chap, li.] SMEE'S ELEMENT. 21 



grating to keep up the level of the fluid, and to main- 

 tain the dilution of the upper stratum. 



In Mice's element the metals are zinc and 

 platinum, or platinised silver. Two plates of zinc are 

 clamped on a wooden frame, and the platinum, which 

 is roughened by being covered with a deposit of finely 

 divided platinum, is fixed between them, being kept 

 from touching by the frame. Thus both sides of the 



o < 



platinum are used. Dilute sulphuric acid is the liquid. 

 The action is the same as that described in the voltaic 

 element, only the platinum presents a surface from 

 which the hydrogen bubbles can be more readily dis- 

 engaged, and so polarisation is mechanically prevented. 



The platinum is + pole, and zinc . 



Orove's element has two metals and two fluids. 

 The containing vessel may be of glass or earthenware 

 or ebonite. It contains dilute sulphuric acid, and 

 a cylinder of zinc. An inner compartment, formed 

 by a porous cell placed inside the zinc roll, contains 

 strong nitric acid and a platinum plate. (See Eig. 10, 

 Bunseii's element, the construction of which is similar.) 

 The sulphuric acid attacks the zinc, forms zinc sul- 

 phate, and liberates hydrogen, which passes to the 

 inner compartment, and forms water at the expense 

 of the nitric acid, which is reduced to nitrous acid. 



Thus, 



H 2 S0 4 + Zn == ZnS0 4 + H 2 (1) . 

 H 2 + HX0 3 = HXOo + H,6 (2). 



Grove's element gives great power, but the strong 

 acids make it unpleasant to handle, and the nitrous 

 fumes given off are extremely disagreeable and irrita- 

 ting, and besides are very injurious to instruments. 

 The cells should, therefore, be kept in a room or shed 

 apart from where persons are working. 



Platinum is -f- pole, zinc . 



