The object of the supplementary test of fulmination is to distinguish the oxalate of silver from the numberless other white precipitates which are thrown down by the nitrate of silver from solutions of other salts. The property of fulmination, which is very characteristic, requires, for security’s sake, a word or two of explanation, in consequence of the effect of heat on the tartrate and citrate of silver. The citrate when heated becomes altogether brown, froths up, and then deflagrates, discharging white fumes and leaving an abundant, ash-gray, coarsely fibrous, crumbly residue, which on the farther application of heat becomes pure white, being then pure silver. The tartrate also becomes brown and froths up, but does not even deflagrate, white fumes are discharged, and there is left behind a botryoidal mass, which, like the residue from the citrate, becomes pure silver when heated to redness. Another distinction between the oxalate and tartrate is that the former continues permanent at the temperature of ebullition, while the latter becomes brown. The preceding process or combination of tests will be amply sufficient for proving the presence of oxalic acid, free or combined, in any fluid, which does not contain animal or vegetable principles. 2. The only important modifications in the analysis rendered necessary 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.[395] 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.