356 TENTH ANNUAL RErORT 0? 



of Grove's battery witli tliat of Daniell's. Sucli a comparison, how- 

 ever, can hold good only for an individual battery, since it changes with 

 the nature of the earthen cells, and is dependent upon the degree of 

 concentration of the liquid. 



A comparison of the resistance of these two batteries is of value only 

 when earthen cells of the same size are used for both, and the same 

 liquid for the zinc cells ; while the copper cell of Daniell's battery 

 should contain a concentrated solution of sulphate of copper, the 

 13latinum plate of Grove's should be in strong nitric acid. I have 

 not made such a comparison for the Grove's battery, but I have for the 

 zinc and carbon battery^ the resistance of which under otherwise like 

 circumstances may be considered equal to that of Grove's. Thus we 

 will return to the comparison of resistance in the zinc and carbon 

 battery. 



The proposition has been made to substitute for the nitric acid 

 another substance also containing much oxygen, namely : a solution 

 of bichromate of potash. With this liquid, Poggendorff found the 

 electro-motive force of Grove's battery equal to — 



0.987", 

 that of Daniell's battery being equal to 1 ; thus considerably less than 

 with nitric acid. Hence, bichromate of potash is not to be recom- 

 mended for Grove's battery. 



In the 106th volume of Dingler's Polytechnic Journal, P^'ge 154, 

 it is stated, that in using Grove's battery for telegraphic purposes, it 

 often happens that the nitric acid penetrates through the earthen cells, 

 and attacks the zinc so powerfully that it has to be newly amalgamated 

 every day. Crystals of Glauber salts cast into the dilute sulphuric 

 acid are said to remedy this evil. The explanation of this may probably 

 be that the Glauber salts are decomposed, and nitrate of soda is formed, 

 the free nitric acid then disappearing. 



§19. Bunsen's battery. — As a mean of all my experiments, stated 

 in section 9, the electro-motive force of the zinc and carbon battery 

 was found to have, in chemical measure, the value — 



824. 



The force of Daniell's battery being made equal to 1, that of the 

 zinc and carbon battery was found by 



Buff to be 1.712 



Poggendorff ; 1.548 



Expressed in chemical measure the force of the battery, according to 



Buff, is 805 



which accords nearly with my mean ; and according to 



Poggendorff is 727 



The electro-motive force of the zinc and carbon battery, and that of 

 Grove's, are so nearly equal, that in practical use the little difference 

 may be disregarded. 



According to Poggendorff, the electro-motive force of Bunsen's 

 battery remains almost the same, if for the nitric acid is substituted 

 a solution of bichromate of potash ; indeed, with the liquid it is some- 

 what greater, the proportion being 1,580 to 1,548. 



