(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.
DETERMINATIVE TESTS.
In many instances the tests we have termed indicative become determinative in their character. This is the case when the isolation of an alkaloid or a metal (unless mercury be found under the circumstances already mentioned) is accomplished; the results obtained are then conclusive. If, on the other hand,—not being able to separate either an alkaloid or a metal—upon saturating the originally acid fluid with potassa, or soda, the salts of these bases have been found in abundance, there is reason to infer that the poisoning has been caused by an acid; or, if, after the neutralization of the originally alkaline solution with an acid, potassa or soda are discovered in a large quantity, poisoning by an alkali is indicated.
In case the fluid is neutral, but more or less colored and odoriferous, and iodides or bromides are detected, we may justly suspect that the poisoning has been caused by the reception of iodine or bromine.
According to the indications furnished, iodine, bromine, one, or all of the acids, the caustic alkalies, etc., are then detected by means of the methods to be employed in cases where the expert has a clew to the poison present. In this manner, the presence of potassa and soda, and of bromine and iodine, even in mixtures, is easily ascertained. It only remains to mention the course to be pursued when suspicion exists that poisoning has been caused by the administration of a mixture of several acids. The suspected materials are boiled with water, and alcohol added to the solution in order to coagulate the animal matters. The solution is next filtered, the filtrate placed in a retort provided with a receiver and distilled until the residual portion acquires a pasty consistency. In this way, the acids present are separated into two classes: (a) those that are sufficiently volatile to have passed into the receiver, such as, acetic, nitric, hydrochloric and sulphuric acids (the latter acid will only be partially volatilized); and (b) those that remain in the retort. The former are detected by examining the distillate as previously directed.
The residue remaining in the retort is treated with absolute alcohol, the fluid filtered, and a solution of acetate of lead added to the filtrate: sulphuric, phosphoric and oxalic acids, if present, are precipitated. The precipitate is suspended in water and decomposed by means of sulphuretted hydrogen. The acids contained are now set free, and are detected by applying the tests already mentioned.