APPENDIX. 441 



impediments to conduction. The above is Ohm's law. By 

 the electro-motive force, is to be understood the whole force 

 generated by the chemical action in the battery. The im- 

 pediments are found in the imperfect conducting power of 

 the bodies, whether liquid or solid, which enter into the cir- 

 cuit, and the resistance which the current encounters in 

 passing from one to another. 



273. (1.) 



SMEE'S BATTERY. Of all the batteries in common use, 

 Smee's, which is represented in the figure, 

 is the simplest. It consists of a plate of 

 silver, with plates of zinc hanging near it 

 on either side. The two zinc plates com- 

 municate with each other by a metallic 

 connection, and are, therefore, but one 

 plate. It is found best to roughen the 

 silver with platinum black. Smees' bat-j 

 teries are commonly sold in this condition. 

 The clamp and bar are simply to keep the 

 plates in place. Water acidulated with 

 from one-seventh to one-sixteenth of its bulk of oil of vitriol, 

 is employed in this battery. It is generally used in plating, 

 and is recommended to the student on account of its cheap- 

 ness, simplicity, and efficiency. 



273. (2.) 



GROVES' BATTERY. In Groves' battery the metal plati- 

 num is used, instead of copper or silver. It is placed by 

 itself, in a porous earthern cup containing nitric acid. The 

 vessel is placed in a larger one, containing zinc and sulphuric 

 acid. The two acids mix to some extent through the pores 

 of the inner cup, so as to complete the circuit by their con- 

 19* 



