Fig. 3. 



Conductors of Electricity, and during Electrolysis. 267 



fered materially from the rest, I have found that the total 

 corrected heat produced by the dissolution of 100 grains of 

 the oxide of zinc in sulphuric acid, is able to raise two pounds 

 of water 3 0, 44. 



30. Exp. 1.— I constructed a single voltaic pair, consisting 

 of thin plates of amalgamated zinc and platinized silver (Mr. 

 Smee's arrangement) : the plates were two inches broad, and 

 were kept one inch asunder by means of a piece of wood, to 

 the opposite sides of which they were bound with string: to 

 the top of each plate, a thick copper wire formed a good me- 

 tallic connexion, by means of a brass clamp. The voltaic 

 pair, thus prepared, was immersed in two pounds of sulphuric 

 acid, sp. gr. 1137, contained by one of the earthenware jars 

 (22.). The arrangement is represented by fig. 3. 



31. When the circuit was completed so 

 as to present to the current the total metallic 

 resistance 0*06, the galvanometer stood at 

 49±° m 1°-84Q; and at \lf = 0°-453 Q, 

 when the total metallic resistance was in- 

 creased to 1*16 by the addition to the circuit 

 of ten feet of thin copper wire. Hence, ac- 

 cording to the principles laid down by Ohm, 



1-84 0-4-53 c ,. , t , 



= : from which r, the re- 



r + 1-16 r + 0'06 



sistance of the voltaic pair, = 0*299. Imme- 

 diately after this trial, the temperature of the 

 liquid being exactly 49°, and that of the air 

 50 0, 2, the circuit was completed for one hour, during which 

 the needle first advanced a little from 50°, and then declined 

 to 46°, the average* deviation was 48° 44' = l°-8 Q. The 

 temperature of the liquid was then 53 0, 7, indicating a rise of 



1*59 0'382 



4 0, 7- Another trial now ave , — — — - = -. — — - — ; whence 



r'+l-16 r'+0-06 



? J , the resistance of the pair at the close of the experiment, 

 = 0*288: the mean resistance of the pair was therefore 

 0-293. 



32. Now in order to obtain the total amount of heat evolved 

 by the pair, reduced to the capacity of two pounds of water, 

 we have4°-7 + 0°-4 (on account of Cor. A (21.)) and — 0, 5 

 (on account of Cor. B (22.)) = 4°-6. The correction due to 

 the dissolution of oxide of zinc is found by multiplying its 



* During each experiment the deflections of the needle were noted 

 at intervals of five minutes, or less. From thence I deduce my ave- 

 rages. 



