Dr. Beetz on the Electromotive Force of Gases. 83 



the Grove's circuit was placed in a cup of mercury, so that 

 the current in r" could be closed by rapidly immersing the 

 second wire of the galvanometer in this cup. The length of 

 b was then fixed by the running clamp-screw of the instru- 

 ment for measuring the resistance, and a altered until the 

 needle of the galvanometer G on closing the circuit /" remained 

 at 0. We then have 



F = i— y/^. 



a+R-f6 



To find R, b then obtained another value V ; a then became 

 a', so that 



F = 



a' + R + ^> 



R was calculated from both equations. In the present in- 

 stance this method is very convenient, and sufficiendy exact 

 also, when the circuit to be measured is not too inconstant (as 

 that in which hydrogen and oxygen are used). The follow- 

 ing series of experiments show that this point was attended 

 to. By a controlling measurement made by Ohm's method, 

 I convinced myself of the applicability of the above process. 

 Lastly, to ascertain the force ^', the measuring platino-zinc 

 circuit was closed by the wire of the rheochord in which a 

 had been previously measured, the needle of the galvanometer 

 was then driven to 24°, which deflection I had found to cor- 

 respond to an evolution of 13*36 cubic centimetres on an ave- 

 rage of the mixed gases in the proportion for forming water 

 per minute. When the necessary resistance was p, we had 



Z:' = R + p, 



where unity is that electromotive force, which, with a re- 

 sistance of one centimetre German silver wire of 8*689 spe- 

 cific gravity (the average of four weighings), a centimetre of 

 which weighs 0*00683 grm. (the mean of five determinations), 

 evolves 13*36 cubic centimetres of the mixed gases per minute. 

 With this value of unity, the force of the platino-zinc circuit 

 is about =42. From these determinations the values found 

 may be readily compared with any others. Ifi for example, 

 we convert the measurements made by M. PoggendorfF from 

 his unit, in which the force of the Grove's circuit is about 

 = 32, into mine, this force becomes 42*27. A measurement 



k". 

 24-02 



