2. Sulphur Test, or Liebig‘s Test.—A second portion of the original mixture is placed in a beaker, and a watch-glass containing a few drops of bisulphide of ammonium is suspended over the liquid, the mouth of the beaker being closed. A short time is allowed to elapse; the watch-glass is then removed, and its contents evaporated to dryness at a low temperature. A blood-red colour is developed on the addition of a little perchloride of iron to the dry residue. This effect is due to the absorption of the hydrocyanic acid vapour by the bisulphide of ammonium—sulphocyanide of ammonium being formed, which, on the addition of perchloride of iron, gives the blood-red colour of the sulphocyanide of iron, which is bleached by corrosive sublimate.
3. Silver Test.—This is the most successful of the vapour tests, a single apple pip yielding all the reactions. If a watch-glass containing a few drops of nitrate of silver solution be suspended in a beaker (as in 2), the silver solution will become white and opaque, from the formation of cyanide of silver; examined under the microscope it is seen to consist of small prismatic crystals. The cyanide as formed, treated with hydrochloric acid, liquor potassæ, and sulphate of iron, will give Prussian blue.
The Quantitative Analysis.—Use the precipitate of cyanide of silver, 100 grains being equal to 20.33 of pure anhydrous acid.
Treatment.—The treatment of poisoning by prussic acid is now to be considered. As part of the general treatment, the stomach pump should be at once employed, and the stomach emptied and then washed out with water.
Ammonia.—The use of this substance was first advocated by Mr. John Murray of London, and is no doubt a valuable remedy if given early. Care should be taken that the mucous membrane of the air passages and alimentary canal be not inflamed by using too strong a solution.
Chlorine.—Recommended by Riauz in 1822. Water impregnated with the vapour of chlorine may be given internally, and the gas may be breathed under proper precautions.
Cold Affusion.—First proposed by Dr. Herbst of Göttingen. Its success is most to be looked for when it is employed before the convulsive stage of the poisoning is over. The cold water should be poured on the head and down the spine.
Fig. 39.—Photo-micrograph of crystals of cyanide
of silver obtained by the vapour test, × 50.
(R. J. M. Buchanan.)
Bleeding from the Jugular Vein.—In one case treated by Magendie, bleeding from the jugular vein was attended with success.