leg 



78 DETERMINATION OE COPPER. 



which might possibly affect the reaction, it seemed desirable to take up 

 the subject for further investigation. 



That the free copper influences the reaction is readily shown by the* 

 fact that the filtrate from the residue of Ag and H G Cu 4 N 2 Oi 2 contains 

 much nitrite of copper. 



More recently Wells* in a different connection has fully established i 

 the Hampe formula as representing the reaction between pure Cu 2 0. 

 and AgN0 3 . 



In all ordinary cases, such as the determination ofCu 2 in tough! 

 pitch metal, the determination of 0u 2 O in the native copper of Lakei 

 Superior by Monroe, t and the test cases, usiug Cu containing Cu 2 0, of' 

 Hampe, mentioned above, the unavoidable errors of the work are so i 

 great that it is immaterial whether the constant of solution is 28.8 or 

 33.33, but in the case of the series I had under investigation, where i 

 in one sample 8 percent, of Cu 2 was found by the Hampe constant, such 

 a difference could not be tolerated. 



For the purpose of this investigation, therefore, a series of samph 

 was prepared corresponding exactly with the material to which the 

 method would be applied ; that is, metallic copper containing Cu 2 0, but 

 containing a large amount of 0u 2 O. It was necessary that the samples 

 should contain nothing else. 



A tolerably pure CuS0 4 was dissolved iu hot water till a strong solu- 

 tion was obtained ; it was. however, neither boiling nor saturated. This ■ 

 solution was cooled with agitation, and a crop of small crystals ob- 

 tained. These were separated from the mother liquor, redissolved, and I 

 the operation repeated twice. The final crop of crystals gave an abso- 

 lutely pure CuS0 4 . 



A solution was made of the pure crystals, and the copper precipitated I 

 by the electric current. In order to obtain the copper in suitable form, . 

 the plan used in refining copper commercially by the current was 

 adopted. A strip of ordinary sheet copper was coated with paraffine 

 wax, and then graphite was sprinkled on it; this prepared strip was 

 used as the first cathode. When a thin film of copper had deposited, 

 the strip was taken from the bath, and the film of pure copper removed, , 

 the coating of wax making this quite easy to do. The thin sheet of pure i 

 copper was then used as the cathode, and the electrolysis of the solution i 

 continued, until a suitable amount of copper had been precipitated. 



In this way some 200 grams of absolutely pure copper were pre- 

 pared. 



This pure copper was next melted in a scorifier, in a gas muffle, and 

 allowed to absorb O from the air. In this operation the greatest care 

 had to be exercised to avoid contamination of the metal, especially by 



*H. L. Wells and S. L. Penfield. Gerhardite and Basic Cupric Nitrates, the chem- 

 ical work by the former. Am. Jr. Sci., Vol. xxx, p. 56. 

 tTrans. A. I. M. E., Vol. vill, p. 414. 



