222 POISONS : THEIR EFFECTS AND DETECTION. [§§ 273 , 274 . 
The estimation was in each case performed by titrating the distillate 
with argentic nitrate, the sulphur compounds having been previously 
got rid of by saturating the distillate with KHO, and precipitating by 
lead acetate. 
Venturoli 1 has, on the contrary, got good quantitative results with¬ 
out distillation at all. A current of pure hydrogen gas is passed through 
the liquid to be tested and the gas finally made to bubble through silver 
nitrate. He states that the whole of the hydric cyanide present is 
carried over in an hour. Metallic cyanides must be decomposed by 
sulphuric acid or tartaric acid. Mercury cyanide must be decomposed 
with SH 2 , the solution acidified with tartaric acid, neutralised with 
freshly precipitated calcic carbonate to fix any ferro- or ferri-cyanides 
present, and hydrogen passed in and the issuing gases led first through 
a solution of bismuth nitrate to remove SH 2 and then into the silver 
solution. 
§ 273. How long after Death can Hydric or Potassic Cyanides be 
Detected ?—Sokoloff appears to have separated prussic acid from the 
bodies 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, 2 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. 3 Dr E. Tillner 4 has recognised potassic cyanide in a corpse four 
months after death. Lastly, Struve 5 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. 
§ 274. 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 
1 L’Orosi, xv. 85-88. 
2 Dragendorff, G., Beitr. zur gericht. Chem., p. 59. 
3 Casper’s Pract. Handbuch der gerichtlichen Medicin, p. 501. 
4 Vierteljahrsschr. f. gerichtl. Med., Berlin, 1881, p. 193. 
5 Zeitschrift f. anal. Chemie, von Fresenius, xii. 4, 1973. 
