280 P. E. Browning — Separation of Copper from 



Aet. XLI. — On the Separation of Copper from Cadmium 

 by the Iodide Method; by Philip E Bkowningl 



[Contributions from the Kent Chemical Laboratory of Yale College — XXVHL] 



The separation of copper from cadmium by the precipita- 

 tion of the cuprous iodide by appropriate means has long been 

 known. Pisani* mentions the fact that potassium iodide can 

 be used to effect precipitations and claims that a satisfactory 

 separation can be made in this way. Flajolotf states that 

 potassium iodide cannot be used as a precipitant on account of 

 the solubility of cuprous iodide in that reagent, nor can hydri- 

 odic acid be employed if nitric acid is present. He recom- 

 mends that the solution containing copper be brought to acidity 

 with sulphuric acid, that a considerable excess of sulphurous 

 acid be added and that the precipitation be effected by hydri- 

 odic acid. Under this treatment he finds that only an un- 

 weighable or at least a very small trace of copper remains dis- 

 solved. Kohner^: in a paper of more recent date, in which he 

 reviews the various methods for the separation of copper from 

 cadmium, states that the iodide method is impracticable on 

 account of the solubility of cuprous iodide both in excess of 

 hydriodic acid and in potassium iodide. 



The work to be described was undertaken to determine if 

 possible under what conditions the method maybe safely used. 

 Solutions of copper and cadmium sulphates were made and 

 standardized by treating definite portions, measured from 

 burettes and weighed, by appropriate means, the average of 

 closely agreeing results being taken as the standard. A solution 

 of potassium iodide of approximately ten per cent strength, 

 was used throughout the work. The amount of the copper 

 solution generally taken (25 cm 3 ) contained about 0*12 grm. of 

 copper and the potassium iodide necessary to completely pre- 

 cipitate the iodide was about 0*6 grm. or 6 cm 3 of the solution. 

 I have in no case used less than 10 cm 3 or 1 grm. of the 

 iodide. In experiments (1) and (2) the free iodine separating 

 on the addition of the potassium iodide was bleached with 

 sulphurous acid and the cuprous iodide filtered off immediately. 

 In experiment (3) no sulphurous acid was added but the solu- 

 tion was boiled until a considerable amount of the free iodine 

 was expelled. In experiment (4) the boiling to expel the free 

 iodine completely was necessarily carried on until the solution 

 was evaporated nearly to dryness. Experiments (5) to (14) were 



* Compt. rend., xlvii, 294. 



f Journ. f. prakt. Chem , lxi, 105. 



% Zeitschr. Anal. Chem., xxvii, p. 203. Jour. Anal. Chem., vol. iii, p. 339. 



