THE TELEGRAPH. 
liquids to drop out into another vessel; so the liquid within 
the cell is gradually drawn out from about the middle of its 
height. In this way the greater part of the sulphate of copper 
as it rises through the liquid by diffusion, is drawn off by the 
siphon before it can reach the zinc, which is thus left 
surrounded by a liquid that is almost entirely free from any 
admixture with sulphate of copper, and having a very slow 
downward motion counteracting the upward movement of the 
sulphate of copper. When the battery is in action, copper is 
Fig. 131. 
deposited on the lower plate, and the. sulphuric * cid slowly 
traverses the liquid until it reaches the zinc, with which it com¬ 
bines to form sulphate of zinc. In order that the specific gravi¬ 
ties of the solutions should be maintained in due relation to each 
other, it is necessary to keep the central tube well filled with 
crystals of copper sulphate, and to fill up the cell with a solu¬ 
tion of sulphate of zinc sufficiently dilute to make it the lightest 
stratum of liquid. *. 
Daniell’s is not the most powerful of the batteries in use. 
Grove’s and Bunsen’s have nearly double the electro-motive 
force ; but the chief merit of Daniell’s combination is the 
constancy it possesses, more particularly in the practical forms 
that Minotto and Siemens have given to it. . 
The internal resistance of a Daniell’s cell is generally 
greater than that of a Grove’s or a Bunsen’s cell of the same 
