400 Mr. T. Gray on the Electrolysis 



No copper will be left on the blotting-paper, and no oxidation 

 will take place if the deposit is of average quality. If the 

 plate has been too small for the current, the drying in the 

 blotting-paper may have to be omitted; and in that case it 

 will be found advantageous to dip the plate in alcohol or 

 ether before drying, as it then dries more quickly and is less 

 likely to be oxidized. The plate should never be raised to a 

 temperature so high that it cannot be held comfortably in the 

 fingers, and evaporation should be, if possible, promoted by 

 holding it in a rapid current of dry air. This latter treat- 

 ment is that best suited for the loss plates, as they can 

 seldom be placed in a blotting-pad without removing copper; 

 after a little practice, however, it is not difficult to dry with- 

 out oxidizing them ; at the same time it does not seem 

 advisable to make use of the loss plates for ordinary 

 purposes. 



Loss of Weight in the Solution. — A number of ex- 

 periments were made on the effect of leaving silver plates 

 in solutions of silver nitrate, and copper plates in solutions 

 of copper sulphate, for the purpose of finding the rate of loss 

 of weight in these circumstances. The solutions of silver 

 nitrate contained from five to thirty per cent, of the salt, and 

 were in all cases pure with no acid added. The plates were 

 pure silver sheet. There was no appreciable change of weight. 

 The solutions of copper sulphate varied in density from 1/2 

 to 1*05, and were partly made from pure copper sulphate and 

 distilled water with no acid added, and partly from this solu- 

 tion with from one to twenty per cent, of ordinary commercial 

 sulphuric acid added. The copper plates were in some of the 

 experiments ordinary "high conductivity " sheet copper, and 

 in others thin sheet copper thickly covered with electrotype 

 copper. The results were generally somewhat irregular, but 

 they all showed a considerable loss of copper from the plate 

 to the solution*. 



The results of a series of weighings of plates of ordinary 

 copper sheet which were immersed in solutions of copper 

 sulphate of varying density and acidity for a period extending 

 in the aggregate to about seventy-one days are given in 



* Dr. Gore, in the paper above quoted, describes experiments on this 

 subject made by him both on the loss of copper in an acid solution of the 

 sulphate, and on the loss of the anode and cathode plates in a copper- 

 copper-sulphate electrolytic cell. Some of the results there given are in 

 agreement with the results of my experience as given below — for example, 

 the advisability of using high current-density for the measurement of 

 the electrochemical equivalent ; but the statement made to the effect that 

 a copper anode loses less by direct chemical action when the current is 

 flowing than when it is not, is not borne out by my experiments. 



