mentioned in treating of nitric acid take place.
c. Oxalic acid.—The third portion of the residue is heated with sulphuric acid, and the evolved gas carefully collected. It should then be confirmed by an elementary analysis that the gas consists of equal volumes of carbonic oxide and carbonic acid. This test is not conclusive; it is also necessary to ascertain if the precipitate produced by the addition of a baryta solution (vide: under portion [B.]) produces the same reaction, inasmuch as other organic bodies could give rise to carbonic oxide and carbonic acid, and the danger of both admitting the presence of oxalic acid, when it is absent, and omitting its detection, in case it is present, would be incurred.
d. Acetic and Formic acids.—The fourth portion of the residue is distilled with dilute sulphuric acid. After determining that a small portion, previously neutralized with a base, acquires a red color, upon addition of a solution of a persalt of iron, the distillate is divided into two parts. One portion is treated with bichloride of mercury: if formic acid be present, metallic mercury is formed, with evolution of carbonic acid which produces turbidity in lime-water. The remaining portion of the fluid is digested, in the cold, with an excess of litharge: in presence of acetic acid, a soluble basic salt of lead, possessing an alkaline reaction, is produced.
[Portion B.]—The second portion of the solution is supersaturated with nitric acid, and this neutralized by addition of a slight excess of ammonia. The ammonia is then expelled by boiling the fluid, and a solution of nitrate of baryta added. If a precipitate forms, it is collected and subsequently examined for sulphuric, phosphoric, oxalic and boric acids as directed below. The filtrate is preserved and tested for hydrochloric, hydrobromic and hydriodic acids.
a. Oxalic acid.—A portion of the precipitate produced by the addition of nitrate of baryta is submitted to the test mentioned under the treatment of portion A.
b. Sulphuric acid.—If an insoluble residue remains upon treating the remainder of the precipitate with dilute hydrochloric acid, it consists of sulphate of baryta and indicates the presence of sulphuric acid.
c. Phosphoric acid.—An excess of solution of alum and ammonia is added to the portion of the precipitate dissolved in hydrochloric acid. If phosphoric acid be present, insoluble phosphate of alumina is precipitated. This is brought upon a filter: the filtrate being preserved and subsequently examined for boric acid. Upon boiling the precipitate with solution of silicate of potassa, silicate of alumina is thrown down, and phosphate of potassa remains in solution. Chloride of ammonia is now added to the liquid—in order to eliminate the excess of silica from the silicate—and the solution filtered. The filtrate is then tested for phosphates, by means of molybdate of ammonia (vide: detection of phosphoric acid, p. [48]).
d. Boric acid.—The filtrate from the precipitate of phosphate of alumina is evaporated to dryness, the residue mixed with sulphuric acid and alcohol, and the latter ignited. If the substance contains boric acid, the alcohol will burn with a green flame.
The filtrate, separated from the precipitate produced by the addition of nitrate of baryta, may contain hydrochloric, hydrobromic and hydriodic acids. In order to detect these compounds, some nitrate of silver is added to the solution, and the precipitate that may form carefully washed and decomposed by fusion with potassa. The mass is then dissolved in water, and the solution submitted to the following tests:
e. Hydriodic acid.—Some starch paste and nitric acid—containing nitrous acid in solution—are added to a portion of the solution: in presence of an iodide, the fluid immediately acquires a blue color.
f. Hydrobromic acid.—In case iodine has not been detected, chlorine water and ether are added to a second portion of the fluid, and the mixture well agitated. If bromine be present, the ether will assume a brown color. In case iodine is also contained in the fluid, and the detection of bromine is desired, it is necessary to acidulate the solution with hydrochloric acid, and then shake it with chloride of lime and bisulphide of carbon. The bisulphide of carbon dissolves the iodine, acquiring a violet color, which disappears upon a renewed addition of chloride of lime; whereas, in presence of bromine an orange coloration remains, even after the disappearance of the iodine reaction.
