THE SMITHSONIAN INSTITUTION. 391 



sum of the polarization of both plates ; the polarization of platinum 

 by oxygen being 2.48 ; that of the same metal by hydrogen is 

 5.46 — 2.48 = 2.98, or nearly 3. 



In the four succeeding cases, (zinc, copper, tin, and iron, in sul- 

 phuric acid,) the positive electrode is attacked, and therefore the cor- 

 responding numerical values are those of the polarization of these 

 metals by hydrogen. Arranging these results, we have for the po- 

 larization of 



Platinum in oxygen 2.48 



Platinum in hydrogen 3.00 



Zinc in do 1.00 



Copper in do 2.15 



Tin in do 1.45 



Iron in do 0.33 



Graphite or carbon in oxygen 1.25 



If we introduce into the closing circuit of a battery a decomposing 

 cell of unlike plates, this itself will act as an electro-motor, and the effect 

 of its force will, according to circumstances, either favor or oppose 

 the polarization. Suppose the electro-motive force of the decomposing 

 cell, as well as its polarization, to oppose the electro-motive force of 

 the battery, then the difference D obtained from the measurements of 

 the electro-motive force of the battery, with and without the decom- 

 posing cell in the circuit, will be the sum of the electro-motive force 

 of the decomposing cell, and of the polarization, or 



denoting by e the electro-motive force of the decomposing cell, and by 

 p the polarization taking place in it. If we have determined the 

 value of D for difierently constructed decomposing cells, (say, for, ex- 

 ample, consisting of platinum in nitric acid, and zinc in sulphuric 

 acid, platinum in nitric acid, and copper in a potash solution,) we 

 can compute for these combinations the value of e by deducting the 

 respective values of p. In this manner Lenz and Saweljev ascertained 

 the electro-motive force of the following combinations : 

 FlxLiinuin in nitric acid, combined with — 



Platinum in hydrochloric acid 0.26 



Do sulphuric acid 0.02 



Do nitric acid 0.00 



Graphite in nitric acid 0.01 



Gold in nitric acid 0.06 



Gold in sulphuric acid 0.25 



Mercury in sulphuric acid O.TO 



Mercury in nitrate of mercury 0. 79 



Platinum in solution of potash..... 1.20 



Pure copper in sulphuric acid 1.39 



Slightly oxidized copper in sulphuric acid 1.75 



Copper in sulphate of copper 2.00 



Gold in solution of j^otash 2.31 



Tin in hydrochloric acid 2.38 



Iron in do ,...do 2.75 



Graphite in solution of potash 2.84 



