THE SMITHSONIAN INSTITUTION. 393 



wliile the voltameter with platinized platinum plates, under the same 

 circumstances J yielded 



77. G8 cubic centimetres; 



thus nearly 87 times as much. 



This is due simply to the fact, that the polarization in platinized 

 plates is considerably less than in uncoated plates. Poggendorff has 

 proved this by direct measurements. 



The electro-motive force of a battery of two Grove's elements was 

 =. 64 ; after inserting the platinized plates it was 31 ; hence the po- 

 larization of the platinized plates was 



04—31 = 33. 



When, instead of the voltameter with platinized plates, that with 

 uncoated platinum plates was substituted, the electro-motive force of 

 the whole battery was eq[ual to 22 ; therefore the polarization on the 

 uncoated plate was 



64 — 22 = 42. 



It is shown, in section 18, that the electro-motive force of a Grove 

 element, as a mean of the observation of different physicists, is 777 

 in chemical measure ; hence the electro-motive force of two elements 

 equals 1554 ; therefore the value of the polarization of the uncoated 

 plates which Poggendorff found, reduced to chemical measure, is 



1554 

 42 X -g^=1020; 



which accords very closely with the value of the polarization given 

 above in section 32. 



Hence the polarization for platinized plates, in chemical measure, is 



1554 

 33 X -gj- = 801. 



Poggendorff also found, as mentioned already in section 34, that 

 the magnitude of the polarization diminishes with the strength of the 

 current ; when, by the increase of the accidental resistance, the cur- 

 rent was so weakened that the needle of the sine compass, inserted in 

 the closing arc, receded from 47° 49' to 5° 44', the polarization in the 

 voltameter diminished from 42 to 38, or, in chemical measure, from 

 1020 to 922. 



According to Poggendorff 's experiments, the magnitude of the po- 

 larization with platinized plates is but little dependent upon the 

 changes of the strengtli of the current, so that it may be considered 

 constant, without sensible error. 



Svanberg also has instituted many experiments in galvanic po- 

 larization, and with great care and accuracy, (Pogg. Ann., LXXIII, 

 298.) For the polarization v/hich the current of four Daniell ele- 

 ments produced in a voltameter with uncoated platinum plates, he 

 found, reduced to chemical measure, the value 



:•■ Svanberg observed;^ thiil the polarization in the voltameter increases 

 gradually, and requires some time to attain a maximum. Therefore, 

 to determine the maximum polarization accurately, he made his meas- 



