THE SMITHSONIAN INSTITUTION. 357 



According to the statements made in section 9, witli like mean 

 surfaces, similar clay cells and equally dilute sulphuric acid, the re- 

 sistance to conduction of the zinc and carbon battery is to that of 

 Daniell's, as — 



43 to 78 ; 

 or as — 



1 to 1.8. 



Stohrer, of Leipsic, has recently considerably improved the Bunsen 

 battery, and made it more convenient for use. His carbon cylinders are 

 steeped in coal-tar instead of sugar-water, and are then brought to 

 a red heat. They are far more solid and have a much smoother surface, 

 which gives them the advantage of absorbing much less nitric acid, 

 which before rendered the use of this battery particularly unpleasant 

 and expensive. 



In the first zinc and carbon batteries the copper or zinc ring, which 

 embraced the upper edge of the carbon cylinder, was generally mova- 

 ble. Stohrer has rendered this fixed. A strip of brass wire is wound 

 about the edge of the carbon cylinder, and a copper ring is screwed 

 in this as firmly as possible. The whole of the upper part is then 

 coated with a solution of shellac. A wire, about one inch long, 

 is fixed to the copper ring, serving as a connexion with the next 

 zinc cylinder. A kind of wire cord, coated with gutta percha, is fast- 

 ened to the zinc cylinder, and terminates in a binding screw, which 

 can be attached to the copper wire of the following carbon cylinder. 



§ 20. Zinc and iron hattery. — It has been proposed by many to 

 use iron instead of platinum or copper in the construction of gal- 

 vanic batteries. Eoberts made a zinc and iron battery in the follow- 

 ing manner. A cast-iron vessel, ten inches high and 3.9 inches in 

 diameter, served for holding a mixture of one part concentrated sul- 

 phuric acid and three parts of strong nitric acid ; in this liquid an 

 earthen cell filled with dilute sulphuric acid was placed, which cell 

 also served for the reception of the zinc cylinder 9.9 inches high and 

 3.3 inches wide. 



Five such elements yielded forty cubic inches of detonating gas in 

 a voltametre placed in the circuit. This is certainly quite a consid- 

 erable effect. (Dingler's Journal, vol. 84, p. 386.) 



^ In the same volume of this Journal, p. 385, Schonbein describes a 

 zinc and iron battery which also produced very considerable effects. 



Roberts proposed a battery of this kind, with one liquid, for blast- 

 ing rock. (Dingler's Journal, vol. 87, p. 104; Mechanics' Magazine, 

 1842.) 20 iron plates and 20 zinc plates, each having 7 square inches 

 of surface, are properly connected and so placed in a frame of slats, that 

 they may be immersed in a trough containing a mixture of 1 part sul- 

 phuric acid to 10 parts water. 



