728 Proceedings of the Royal Society 
beaker, containing chloride of zinc solution, and a current passed 
through the cell from a bichromate battery, the zinc being deposited 
on the zinc plate. The chloride of zinc used was the commercial 
chloride, and this sample contained little or no lead and no copper. 
This cell was charged for about three hours, and then left stand- 
ing for twelve hours. At the end of that time I tested the ZnCl 2 
solution. It gave a brown coloration with H 2 S, but no precipitate. 
The zinc deposit was then dissolved in HC1, and some small black 
flakes were left insoluble in boiling dilute HC1. These flakes 
dissolved on adding a little chlorate of potash, and the solution 
thus prepared gave a blue coloration with ammonia, and a very 
small black precipitate with H 2 S. There was evidently, therefore, 
copper in the zinc deposit, but it was only a trace. Inside the 
parchment paper there was plenty of cuprous chloride, which was 
pure white, the parchment paper itself was green. I made several 
experiments of this kind ; sometimes I found more copper than at 
others. On these occasions the parchment paper was green, 
showing the presence of oxychloride, and therefore of cupric 
chloride. This was caused, I believe, by air bubbles under the 
parchment paper. Any copper found on the zinc plate is more 
likely to he due to this than to solution of the cuprous chloride. 
If it is at all soluble in chloride of zinc in the cold, it must be very 
slightly so. This loss from copper chloride diffusing cannot be 
more than 5 per cent, of the charge in forty-eight hours ; it is more 
likely in a properly made cell to be 1 per cent, or 2 per cent. It 
is difficult to settle its exact amount. 
With reference to the formation of oxychloride, I noticed one 
remarkable phenomenon which I cannot explain. If moist cuprous 
chloride is exposed to the air, oxychloride is formed ; but if the 
moist cuprous chloride is wrapped in parchment paper, and the 
outer surface of the parchment paper exposed to the air, the 
oxidation seems to go on through the parchment paper, and in a 
few hours the outer surface of the parchment paper is covered 
with a green slime of copper salts, that have in some way 
penetrated it. 
To test the working of this battery, I made up some primary 
cells with cuprous chloride and zinc plates. In these cells I 
foolishly used linen to wrap round the cuprous chloride paste, and 
