202 
THE TELEGRAPH, 
zinc attached to it, the lower one the copper. Each terminates 
externally in a binding screw, and an India-rubber washer is 
used to make the joint tight. A glass cup is supported by the 
zinc, and its tube reaches down to the level of the copper 
plate. 
Water, or water containing a little sulphate of zinc, common 
salt, or sulphuric acid, is poured into the vessel, while the cup 
is filled with a solution of copper sulphate. This very heavy 
solution falls to the bottom of the vessel, and, without mixing 
with the other liquid, raises up the latter until it reaches the zinc. 
“ The electric current is produced immediately. Crystals of 
copper sulphate are thrown into the cup, and there keep the 
solution saturated, in spite of the working of the battery.” 
“ This battery is easily used, and has the advantage of being 
covered up. In it the inconveniences caused by porous vessels, 
which have already been mentioned in speaking of the Daniell 
cells, are completely avoided. The French government and 
railway telegraphs make use of great numbers of cells enclosed 
in boxes ; the Callaud cells arranged for this purpose are very 
simple. They are shown in fig. 140. 
“ These cells are charged in the same way ; but as they have 
no glass cup, a siphon or funnel is used in adding the solution 
of copper sulphate. Another arrangement is to hang the 
zinc to the edge of a plain vessel. Tne Callaud cells lessen 
the costs of maintaining telegraph batteries by 60 per cent. ; a 
circumstance proved by the reports that telegraph inspectors 
have given to their directors in cases where this plan is 
adopted. We have here, depend upon it, a solution of the 
problem of cheap electricity; at least, this is one of the most 
economical sources of electricity. 
“ The experience of twenty-five years has confirmed its 
advantages. It is used by telegraph companies in France, 
Spain, Italy, Germany and England. In the United States of 
America great numbers of these cells are used.” 
Cells with two liquids of different densities have been con¬ 
trived in other countries as well as in France ; and we have 
already seen that Sir W. Thomson’s cell much resembles that 
of Callaud. Meidinger’s cell (fig. 140) is used in Germany, 
and its shape is like a battery that has long been used in 
France. 
