in the Presence of Bismuth^ Antimony, etc. 141 



Antimony is affected to a much greater extent than bismuth 

 by the presence of the tartaric acid, so that if enough of the 

 latter is present, relatively little hydrochloric acid is required 

 to hold the antimony in solution. As the amount of the tar- 

 taric acid is practically without effect upon the precipitation of 

 the copper, these conditions are favorable for the process. 

 Experiments 26 to 31 give the results obtained in the presence 

 of antimony, which show that the process is practicable. 



In all the experiments thus far described the excess of 

 ammonium sulphocyanide above the amount theoretically 

 required has been comparatively small, 70 cmS of the decinormal 

 solution having been employed where the theory called for 

 about 50 cm3 . It has been elsewhere shown * that increase in 

 the amount of the sulphocyanide diminishes the effect of the 

 hydrochloric acid present. This fact has an important appli- 

 cation in the separation of copper from bismuth, because it is 

 possible, even when the solution contains an excess of hydro- 

 chloric and tartaric acid above the amount required to keep the 

 bismuth in solution, to precipitate the copper completely by 

 employing a sufficient quantity of ammonium sulphocyanide. 

 By working in this way in solutions more strongly acid than 

 would otherwise be consistent with accuracy, an additional 

 advantage is gained because the consequent retardation of the 

 precipitation produces precipitates which can be more easily 

 filtered than those obtained from neutral or less acid solutions. 



For the experiments of Table II the precipitation was car- 

 ried out in the manner just described, and as the quantity of 

 copper employed in the previous determinations had proved 

 rather too large to be conveniently filtered and washed in a 

 crucible of the ordinary size, a smaller amount was taken. A 

 new copper sulphate solution of about -fa normal strength was 

 employed, the other solutions being the same previously used. 



The results obtained with bismuth are given in experiments 

 1 to 8. For this amount of copper the theory requires about 

 12*5 cm3 of the decinormal ammonium sulphocyanide, but owing 

 to the amount of acid present the results are low until about 

 125 cm3 are added, beyond which point further increase produces 

 no effect. Carried out in this way the separation from bis- 

 muth is satisfactory and the results accurate. 



Tin in the higher condition of oxidation may be success- 

 fully treated in the same manner as experiments 9 to 11 show. 

 Tartaric acid is of material assistance in reducing the amount 

 of hydrochloric acid necessary to hold the tin in solution, 

 whether in the stannic or stannous state. 



The estimation of copper in the presence of tin in the 



* This Journal, vol. xiii, p. 23. 



