46 Self-sustaining Voltaic Battery. 
screwed a thick copper wire, which projects out horizontally two 
inches and a quarter, and then drops three inches and an eighth. 
Into the end of this wire is tapped a piece of platinum wire, 
which is left projecting about an eighth of an inch. Every part 
of the copper-wire should be thoronghly coated with cement or 
encased with a glass tube, or the vertical part may be encased with 
glass and the horizontal with cement; but when glass is used, it 
should be cemented on so as to exclude entirely the liquid of the 
battery, thus preventing its contact with the copper. If cement 
alone is used, the wire should first be wrapped, otherwise the ce- 
ment is liable to become detached, as it does not hold so well to 
the copper as it does to the wrappin 
The zinc plates of the battery should be one-fourth of an inch 
thick, and of the length of the inside of the jar or tray. The zinc 
should be well amalgamated, and then placed in the jar with the 
edge resting in the tray, and the tray filled with mercury. The 
plate is secured in place by its length and by the encased wire 
from the adjacent cell, which hinders it from falling forward. 
But the terminal zinc must be secured by a wire similarly en- 
cased and tipped with platinum to dip into its mercury tray, an 
then bent down against the outside of the jar to a glass or iron 
cup containing mercury, for continuing the circuit, 
The wire from the terminal silver should. dip into a similar 
cup. If, then, the conductor which continues the circuit be en- 
cased and tipped with platinum, the current may be led off from 
any portion of the train by inserting the conductor into the mer- 
cur y- . 
The | jars are charged with a sat of one part of sulphuric 
acid, and six parts of water. ‘These proportions are calculated — 
for dissolving all the zine and all the ae formed, and leav- 
ing a slight excess of acid and water. 
When the mixture of acid and water is made, it should be 
oe i to get cold before it is put into the jars, if the silvers are 
o be put in; for a hot solution of sulphuric acid would act on 
ne silver, and dissolve a portion, which, though very small, 
would ruin = ns silver and the zine plates, as will presently 
be made to 
Lastly, ae piven plates should never be put into the acid 
when the zines are not in, as in that case the silver, not being . 
enfilmed by hydrogen, would be in danger from the acid: 
To hinder evaporation from the jars, the battery is placed in & 
box made with a double rim on the lid so as to form a deep 
trough or recess, into which the walls of the box go when the 
lid is put on, When the battery is to remain a long time with 
out attention, the box should be completely air-tight. 
I have devised no special plan for hindering the mat 
for the particular circumstances in which the battery is placed 
