82 Kansas Academy of Science. 



A NOTE ON THE DETECTION OF CYANIDES. 



By H. P. Cady, University of Kansas, Lawrence. 



^f^HE detection of cyanides in the presence of ferrocyanides, fer- 

 -*- ricyanides or sulfocyanates is complicated by the fact that 

 most'of the tests for the cyanides are not direct tests, but involve 

 the formation of ferrocyanides or sulfocyanates from the cyanides, 

 and, consequently, are not applicable in the presence of the above- 

 mentioned substances. 



Since hydrocyanic acid is both a very weak and an easily volatile 

 acid, it would seem that one ought to be able to separate the cyanides 

 from admixture with these other substances by making the solu- 

 tion containing them slightly acid and distilling off the hydrocy- 

 anic acid. Any of the well-known tests could then be applied to 

 the distillate. There is this difficulty, however, that ferro, and f erri- 

 cyanides and sulfocyanates will all yield hydrocyanic acid when an 

 acid solution containing them is distilled at the boiling tempera- 

 ture. Hilger and Tamba state that cyanides may be detected in the 

 presence of ferro- and ferricyanides by acidulating with tartaric 

 acid and passing a current of carbon dioxid through the solution, 

 taking care not to warm the solution above sixty degrees. On ac- 

 count of the restricted conditions this method is not adapted to use 

 by students. 



The cyanides are salts of very weak acid, while the ferro- and 

 ferricyanides and sulfocyanates are salts of strong acids ; as the re- 

 sult of this, the cyanides are, upon going into solution in water, 

 largely hydrolytically split up with the formation of much free 

 hydrocyanic acid, while the hydroferrocyanic acid, etc., are not 

 formed. As a result of this, hydrocyanic acid will distil from a 

 solution of potassium cyanide although the latter is highly alkaline. 

 The hydrolysis of all salts of weak acids is greater if there is pres- 

 ent at the same time in the solution the cations of some weak base ; 

 hence the hydrocyanic acid will distil much more readily from the 

 potassium cyanide solution if there be added to the latter some 

 ammonium chlorid. 



A very simple separation of the cyanogen ion from the interfer- 

 ing ions may be based upon the above. All that is necessary is 

 to make the solution alkaline with ammonium hydroxid, add some 

 ammonium chlorid, and distil at the boiling temperature. Under 

 these conditions the ferro-ferricyanides and the sulfocyanates are 



