SOURCES OF ELECTRICITY. 197 
dimensions. This defect is compensated by the length of time 
the cell will continue to work well, and by its emitting no 
noxious fumes or gases. 
The Siemens-Halske battery is a modification of DanieH’s, 
differing from the latter chiefly in the shape of the porous 
vessel. A (fig. 133) is the glass or glazed earthenware vessel 
used in all batteries, c is the diaphragm, a porous vessel 
which, instead of being simply cylindrical, widens out at the 
base where it stands on the bottom of A. It is open at both 
ends, k is the plate of copper, which in this case is bent into 
Fig. 132. 
the shape of two intersecting s’s. c is filled with sulphate of 
zinc and water ; g is a mass of papier-mache in pulp, heaped 
up above the base of the porous vessel. ■ z is a ring of zinc 
surrounding the porous vessel and provided with a screw. 
The whole is filled with a saline solution, or with acidulated 
water, up to about half the height of the zinc. Afterward it is 
necessary only to keep the vessel c filled with crystals of 
sulphate of copper, and replace the water in the outside vessel 
from time to time. The sulphuric acid required for the 
formation of the sulphate of zinc is carried by the current itself 
through the diaphragm. The zinc need not be amalgamated. 
