144 Van Name — Estimation of Copper as Sulphocyanide. 



separate copper from unknown quantities of bismuth, or from 

 mixtures containing bismuth, the procedure would be as fol- 

 lows : Having the copper and bismuth in hydrochloric acid solu- 

 tion, add tartaric acid and, after diluting if necessary, determine 

 by blank tests with small aliquot portions of the solution how 

 much ammonium bisulphite can be added to the whole without 

 precipitating the bismuth. Then keeping the bisulphite well 

 within this limit, carry out the precipitation of the copper as 

 already described, using a considerable excess of ammonium 

 sulphocyanide. Where bismuth is absent, antimony and tin 

 could be treated in the same way, but the latitude possible in 

 the adjustment of the conditions is so much greater with these 

 metals that preliminary tests would usually not be needed. 

 For the separation from arsenic no precautions are required 

 beyond a reasonable degree of acidity of the solution. 



The writer is under obligation to Prof. F. A. Gooch for his 

 kind advice and helpful suggestions. 



