224 THE ELECTRIC TELEGRAPH. 



place faster during the time the circuit is open than when 

 it is closed. 



5. Kramer's Modification of Darnell's Battery. Kramer 

 has had these difficulties in view, and has succeeded partly 

 in overcoming them by interposing, between the zinc and 

 copper plates, two porous diaphragms, the space between 

 them being filled with diluted sulphuric acid, and containing 

 a copper plate of large surface in connection with the 

 ordinary copper plate of the element. 



The duties which the copper plate has to fulfil in the 

 ordinary form of Daniell's element are in this way divided, 

 the interposed copper plate acting, principally by reason of 

 its large surface and proximity to the zinc plate, in con- 

 ducting the current from the other elements when set up 

 with others in a battery j while the other copper plate, 

 immersed in the salt solution, fulfils mainly the functions 

 of a copper electro-motor for the element itself. 



The interior copper cup is first filled with crystals of 

 sulphate, and then all three compartments are filled up to 

 within an inch of the top with sulphuric acid diluted with 

 100 times its weight of water. The distance of the sulphate 

 of copper from the zinc plate being considerable, little or 

 none of the salt can reach it, and hence little or no loss 

 of materials can take place by diffusion. 



6. Meidinger's Modification of Daniell's Battery. Professor 

 Meidinger has introduced a still bolder modification of 

 Daniell's battery, in which the members are so differently 

 arranged as almost to claim the title of an original invention. 



Instead of separating the solutions of the sulphates by a 

 porous diaphragm to prevent their mechanical mixture, 

 Meidinger depends wholly for their separation upon the 

 difference of their specific gravities, by which the detrimental 

 precipitation of metallic copper upon the zinc pole is pre- 

 vented. A condition is, however, necessitated in the employ- 

 ment of Meidinger's element, which is not in that of any of 

 the others ; it is that, when once set up, the battery must 

 remain entirely undisturbed, otherwise the evil which it is 

 proposed to obviate is only increased. 



