

SCIENCE AND PRACTICE. 



225 



Fig. 118. 



Meidinger's element is set up in a cylindrical glass jar, 

 A A, Fig. 118, on the bottom of which is cemented a glass 

 cup, d d. The diameter of the outer vessel is larger above 

 than below, being provided, at about a third of its height 

 from the bottom, with a shoulder, b b. 

 A cylinder, z z, of amalgamated zinc, 

 sits upon this shoulder, and is of such _ 

 dimensions as to fit comfortably into x! 

 the upper part of the vessel. The 

 interior of the cup d d is covered 

 similarly with a cylinder, e, of copper, 

 to which a copper wire, g, insulated 

 with gutta-percha, is attached, and 

 leads out of the element. The 

 glass vessel A A is covered by a wooden 

 disc, provided with a hole for the wire 

 g to pass through, and one also for a 

 glass tube, h, formed like a test- 

 tube, pierced at the bottom with a few small holes. The glass 

 .tube h is fixed in the centre of the wooden cover, and 

 reaches to about half-way down inside the cup e. 



The element is charged by filling it to the top of the zinc 

 cylinder with Epsom salts solution, and the tube h with 

 crystals of sulphate of copper. The sulphate of copper 

 dissolving, saturates the water containing Epsom salts, and 

 the solution being specifically heavier, descends through 

 the hole at the bottom of the tube into the cup d d, which 

 it about half fills. 



So long as the element remains unshaken, the fluids retain 

 their respective places, and the diffusion of the sulphate of 

 copper into the solution of sulphates of zinc and magnesia 

 above takes place so slowly that, after a battery has stood 

 a month or two, scarcely a trace of copper is to be observed 

 on the zinc ring. Further, a great advantage is offered by 

 the circular space between the cup d d and the sides of the 

 vessel A A, into which the particles of iron and other foreign 

 metals, divided from zinc, fall without coming into contact 

 with the sulphate of copper. 



