92 Dr. Beetz on the Electromotive Force of Gases. 



charge is diminished, we ought to find, on applying the com- 

 pensating method, that a circuit with platinized plates ex- 

 hibited no more power than one with polished plates, provided 

 the platinum had been purified sufficiendy. I therefore con- 

 structed gas batteries of polished plates of platinum, which 

 had been boiled in concentrated nitric acid and then in water. 

 These batteries yielded the following results : — 



' fFhis agreement was to have been anticipated from the ex- 

 periments which Faraday* made upon the condensing action 

 of pure platinum upon gases; and Poggendorfff has already 

 rendered it probable, that the primary forces of gas batteries 

 with polished, gray, or black platinized plates, would be the 

 same in each case. But at the same time the agreement of 

 these observations yields a proof, that with the extremely short 

 closure of the circuit, which the compensating method requires, 

 the polarization does not attain any important value; other- 

 wise the polished plates, which are capable of being more 

 powerfully charged, would give smaller values. 



I finally passed to experiments with gas batteries, the solid 

 conductor of which consisted of some other body than pla- 

 tinum. I then met with a great difficulty in the small values 

 of the electromotive forces, which in most cases rendered a 

 determination of the relation existing between them almost 

 impossible. Even on using Bunsen's coke batteries, from 

 which Poggendorff J anticipated great action, the forces were 

 not very great, and moreover still variable. It was only with 

 very great difficulty that I could cut discs of the coke, even 

 from the same piece, which were tolerably uniform. This is of 

 more consequence, because after what has been stated above, 

 we have no means of rendering them uniform artificially. The 

 pieces of coke were boiled for several hours with nitric acid, 

 then with water, afterwards with dilute sulphuric acid, and 

 again with water; yet I very frequently found that when the 

 tubes were filled with any inodorous gas in which these pieces 



* Experimental Researches, § 670, 605. J Loc. cit. 



f Poggendorflf's Annalen, vol. Ixi. p. 598. 



