84 F. E. Beach — Use of Cupric Nitrate in the Voltameter 



It was found early in the course of the work that when the 

 nitrate solution was freshly prepared, it had a tendency to dis- 

 solve copper, and that this tendency which was due to the 

 solvent action of the solution itself or the presence of a small 

 quantity of free acid, decreased after the copper electrode had 

 been kept in the solution a sufficient length of time, and that 

 this latter effect seemed to be facilitated by the passage of the 

 current. On the other hand another difficulty to be contended 

 with was the oxidation of the copper deposited after the solu- 

 tion had been used too many times or the current was pushed 

 too far, causing in many cases a darkening or even perceptible 

 blackening of the metal. It was however discovered that the 

 blackening due to oxidation could be prevented by the addi- 

 tion of a small amount of ammonium chloride. 



Experiments were now made in which the current density 

 was varied through a considerable range with results which 

 are given in the following table : 



No. 

 1 

 2 

 3 

 4 

 5 

 6 

 1 

 8 

 9 



10 



11 



Solution. 

 Cu2N0 3 nearly neutral without NH 4 C1 



Cu2N0 3 with NH 4 C1, 



Current-Density 





amperes. 





cm' 2 Cu 



i.Eq. x 10 



31, 0-035 



3291 



0*065 



3291 



0-144 



3293 



0-024 



3293 



0-83 



3305 



0-114 



3290 



0-074 



3297 



0-076 



3298 



0-094 



3299 



0*019 



3290 



0*048 



3297 



These values show no dependence on the current- density 

 except No. 5 where the large value of the equivalent is best 

 accounted for by oxidation caused by the excessive current. 

 This deposit was badly fringed at the edge and easily detached. 

 Numbers 1-5, made by repeated use of the same solution, 

 show more uniformity than was at any other time obtained 

 from a solution without ammonium chloride present. Atten- 

 tion may be called to what appears to be evidence of the 

 neutralization of the solvent effect of the nitrate on the cop- 

 per in the gradual but not always regular increase iu the values 

 obtained from the same solution in successive experiments. 



Having now obtained a fair control of both the tendency to 

 oxidation and solution, experiments were next undertaken with 

 a view to determining the value of the electro-chemical equiva- 

 lent. With the exception of Nos. 1-5 already quoted, the 



