226 THE ELECTRIC TELEGRAPH. 



The chemical action being identically the same as that 

 of a common Daniell's element, the electro-motive force is 

 necessarily the same. The resistance of the element is, how- 

 ever, a little greater, resulting from the inferior conducting 

 power of the solution of Epsom salts, and the distance which 

 the plates are apart ; but even for local batteries this resist- 

 ance does not interfere materially with its applicability to 

 telegraphic purposes. 



7. Siemens and Halske's modification of Darnell's Battery. 

 MM. Siemens and Halske of Berlin have set themselves the 

 same task .-as Meidinger and others, and have produced the 

 battery which bears their names, the constancy of which 

 has been tried for some years, and found to answer their 

 expectations. 



These inventors directed their attention particularly to 

 the improvement of the diaphragm, 

 and sought for some substance which 

 would prevent the mixing of the 

 solutions and the unnecessary con- 

 sumption of zinc and sulphate of 

 copper. The substance recommended 

 by them is paper-pulp. An element 

 constructed with this material for 

 a diaphragm is shown in section in 

 Fig. 119. 



A A is a glass jar, at the bottom 

 Fig. 119. p , . , . & , , J , 



01 which is placed a cross of sheet 



copper, K, attached to a copper wire,/+, and over this a 

 tube, c c y of unglazed porcelain, the lower part of which is 

 widened out bell-fashion at c c. Between the porous bell 

 and the glass vessel, the paper-pulp is put to the height e, 

 well stamped down. 



The papier-mach6 as obtained from the paper-mills is 

 prepared first by being well pressed, then treated with a 

 quarter of its weight of English sulphuric acid, which is 

 worked together with it until the whole acquires a homo- 

 geneous glutinous structure ; after which four times as much 

 water is worked up with it for a few minutes, and, lastly, 

 the superfluous water is squeezed out by a press. 



