80 ELEMENTS OF LABORATORY WORK 



In the Grove cell we have the zinc plate immersed in 

 dilute hydrogen sulphate, in which is also placed a porous 

 vessel containing strong hydrogen nitrate, and a sheet of 

 platinum. 



The Bunsen cell resembles the Grove, except that the sheet 

 of platinum is replaced by a plate of carbon. 



The Leclanche cell consists essentially of a carbon plate 

 and a zinc rod immersed in a solution of ammonium chloride. 

 The carbon plate, however, is packed with manganese dioxide 

 and carbon fragments in a porous vessel. 



The Bichromate cell consists of carbon and zinc plates 

 immersed in a mixture of potassium bichromate and hydrogen 

 sulphate, or in hydrogen chromate solution. 



54. Processes by which Electric Equilibrium is effected. 

 If two conducting bodies, mutually electrified either by friction, 

 induction, conduction, or by communication with a cell, are 

 insulated, and placed close together, they may be caused 

 to resume their normal condition by means of a small insulated 

 conductor (a gilt pith ball for instance) suspended by a silk 

 thread between them. This conductor will move to and fro 

 between them with considerable velocity, making repeated 

 contacts with each, which gradually diminish and cease. At 

 this point the two bodies will be found to be no longer elec- 

 trified, for with electroscopes and electrometers no indications 

 of that condition are given. 



These bodies may also be caused to resume their normal con- 

 dition by placing a metal between them by means of an insulat- 

 ing handle. The change in this case takes place with extreme 

 rapidity. It is effected by a momentary contact. At the 

 same time the process is not visible. The change takes place 

 without any displacement of matter. Any number of bodies, 

 put in electric connection with one another by means of 

 metals, immediately assume the same electric condition, what- 

 ever their original condition may have been. 



If a piece of very thin wire is placed in connection with 

 the two bodies, equilibrium is not reached so rapidly, and 

 may take a measurable time. During the process which brings 

 about equilibrium, the wire may be shown to be in a condition 



