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Detection of hydrocyanic acid in traces. By Thos. C. Van Nivs and 

 Sherman Davis. 



The detection of HCN in traces in the presence of hydroferro- and hydro- 

 ferricyanic acid, according to the method of Otto, is attended with many 

 difficulties. In our laboratory practice we have failed to find it suffi- 

 ciently delicate and reliable. The distillation at 50, 60, or even at 

 80 per cent, often fails to drive over the free hydrocyanic add. As a sub- 

 stitute for this method we cheerfully recommend the following method : 



I. When a large quantity of organic matter in a coar.se condition is 

 present, introduce it into a fine-meshed silk seive. Moisten it all over 

 with a 10 per cent. sol. tartaric acid and wash into a 500cc. cylinder, glass 

 stoppered, with distilled water, until the total vol. amounts to 200-250(C. 

 If the organic matter is very finely divided, introduce the substance at 

 once into the cylinder, dilute with water to 200cc. Make acid with a 10 

 per cent. sol. tartaric acid, add lOOcc. ethyl ether, and shake the mixture 

 for some time. Let the ether separate and pipette it off into an evapor- 

 ating dish. Eepeat the process of extracting with the ether, the second, 

 and if necessary, the third time, using smaller quantities of ether. Unite 

 the ether extracts. Render the ether sol. slightly alkaline with an alco- 

 holic solution of KOH, stir very thoroughly, and allow the ether to evap- 

 orate spontaneously. This leaves the trace of hydrocyanic acid in combi- 

 nation with potash, as, a fixed salt. Transfer the residue from the ether 

 extract to a large test tube. The tube should be provided with a stopjier 

 with double perforations. Through one pass a veil fitting glass tube, and 

 terminate it at the under surface of the cork ; through the other perfora- 

 tion pass a well fitting glass tube whose lower end is drawn out to a very 

 fine point, and let it extend to the bottom of the test tube. Connect the 

 tube which teaches to the bottom of the test tube with a hydrogen gener- 

 ator. The other and shorter tube is connected with a Liebig'sbulb con- 

 taining 25cc of a mixture of 3 pts. of yellow amononia sulphid and one pt. 

 NHjOH. Make the ether residue in the test tube acid with tartaric acid. 

 Make the connections as above described, and pass a slow stream of hy- 

 drogen through the sol. for 30-45 min. Break the connection after the gas 

 has passed sufficiently long, transfer the am. sulphide sol. to a large 

 watch glass, and allow it to evaporate high over a free flame. By this pro- 

 cess the hydrocyanic acid which passes over with the hydrogen gas is 

 transformed into am. sulphocyanate. When the am. sulphide sol. has 

 been completely decomposed by evaporation, take up w'ith distilled water 



