726 
Proceedings of the Royal Society 
I have found paper pulp very useful in batteries which have 
to be carried about. It is capable of holding 80 per cent, of 
its weight of water, when not squeezed. It is soluble in strong 
iodide of zinc, forming a transparent jelly, and turns black in the 
iodine solution, as does the parchment paper. Iodide of zinc, if 
exposed to the air in presence of paper pulp, sets free iodine. 
From the above summary of my attempts, it is evidently 
hopeless to expect a practical secondary cell, in which the active 
agent is in solution. I accordingly tried to find some method for 
storing the iodine on the carbon plate in an insoluble form. It is 
unnecessary here to mention the various substances I covered the 
carbon plate with, in the hope that the iodine would form with 
them an insoluble compound easily decomposable. The only sub- 
stance among those which I tried that worked at all was starch. 
This took up a certain amount of iodine when spread over the 
carbon plate in a thick paste, and the cell when thus charged gave 
a current. These experiments were, however, brought to a conclusion 
by my devising the cell which I now propose to describe in the 
remainder of this paper. 
Cuprous Chloride Cell . — In this cell chloride of zinc is used, both 
because of its cheapness and of the higher electromotive force it 
gives. Iodide of zinc may also be used. The uncharged cell con- 
sists of two copper plates immersed in a solution of chloride of zinc. 
By passing an electric current through it, the chloride of zinc is 
decomposed, zinc being deposited on the one copper plate and 
chlorine being separated at the other copper plate. The chlorine 
never appears in the free state ; it combines with the copper to form 
cuprous chloride, an insoluble white precipitate. The cuprous 
chloride is held against the copper plate by a sheet of parchment 
paper. This cell is now charged, and will supply a current until all 
the zinc is reconverted into chloride of zinc, and the cuprous chloride 
is reduced to metallic copper. The action of the cell is quite simple. 
As soon as the circuit is completed, the usual electrolytic state is set 
up. The chlorine of the chloride of zinc nearest the zinc deposit 
combines with the zinc, and the zinc separated at the other plate 
combines with the chlorine of the cuprous chloride to form chloride 
of zinc. It is a case of action at a distance, as in Grove’s gas battery. 
