of Edinburgh, Session 1881-82. 
727 
What is curious about it, to my mind, is that an insoluble non-con- 
ductor should enter so readily into the action of the cell. It must 
be remembered that the zinc is never separated ; it takes up the 
chlorine from the cuprous chloride without ever appearing as zinc. 
It is impossible that it should appear as zinc, and it is therefore 
curious that it should ever reduce the cuprous chloride. The 
reduction of the cuprous chloride proceeds from the copper plate 
outwards. This question of what insoluble substances will enter 
into the action of a battery, and why they do so, is one of great 
importance, if primary batteries are ever to be cheap sources of 
electricity. 
This cell may also be used as a primary battery, one pole being 
a zinc plate and the other a copper plate surrounded by cuprous 
chloride. It has this great advantage as a primary battery, there 
is no waste from diffusion of one liquid into another, as in the 
Daniell cell. It is a one-fluid battery. With this advantage it has 
also the advantage of the Daniell cell, in being free from polarization, 
and in no gas being given off during its working. 
I measured its electromotive force on a Thomson electrometer, 
using a Daniell cell as my standard. Calling the electromotive 
force of a Daniell one volt, the electromotive force of my cell is 
*75 volt. To return to the secondary cells. The first point I 
proceeded to investigate, was whether the cell lost its charge on 
standing. This would only take place in a properly constructed 
cell by the solution of the cuprous chloride in the chloride of zinc, 
and its diffusion to the zinc plate, where it would be reduced to 
metallic copper, chloride of zinc being formed, or by some local action 
at the zinc deposit, between it and the copper plate. This local 
action does exist to a very slight extent, the water itself or traces 
of other salts than chloride of zinc being the cause. Chloride of 
zinc itself cannot, of course, produce local action between zinc and 
copper. The other form of loss, namely, from the solution of the 
cuprous chloride, I investigated as follows : — I made up a small 
cell, by taking a copper and a zinc plate of about 4 square inches 
surface, with wires soldered to them, wrapping the copper plate in 
parchment paper, and tying it and the zinc plate together with 
thread, two slips of wood, about a \ inch thick, being put between 
them to keep them, apart. This was then slipped into a small 
