82 Dr. Beetz on the Electromotive Force of Gases. 



electrolysis are for the most part again removed, and thus after 

 some time great constancy obtains. 



The object of the following investigations is therefore to 

 determine the electromotive force of the gas-battery quite in- 

 dependently of, or as much so as possible, the disturbing in- 

 fluence which prolonged closure of the current must exert. 

 For this purpose, the method of compensation proposed by 

 PoggendorfF* naturally presented itself; in the application of 

 which, the resistance of the circuit, the measurement of which 

 is desired, is entirely unknown, and the circuit requires to be 

 closed for a moment only. If three conductors, the resistances 

 of which are r, r' and r , meet in two points, r being a circuit 

 the electromotive force of which is k', and r' one the force of 

 which is k"i the. total intensity J" existing in r" will be equal 

 to the intensity which /«." would produce alone, jninus that 

 which // would have produced by its own action ; hence 



k" k' r 



J" = 



rr' , rr" r + r"' 



r"+——r r' + 



r + r' r + r" 



When J"=o, we have 



o=F(r+r')— A/r 



r+r 



Hence when the magnitude k' is given, k" is also known by. 

 the measurement of r and r'. The resistances were measured 

 by a rheochord spun over with German silver wire, in the 

 same manner as that adopted by PoggendorfF; r is represented 

 directly by a length of wire b ; r' consists of a length of wire 

 a, the resistance of the circuit k' (a Grove's platino-zinc cir- 

 cuit), = w, and the resistance of a galvanometer, with a simple 

 needle and but few coils, inserted in this closing wire, =g. 

 Lastly, the resistance r" consists of that of the circuit mea- 

 sured, and that of a delicate galvanometer G provided with 

 an astatic arrangement, with its conducting wires. Let the 

 resistances w-i-g be =R. After the positive plate of the cir- 

 cuit under measurement {ex. gr, that platinum plate which is 

 coated with hydrogen) had been connected by the wire b with 

 the platinum plate of the Grove's circuit, by the wire a and 

 the galvanometer g with the zinc plate of the latter, a wire 

 from the negative plate of the circuit under measurement 

 (platinum coated with oxygen) was connected with a delicate 

 galvanometer. Moreover, a wire from the platinum plate of 



* PoggendorlTs Annalen, vol. Hv. p. 180. 



