§ 267. =How long after Death can Hydric or Potassic Cyanides be Detected?=--Sokoloff appears to have separated prussic acid from the body of hounds at very long periods after death--in one case sixty days. Dragendorff recognised potassic cyanide in the stomach of a hound after it had been four weeks in his laboratory,[259] and in man eight days after burial. Casper also, in his 211th case, states that more than 18 mgrms. of anhydrous prussic acid were obtained from a corpse eight days after death.[260] Dr. E. Tillner[261] has recognised potassic cyanide in a corpse four months after death. Lastly, Struve[262] put 300 grms. of flesh, 400 of common water, and 2·378 of KCy in a flask, and then opened the flask after 547 days. The detection was easy, and the estimation agreed with the amount placed there at first. So that, even in very advanced stages of putrefaction, and at periods after death extending beyond many months, the detection of prussic acid cannot be pronounced impossible. [259] Dragendorff, G., _Beitr. zur gericht. Chem._, p. 59. [260] Casper’s _Pract. Handbuch der gerichtlichen Medicin_, p. 561. [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:--