THE SMITHSONIAN INSTITUTION. 355 



Danlell's battery is, perhaps, the most constant of all, which is due 

 partly to the acid being used up less rapidly ; since the acid, set free 

 by the decomposition of the sulphate of copper, passes in part at least 

 through tlie porous cell to the liquid in which the zinc is immersed. 



Ryhiner (Dingler's Journal, vol. 110, p. 418) proposes to substitute 

 iron for zinc, and to place it in a solution of common salt. The ad- 

 vantage of this combination is not clearly seen. Its electro-motive 

 force is certainly less than that of the ordinary Daniell's battery. 



Eyhincr says of his battery : Though it has not a strong influence 

 on the magnetic needle, it has, nevertheless, a greater reducing effect 

 on metallic solutions than the ordinary zinc battery ! (?) 



Mr. Ryhiner appears not to know that the chemical effect of a cur- 

 rent is always proportional to its magnetic effect. 



Moreover, he proposes to substitute linen cells for clay cells, 

 which is quite practicable. One is often in fact embarrassed to get 

 clay cells. Those made by the potter are bad ; good ones cannot be 

 had everywhere ; and this is the more annoying because the best cells 

 are the most fragile, flyhiner's cells are made in the following way : 



A bag, without ends, is formed of stout twilled linen cloth, and 

 stretched over a tin cylinder ; on this, three or four plies of stout 

 paper are fastened with Hour paste, and the whole covered with a 

 piece of thin linen. The bottom is made of a flat wooden cylinder, 

 with a groove on its edge, to which the linen is tied fast with twine. 

 The tin cylinder is replaced and filled with hot sand. When all is 

 thoroughly dried, melted wax or rosin is poured in, to stop the cracks 

 in the bottom. The upper edge is soaked in amber varnish. 



Whether these cells are really to be recommended, I am unable to 

 decide from my own experience. 



§ 18. Grove's hatterij. — According to my measurements, given in 

 section 9 — which, however, for Grove's battery, have no claim to 

 great accuracy — the electro-motive force of this battery is, in chemical 

 measures, 829. 



Other observers have determined its force, not in an absolute meas- 

 ure, but compared with that of Daniell's battery. Making the elec- 

 tro-motive force of the latter equal to 1, we have for Grove's as fol- 

 lows : 



By Jacobi 1.666 



By Buff. 1.712 



By Poggendorff , 1.668 



By do 1.565 



Mean ...., 1.653 



Assuming the force of Daniell's battery in chemical measure, ac- 

 cording to my determination, equal to 470, we should have, in the 

 same measure, that of Grove's equal to 



470 X 1.653= 777; 

 while I found the value of the electro-motive force of this battery to be 

 829, or about 6| per cent, greater. 

 The observers above named made no comparison of the resistance 



