as its detection in stains; and indeed a sure and delicate process is still a desideratum in medico-legal chemistry. The process varies, as in the case of sulphuric acid, according as the subject of analysis is acid or neutral.
a. If the mixture be acid, and the proportion of the acid considerable, it maybe detected without difficulty. It is merely necessary to ascertain the acidity of the mixture by litmus-paper, to neutralize with potass, water being added if necessary, and then to filter and evaporate to a convenient degree of concentration. Crystals will form on cooling, which may be decomposed by sulphuric acid in the usual way. But the medical jurist ought not to flatter himself with the expectation of meeting often with a proportion large enough to admit of being discovered by so coarse a method of analysis. In general the crystallization of the nitrate of potass is prevented by co-existing animal or vegetable matter. When the proportion appears inconsiderable, therefore, a different process must be pursued. In preparing the former edition of this work, the present topic was investigated with some care, and a method suggested which appeared to me at that time more effectual, delicate, and conclusive than any previously made public. Since then Professor Orfila has also investigated the subject attentively, and after trying various methods, has ended in adopting one which is substantially the same as that now referred to, but without a precaution, which seems to me essential for success in certain probable enough circumstances.[1] I am therefore disposed to retain my former process, with some variations and additions in the details.
Macerate the subject of analysis for a few hours in distilled water, if it be not already liquid enough; and then boil for a few minutes, and filter it. Ascertain now whether the fluid be acid to litmus; and if it be so, neutralize it with solution of potash, or as Orfila suggests, with a solution of the purer salt, the bicarbonate of soda. Evaporate gently, to obtain crystals if possible; and if these do not tend to the cubical form, distil them with sulphuric acid, and proceed as directed for nitric acid simply diluted. If crystals do not appear, or their form tend to the cube,—in which case chloride of sodium is present,—re-dissolve the whole residue of evaporation in distilled water; add a slight excess of a warm solution of acetate of silver, to throw down organic matter and the chlorine of any chlorides that may be present; filter and evaporate to dryness, and distil the residuum with sulphuric acid, applying as usual to the vapour the tests of litmus-paper and morphia,—also, as Orfila proposes, the solution of narcotin in sulphuric acid, and proto-sulphate of iron in water,—and if the quantity of vapour be great enough, the sense of smell and the action of copper with the condensed vapour.
b. If the mixture be neutral, proceed exactly as above, except that it becomes unnecessary to neutralize the liquid with potash or bicarbonate of soda. This variety in the process will be principally required, where earths or alkalis have been administered as antidotes.
- ↑ Annales d'Hygiène Publique, &c. xxviii. 200. Also Toxicologie Génerale. 1843, i. 142.
