PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 927 



gas Avhich accumulates upon the negative plate, causes it gradually 

 to subside. I have seen the galvanometer needle fall back three 

 or four degrees in the course of twenty minutes under the action 

 of a cup of this battery. This difficulty, and its want of intensity, 

 renders it unsatisfactory in telegraphing ; but it gives great quan- 

 tity, and in its electrolytic effects in throwing down metals and 

 other chemical uses, it is of great value. " 



Grovels hatterrj is too well known to require description. The 

 theory of its chemical action is such as to make it more powerful 

 for a given number of cups, in the combined properties of quantity^ 

 intensity and volume of intensity, than any other battery. But' 

 the enormous expense attending its use, together with the deleteri- 

 ous and corrosive fumes of nitrous acid, and nitric acid vapor, con- 

 tinually emanating from it, are highly objectionable. These 

 difficulties are largely in consequence of local action. If we put a 

 globule of mercury, or a piece of zinc, or of amalgamated zinc into 

 a tumbler, and pour upon it a little diluted nitric acid, a violent 

 effervescence takes place ; the tumbler soon becomes too hot to 

 be held by the naked hand, and the air is suffocatingly charged 

 with nitrous acid fumes. This is precisely what takes place in 

 every cup of Grove's battery, just in proportion to the quantity of 

 nitric acid, which, ])y its tendency to diffusion, percolates through 

 the porous cup ; and this, I think, may account for the remarkable 

 fact that this battery runs down nearly as fast when it works but 

 one line as when it charges several lines. Showinij that the con- 

 sumption of material is due more to this local action than to that 

 which generates the current. 



The foregoing objections have caused this battery to go out of 

 use in many j^laces, and to give place to the 



Chromic acid battery, which consists of the jar, the porous cup, 

 the amalgamated zink, and the carbon of Bunscn's battery, and 

 which, instead of nitric acid in the porous cup, is charged with 

 Poggendorff's solution, which, according to De la Rive (vol. 2, 

 p. 810), is composed of water, saturated with bichromate of pot- 

 ash and an equivalent of sulphuric acid. This liquid is so corro- 

 sive and oxydizing that it has been found almost impossible to 

 make connections with the carbons that would serve any length 

 of time, but A. S. Ogden, of Newark, N. J., and C. T, and J. N. 

 Chester of N. Y., have lately contrived modes of connection which 

 appear to be durable and safe. This liquid has the effect to satu- 

 rate or fill up the carbons with sesqui oxide of chromium^ which 



