PART II. GENERATORS OF ELECTRIC 

 LIGHT. 



WE have seen that the electric generators which can be 

 advantageously used for the electric light are batteries with 

 acids, particularly Bunsen's battery, thermo-electric piles, 

 and magneto-electric induction machines. Which arrange- 

 ments of these generators are the best? This is what we 

 are about to study in the present chapter. 



VOLTAIC GENERATORS. 



In the battery invented by Grove in 1839, two liquids are 

 made use of: nitric acid on the one hand, and water acidu- 

 lated with sulphuric acid on the other; and in order to place 

 these two liquids in contact without mixing them, the one is 

 poured into a vessel of half-baked porcelain, generally called 

 a porous vessel, which is plunged into another vessel of glass 

 or glazed stoneware. Vessels of earthenware or of crockery- 

 ware are of no use, on account of damage they receive from 

 the action of acids, and from the crystallization of sulphate 

 of zinc which forms inside of the pores of those substances. 



The nitric acid is generally placed in the porous vessel, 

 and water, acidulated to a tenth of its weight, in the glass 

 vessel ; then the positive electrode which gives the negative 

 pole is formed by a plate of amalgamated zinc rolled into 

 a cylinder, within which is placed the porous vessel. The 

 negative electrode is formed of a prism of retort carbon, cut 



