142 



ELEMENTARY LESSONS ON [CHAP. in. 



surface of the carbon and the copper strap which 

 connects the carbon of one cell to the zinc of the next. 

 Fig. 75 shows the usual way of 

 coupling up a series of five such 

 cells. The Bunsen's battery will 

 continue to furnish a current for 

 a longer time than the flat 

 Grove's cells, on account of the 

 larger quantity of acid contained 

 by the cylindrical pots. 1 



173. Leclanch^'s Battery: 

 Niaudet's Battery. For work- 

 ing electric bells and telephones, 

 an( l a l so to a limited extent in 

 telegraphy, a zinc-carbon cell is 

 employed, invented by Mons. 

 Leclanche', in which the exciting liquid is not dilute 

 acid, but a solution of salammoniac. In this the zinc 

 dissolves, forming a double chloride of zinc and am- 

 monia, while ammonia gas and hydrogen are liberated 



j 



at the carbon pole. To prevent polarisation the carbon 

 plate is packed inside a porous pot along with frag- 



1 Callan constructed a large battery in which cast-iron formed the positive 

 pole, being immersed in strong nitric acid, the zincs dipping into dilute acid. 

 The iron under these circumstances is not acted upon by the acid, but 

 assumes a so-called "passive state." In this condition its surface appears 

 to be impregnated with a film of magnetic peroxide, or of oxygen 



