CHEMICAL SCIENCE. 225 



NEW PROCESS FOR THE DETERMINATION OF COPPER IN MIN- 

 ERALS AND ARTIFICIAL PRODUCTS, BY M. RIVOT. 



The author having found that all the principal processes for the determina- 

 tion of copper in minerals and alloys were liable to error, has adopted a new 

 method, which is founded on the insolubility of the sulpho-cyanide of copper 

 Cy S 2 Cu-, and the great solubility of the sulpho-cyanides of all the other 

 metals in acid fluids. It consists in the three following operations : 



1. All the metals contained in the substance under examination are dis- 

 solved in hydrochloric acid, avoiding the use of oxyclating agents. 



2. The salt of copper is brought to a minimum by means of a reducing 

 agent (hypo-phosphorous or sulphurous acid), and a dilute solution of sulpho- 

 cyanide of potassium is poured into it; this immediately precipitates the 

 copper alone. 



3. The metal is determined by drying the sulpho-cyanide thus obtained at 

 a moderate heat. The determination may be checked by converting the 

 sulpho-cyanide into sulphuret of copper by fusion with a little sulphur in a 

 porcelain crucible, from which the air must be excluded. 



This process may be simplified when the substance to be examined contains 

 no metals (besides copper) precipitated by sulphuretted hydrogen. In this 

 case the solution of ah 1 the metals is afiected by muriatic acid, and the copper 

 precipitated by sulphuretted hydrogen. The precipitate is converted into 

 sulphuret of copper by fusion with a little sulphur. Comptes Eendus, p. 865, 

 1854. 



SEPARATION OF COBALT FROM NICKEL. 



Liebigjias found that when a current of chlorine is passed into a cold solu- 

 tion of the double cyanides of cobalt and potassium and of nickel and potas- 

 sium, the liquid being kept alkaline by the addition of caustic soda or potash, 

 the nickel is complete!}' converted into sesqui-oxyd and precipitated, while the 

 cobalt remains hi solution as unaltered double cyanid. The sesqui-oxyd of 

 nickel may be washed and ignited, and the nickel weighed in the form of 

 protoxyd ; it is perfectly free from cobalt. The solution, after passing the 

 chlorine, must still be alkaline. The smallest trace of nickel gives an inky 

 black color when dissolved in cyanid of potassium, and treated with chlorine. 

 This method of separating cobalt and nickel has, perhaps, some advantages 

 over Liebig's second method, which, it will be remembered, consists in boiling 

 double cyanids with oxyd of mercury, which precipitates the nickel but not 

 the cobalt. 



IODO-NITRATE OF SILVER. 



This substance, the active principle in the collodion photographic process, 

 has been found to be a definite compound of the iodide and the nitrate of 

 silver, its composition being represented by Ag 0, NO 5 -f- Ag I; it is 

 blackened on exposure to light much more rapidly than either of its ingredients 

 alone. It is unaffected by and insoluble in absolute alcohol, but is decom- 



10* 



