[261] Vierteljahr. f. gerichtl. Med., Berlin, 1881, p. 193.
[262] Zeitschrift f. anal. Chemie, von Fresenius, 1873, xii. p. 4.
§ 268. Estimation of Hydrocyanic Acid or Potassic Cyanide.—In all cases, the readiest method of estimating prussic acid (whether it be in the distillate from organic substances or in aqueous solution) is to saturate it with soda or potash, and titrate the alkaline cyanide thus formed with nitrate of silver. The process is based on the fact that there is first formed a soluble compound (KCy, AgCy), which the slightest excess of silver breaks up, and the insoluble cyanide is at once precipitated. If grains are used, 17 grains of nitrate of silver are dissolved in water, the solution made up to exactly 1000 grain measures, each grain measure equalling ·0054 grain of anhydrous hydrocyanic acid. If grammes are employed, the strength of the nitrate of silver solution should be 1·7 grm. to the litre, each c.c. then = ·0054 hydrocyanic acid, or ·01302 grm. of potassic cyanide.
Essential oil of bitter almonds may also be titrated in this way, provided it is diluted with sufficient spirit to prevent turbidity from separation of the essential oil. If hydrocyanic acid is determined gravimetrically (which is sometimes convenient, when only a single estimation is to be made), it is precipitated as cyanide of silver, the characters of which have been already described.
§ 269. Case of Poisoning by Bitter Almonds.—Instances of poisoning by bitter almonds are very rare. The following interesting case is recorded by Maschka:—
A maid-servant, 31 years of age, after a quarrel with her lover, ate a quantity of bitter almonds. In a few minutes she sighed, complained of being unwell and faint; she vomited twice, and, after about ten minutes more had elapsed, fell senseless and was convulsed. An hour afterwards, a physician found her insensible, the eyes rolled upwards, the thumb clenched within the shut fists, and the breathing rattling, the pulse very slow. She died within an hour-and-a-half from the first symptoms.
The autopsy showed the organs generally healthy, but all, save the liver, exhaling a faint smell of bitter almonds. The right side of the heart was full of fluid dark blood, the left was empty. Both lungs were rich in blood, which smelt of prussic acid. The stomach was not inflamed—it held 250 grms. of a yellow fluid, containing white flocks smelling of bitter almond oil. In the most dependent portion of the stomach there was a swollen patch of mucous membrane, partially denuded of epithelium. The mucous membrane of the duodenum was also swollen and slightly red. The contents of the stomach were acid, and yielded, on distillation, hydride of benzole and hydric cyanide. Residues of the almonds themselves were also found, and the whole quantity taken by the woman from various data was calculated to be 1200 grains of bitter almonds, equal to 43 grains of amygdalin, or 2·5 grains of pure hydric cyanide.