392 TENTH ANNUAL REPORT OF 



Iron in sulphuric acid 2.92 



Tin in do do 2.95 



Copper in solution of potash 3.10 



Tin in solution of potash 3.94 



Zinc in dilute nitric acid 4.05 



Zinc in dilute hydrochloric acid 4.07 



Zinc in sulphuric acid 4.17 



Iron in solution of potash 4.65 



Zinc in do do 5.48 



For zinc in sulphuric acid, and copper in sulphate of copper, these 

 two Kussian physicists found the electro-motive force 2.17. This 

 gives us a point of reference for reducing the numerical values, given 

 above, for polarization and electro-motive force to our (the chemical) 

 unit. We have found for the electro-motive force of a Daniell ele- 

 ment the value of 470 (section 9) ; and to reduce the values given hj 

 Lenz and Saweljev to chemical measure they must be multiplied by 



^ = 217. 



For the electro-motive force of a Grove's element, (platinum in ni- 

 tric acid, zinc in sulphuric acid,) they found the electro-motive force 

 4.17 ; consequently, in chemical measure, it is 4.17 X 217 = 905. 



Hence, for the polarization of different metallic plates, we get the 

 following values expressed in chemical measure : 



Platinum in oxygen 538 



Platinum in hydrogen 651 



Zinc " " 217 



Copper " " 466 



Tin " '' 314 



Iron " " 72 



Carbon in oxygen 271 



for the entire polarization of the two platinum electrodes in dilute sul- 

 phuric acid 



1185, 



while for this case I found the number (seciSbn 32) 



1000. 



§36. Polarization in platinized ijlatimmi plates. — Poggendorff ob- 

 served, accidentally, that in an element of the Grove gas column, 

 which was inserted in the closing arc of a Grove element, a consider- 

 able development of gas took place unexpectedly, while a simple 

 Grove element, closed by a voltameter with uncoated platinum plates, 

 produced a very inconsiderable decomposition of water. (Pogg. Ann., 

 LXX 183.) 



For making comparative measurements, he constructed a voltameter 

 with platinized platinmn plates, which he compared with an ordinary 

 voltameter. The voltameter with uncoated plates yielded in the 

 closing arc of a Grove element, in thirty minutes, 



0.89 cubic centimetres of explosive gas ; 



