By boiling a small quantity of atropine, say 1 mgrm., with 2 mgrms. of calomel and a very little water, the calomel blackens, and crystals may be obtained of a double salt; this reaction is, however, given also by hyoscyamine and homatropine. Mercuric potassium iodide solution, and mercuric bromide solution give amorphous precipitates, which, after a time, become crystalline, and have characteristic forms.
A solution of iodine in potassium iodide gives a precipitate with acidulated solutions of atropine in even a dilution of 1 : 10,000. Tannin precipitates, and the precipitate is soluble in excess of the reagent. If atropine be dissolved in dilute hydrochloric acid, and a 5 per cent. of gold chloride solution be added, a precipitate of a gold compound (C17H23NO3HClAuCl3) separates. The precipitate is in the form of rosettes or needles; melting-point 137°. On boiling it with water, however, it melts into oily drops, and this peculiar behaviour distinguishes it from the analogous salt of hyoscyamine, which does not melt in boiling water. The percentage of gold left on a combustion of atropine gold chloride is 31·35 per cent. 100 parts of the gold salt are equal to 46·2 of atropine. A platinum salt may also be obtained, (C17H23NO3HCl)2,PtCl4, containing 29·5 per cent. of platinum.
Vitali’s test is important; it consists in the production of a violet colour with alcoholic potash after oxidation.
The test may be applied as follows:—Equal parts, say 1 mgrm., of nitrate of sodium and of the substance to be tested, are rubbed together with a glass rod on a porcelain slab, and to this mixture 1 drop of sulphuric acid is added; the mixture is spread out in a thin film; upon this is strewn a little powdered potassium hydrate, and finally 1 drop of alcohol added; a violet colour is produced which passes into a fine red; according to the author of the test, 0·001 mgrm. of atropine sulphate can by this test be detected. Strychnine obscures this reaction.
Atropine, homatropine, and hyoscyamine show an alkaline reaction with phenolphthalein: atropine and homatropine give a precipitate with HgCl2. Hyoscyamine, not cocaine, precipitates HgCl2, and is alkaline to litmus, but not to phenolphthalein. Atropine behaves as follows:—(1) Sodium nitrate, sulphuric acid, and afterwards sodium hydroxide, gives a violet colour; (2) the test as before, but with nitrite instead of nitrate, gives orange colour, which, on dilution with sodium hydroxide solution, changes to red, violet, or lilac; (3) when heated with glacial acetic acid and sulphuric acid for a sufficient time, a greenish-yellow fluorescence is produced.—Flückiger, Pharm. Journ. Trans. (3), vol. xvi. p. 601-602.
The two alkaloids, strychnine and atropine, are not likely to be often together in the human body, but that it may sometimes occur is shown by a case recorded by L. Fabris.[488] A patient in the hospital at Padua had for some time been treated with daily injections of 3 mgrms. of strychnine nitrate; unfortunately, one day, instead of the 3 mgrms. of strychnine, the same quantity of atropine sulphate was injected, and the patient died after a few hours, with symptoms of atropine poisoning.
[488] Gazzetta, xxii., i. 347-350.
On chemical treatment of the viscera, a mixture of alkaloids was obtained which did not give either the reactions of strychnine or of atropine. To test the possibility of these alkaloids obscuring each other’s reactions, mixtures of 3 per cent. solutions (the strength of the injections) of atropine sulphate and strychnine nitrate were mixed together, and strychnine tested for by the dichromate and sulphuric acid test.