Page:Treatise on poisons in relation to medical jurisprudence, physiology, and the practice of physic (IA treatiseonpoison00chriuoft).pdf/176

 *cessary by the admixture of organic principles, occur in the case of the contents of the alimentary canal or vomited matters.

Dr. Coindet and I proved, that oxalic acid has not any chemical action with any of the common animal principles except gelatin, which it rapidly dissolves;—and that this solution is of a peculiar kind, not being accompanied with any decomposition, either of the acid or of the gelatin. Consequently oxalic acid, so far as concerns the tissues of the stomach or its ordinary contents, is not altered in chemical form, and remains soluble in water.

In such a solution, however, a variety of soluble principles are contained, which would cause abundant precipitates with two of the tests of the process,—sulphate of copper and nitrate of silver; so that the oxalates of these metals could not possibly be detached in their characteristic forms. The process for a pure solution, therefore, is inapplicable to the mixtures under consideration.

But changes of still greater consequence are effected on the poison by exhibiting antidotes during life. It is now generally known, that the proper antidotes for oxalic acid are magnesia and chalk. Each of these forms an insoluble oxalate; so that if either had been given in sufficient quantity, no oxalic acid will remain in solution, and the proofs of the presence of the poison must be sought for in the solid contents of the stomach or solid matter vomited.

The following process for detecting the poison will apply to all the alterations which it may thus have undergone.

Process for Compound Mixtures.—If chalk or magnesia has not been given as an antidote, the suspected mixture is to be macerated if necessary for a few hours in a little distilled water, then filtered, and the filtered fluid neutralized with carbonate of potass. If on the other hand chalk or magnesia has been given, the mixture is to be left at rest for some time, and the supernatant fluid then removed. This fluid, if not acid, may be thrown away; but if acid, it may be treated as already directed for a suspected mixture, where chalk or magnesia has not obtained entrance. After the removal of the supernatant liquid, pick out as many solid fragments of animal or vegetable matter as possible; and add as much pure water to the insoluble residue as will give the mass a sufficiently thin consistence. Add now to the mixture about a twentieth of its weight of carbonate of potass, and boil gently for two hours, or till the organic matter is all dissolved. While dissolution thus takes place, a double interchange is effected between the elements of the carbonate of potass on the one hand, and those of the earthy oxalate on the other, so that an oxalate of potass will at length exist in solution. The fluid when cold is next to be filtered, then rendered very faintly acidulous with nitric acid, then filtered and rendered very faintly alkaline with carbonate of potass, and filtered a third time. At each of these steps some animal matter will be thrown down.

From this point onwards the process proceeds in the same way, whatever may have been the original form in which the acid existed