CRYSTALS OF COPPER ON ELECTRODES. 77 



gravity to the medal. There are, no doubt, a few slight objections 

 to placing the medal under the positive electrode such as the im- 

 parities in the copper getting disintegrated, and falling upon the 

 surface, but a piece of cloth wrapped round the pole prevents this. 

 However, when a fine surface is wanted, care ought always to be 

 taken to have clean solutions filtered, and kept covered from dust ; 

 and when the single-cell is used, the crystals of sulphate of copper 

 should be suspended in a fine linen bag, or the shelf holding them 

 be lined with linen. 



Effects of Difference in the Density of Solution. Although in prin- 

 ciple this is the best method, we believe that very few practise it, 

 because of the trouble attending the arrangement of the electrodes 

 in this position. When the medals are small the annoyances from 

 unequal density are not so material, but if the surface of the article 

 which is being deposited be large say eight inches or upwards the 

 difference in the thickness of the lower and upper portion of the 

 medal is very great. If it is not convenient to place them horizon- 

 tally, they should be shifted several times, making the upper portion 

 the lower, besides occasionally stirring the solution, or shaking the 

 article. Indeed, when convenient, the article receiving the deposit, 

 if suspended perpendicularly, should be kept as much in motion as 

 possible, as it regulates the deposit, making it smoother and less 

 brittle. 



Crystals of Copper on Electrodes. It will be found, when work- 

 ing with a battery, that the sulphate of copper solution will become 

 stronger round the positive electrode, which is gradually dissolved 

 by the transferred acid. A frequent effect is, that the electrode 

 often gets coated over with crystals of sulphate of copper, which 

 adhere with great tenacity, and stop the electric action. Under such 

 circumstances, it is only necessary to clean the electrode from the 

 crystals, and to add a little water to the solution, which will prevent 

 a recurrence of the crystals for a time. But the stirring of the solu- 

 tion occasionally will do much to prevent this crystallization. 





