[E] The effervescence of the mixture is prevented by slowly adding the arsenical solution to the generating flask. In order to avoid loss of arsenetted hydrogen, the cold dish should be directly applied to the flame even before the introduction of the suspected solution, and its position changed at short intervals, so as to allow the deposit to be formed on different parts.—Trans.
[F] Owing to the impurities often occurring in zinc, the use of distilled magnesium in Marsh's apparatus has also been suggested. This metal is now to be obtained in a state of great purity; it is, however, sometimes contaminated with silicium, which body likewise gives rise to a metallic deposit, but one that is readily distinguished from arsenical spots by its insolubility in nitric acid, aqua regia, and in hypochlorite of soda. The presence of magnesium causes the precipitation of the non-volatile metals possibly contained in the fluid tested for arsenic.—Trans.
[G]The omission in the text of Reinsch's test should be supplied. This test is based upon the fact that when solutions of arsenious acid or an arsenide are acidulated with hydrochloric acid and boiled with metallic copper, the latter becomes covered with a film consisting largely of metallic arsenic: it is extensively employed in chemico-legal examinations. The materials to be examined are completely disintegrated by boiling with hydrochloric acid, and the fluid filtered. Some pure copper gauze or foil, having a polished surface, is then immersed in the boiling solution, and notice taken of the formation of a grey deposit. If a coating be formed, fresh pieces of the metal are added, so long as they become affected. The copper is then withdrawn from the solution, thoroughly washed with water, and dried, either by means of the water-bath or by pressing between bibulous paper. It is next introduced into a dry tube, and heated over a spirit lamp. The arsenic present volatilizes and is oxidized to arsenious acid which forms a deposit, consisting of octahedral crystals, on the cold part of the tubes. These are subsequently tested by means of the reactions distinctive of arsenious acid. It need hardly be added that the absolute purity of both the hydrochloric acid and of the copper is to be carefully established. The deposit obtained in the above operation was formerly regarded as pure arsenic, but it has been proved to be an alloy consisting of 32 per cent. arsenic, and 68 per cent. copper. Reinsch's test possesses the advantage of requiring but little time for its execution, of being applicable to complex organic mixtures, and of effecting the detection of a very minute trace of the poison.—Trans.
[H] Ferrocyanides and ferricyanides—non-poisonous compounds—likewise, evolve hydrocyanic acid when distilled with a strong acid. Their presence is indicated by stirring a small portion of the materials with water, filtering the fluid, acidulating the filtrate with hydrochloric acid, and testing two portions: one with sesquichloride of iron, the other with protosulphate of iron. If either of the above salts be present, a blue precipitate is produced.—Trans.
[I] Baryta and strontia dissolve in alcohol, but only when they are anhydrous and the alcohol is absolute, which is not the case here.
[J] The so-called "chloride of lime" is probably either a mixture of chloride and hypochlorite of calcium or an oxydichloride of the metal; "Eau de Javelle" is the corresponding potassium compound.—Trans.
[K] If an insoluble residue remains by the treatment with nitric acid, it may consist of tin. In this case, it is dissolved in aqua regia, the metal precipitated by immersing a plate of zinc in the solution and then re-dissolved in boiling hydrochloric acid. Upon adding chloride of gold to the solution so obtained, a purple precipitate is formed. Sulphuretted hydrogen produces a brown precipitate, soluble in sulphide of ammonium, in presence of tin.
[L] Colchicine, picrotoxine and digitaline.
[M] The necessity of decanting etherial and other solutions is advantageously obviated by the use of a pipette.—Trans.
[N] Cinchonine, when sublimed, condenses in minute brilliant needles.—Trans.