g. Hydrochloric acid.—Since the substance under examination will already contain hydrochloric acid, it is unnecessary, in most cases, to institute a search for this compound. Nevertheless, it may be well to take a quantity of the solution, corresponding to a known weight of the original substance, and precipitate the acid by adding nitrate of silver. The precipitate formed is dried and weighed. It is then heated in a current of chlorine, in order to completely convert it into chloride of silver, and its weight again determined. Only in case the amount of chloride found is very large, is it to be inferred that the poisoning has been caused by hydrochloric acid.
h. Hydrosulphuric acid.—(Sulphuretted hydrogen). If the precipitate produced by nitrate of silver possesses a black color, it may consist of a sulphide. Upon treating a portion with solution of hyposulphite of soda, all but the sulphide of silver is dissolved. In case a residue remains, it is calcined with nitrate of soda, and the sulphate formed detected by adding a soluble barium salt to its solution.
Sulphates, chlorides, carbonates and phosphates are most frequently met with in the preceding examination, and it should be carefully noticed which of these salts exist in the greatest abundance. If acids of comparatively rare occurrence (such as the oxalic and tartaric) are found, their approximate amount is also to be noted. These facts, together with the original acidity of the materials and the absence of other toxical bodies, would lead to the conclusion that the poisoning was caused by the reception of an acid, as well as to the identification of the special acid used. In subsequently effecting the detection of the poison by the determinative tests, the danger of destroying other poisons possibly contained in the substance will be obviated, as the question of the absence or presence of these latter will have been previously decided.
(5). The examination for acids concluded, the various fluids which have accumulated, and from which the acids present have been separated, are united and the whole evaporated to dryness. The organic substances, present in the residue obtained, are destroyed by means of nitric acid, and the residual mass examined for soda. If this substance has not been introduced into the portion of fluid examined, and is discovered in a quantity largely in excess of the amount normally contained in the organism, it is probable that poisoning has been caused by its administration, and that an acid has also been given, either in order to mask the poison, or to act as an antidote. In this case, it is necessary to carefully search for acetic acid, as this is the substance usually employed as an antidote for alkalies.
(6.) Whatever results have been obtained by the preceding examinations, the portion of the fluid which has been treated with soda (vide p. [87]) is evaporated to dryness. The organic matters possibly present are destroyed by means of nitric acid, or aqua regia, and the residue taken up with water. The solution so obtained is then examined for metals (including potassa, which salt has not been introduced into this portion of the fluid in any of the preceding operations) by the usual methods.
(7). The soluble portion of the suspected materials having been thoroughly tested, the undissolved substances remaining on the filter are next examined.
b. SOLID PORTION.
(1). The organic matter present is first destroyed by treatment with aqua regia. The fluid is then evaporated to dryness, and the residue heated until the nitric acid is entirely expelled; the escaping vapors being collected in a cold receiver. The residue is next taken up with water, the solution filtered, and sulphuric acid added. Should a precipitate of sulphate of lime, sulphate of baryta or sulphate of strontia form, it is separated from the fluid and further examined. The filtered solution is then introduced into Marsh's apparatus, sodium amalgam being employed for generating the hydrogen, and tested for arsenic and antimony by means of the reactions previously given.
(2). Whether one of the above poisons be discovered or not, the still acid fluid is removed from the flask, a current of chlorine conducted through it for several hours and the solution then examined for mercury by Flandin and Danger's method. In case mercury is found it could scarcely have originated from the metal in Marsh's apparatus, as this would not be attacked by cold dilute sulphuric acid: however, to remove all doubts, the test should be repeated with a portion of the substances reserved for the examination by the determinative tests.
(3). Whatever have been the results of the above examinations, it is still to be ascertained if the fluid, which has been successively treated by Marsh's and Flandin and Danger's methods, does not contain other metals. This is accomplished by means of the ordinary reactions.
THE SUBSTANCE POSSESSES A NEUTRAL OR AN ALKALINE REACTION.
The examination is conducted in precisely the same manner as in the preceding case, excepting that the materials are first acidulated with oxalic or tartaric acids. Particular attention should be given to the search for soda, potassa, lime, baryta and strontia, and the determinative tests subsequently applied according to the indications obtained.