138 Van Name — Estimation of Copper as Sulphocyanide 



Art. XII. — The Estimation of Copper as Cuprous Sulpho- 

 cyanide in the Presence of Bismuth, Antimony, Tin and 

 Arsenic ; by R. G-. Van Name. 



[Contributions from the Kent Chemical Laboratory of Yale University,— C VI.] 



It has long been known that copper may be quantitatively 

 separated from a number of other metals by precipitation as 

 cuprous sulphocyanide. The additional fact that this salt is 

 suitable for direct weighing as a means of estimating copper was 

 mentioned, apparently for the first time by Rivot* in 1854, and 

 was confirmed a quarter of a century later by the experiments 

 of Busse,f who employed the process for determining copper 

 not only alone but also in the presence of iron, nickel, zinc and 

 arsenic. Recent work by the present writer^ has shown that, 

 with the sole modification of filtering and weighing upon 

 asbestos, Rivot's method is accurate and satisfactory. 



In view of the tendency of bismuth, antimony and tin to 

 form insoluble basic chlorides in solutions containing only a 

 slight excess of hydrochloric acid, and the difficulty of obtain- 

 ing a complete precipitation of cuprous sulphocyanide in 

 strongly acid solutions, the estimation of copper by the above 

 method in the presence of these metals seemed to present 

 some difficulties. The following investigation, in which arsenic 

 was also included on account of its close relationship with the 

 above metals, was accordingly undertaken. 



The first series of experiments yielded the results given in 

 Table I, the method being as follows: A convenient quantity 

 of a copper sulphate solution of about \ normal strength was 

 measured from a burette, diluted, and acidified with a definite 

 amount of hydrochloric or sulphuric acid. If tartaric acid 

 was employed it was added at this point, after which the solu- 

 tion of arsenic, bismuth or antimony was introduced and the 

 copper finally precipitated by ammonium bisulphite and ammo- 

 nium sulphocyanide. Of the last a uniform amount, 70 cm9 of 

 a decinormal solution, was used for each experiment. The 

 ammonium bisulphite solution was prepared in the usual way 

 by passing sulphur dioxide into strong ammonia. 



Arsenic was introduced in the form of measured portions of 

 a standard arsenious acid solution which were made faintly 

 acid to litmus just before addition. Bismuth and antimony 

 were taken in the form of solutions of the chlorides in dilute 

 hydrochloric acid, the amount of acid thus introduced into 

 the determination being in all cases taken into account. 



* Compt. Rend., xxxviii, 868. f Zeitschr. anal. Chem., xvii, 53. 



X This Journal, vol. x, 451. 



