METHODS OF ANALYSIS 45 



Filter through a large folded filter. The titration is completed 

 by taking 500 cc. or an aliquot portion, adding 20 cc. H 2 S0 4 and 

 adding the standard KMn0 4 . 



The influence of the precipitate on the results is small. It 

 may be ascertained by testing a weighed portion of pure K 4 Fe(CN) 6 , 

 3H 2 0, adding the quantities of solutions as for an impure sample.* 



Impurities in commercial cyanide may be detected in the fol- 

 lowing rnanner.f Potassium cyanate will dissolve in alcohol of spe- 

 cific gravity 0.849, and this solution, on addition of hydrochloric 

 acid, will evolve carbon dioxide. Or, on adding water to the alco- 

 holic solution, and boiling off the alcohol, the liquid will give a 

 precipitate of calcium carbonate with calcium chloride. Cyanate 

 may also be detected by the following application of Blomstrand's 

 color-reaction: A strong solution of the sample is decomposed by 

 passing carbon dioxide through it until no more hydrocyanic acid 

 is evolved. By these means E. A. Schneider (Journal, Society 

 Chemical Industry, 1895, page 887) found that 3 grams of potas- 

 sium cyanide were decomposed in 45 minutes. To the resulting 

 liquid Schneider adds sufficient 95$ alcohol to precipitate the potas- 

 sium carbonate formed. The filtrate is then slightly acidified with 

 acetic acid, and some cobalt acetate solution added. An intense 

 blue color, due to the formation of the double cyanate of cobalt 

 and potassium, is produced, which renders easy the detection of 

 as little as 0.35$ of cyanate. If present in smaller quantities, more 

 of the cyanide must be taken, dissolved in the smallest possible 

 quantity of water, and the greater part of the cyanide precipitated 

 by the addition of absolute alcohol. The filtrate is then treated 

 with carbon dioxide, and tested as before. 



Chlorides may be detected by silver nitrate, added in excess, 

 which throws down silver cyanide as a white curdy precipitate. 

 They may be determined by Siebold's volumetric method. 



L. Siebold has shown that chlorides, when present, may be 

 conveniently determined in the same liquid in which the cyanide 

 has been estimated by neutralizing the excess of free alkali (which 

 should not be ammonia) by the cautious addition of dilute nitric 



* Quite a number of these methods are taken from a paper, entitled Analytical Work, in 

 connection with the cyanide process, by J. E. Clennell, read before the Inst, of Min. 

 and Met., London, May 21, 1903. 



+ Allen, Engineering and Mining Journal, August 15, 1903, page 239. 



