Conductors of Electricity, and during Electrolysis. 269 



when corrected, and reduced on account of the dissolution of 

 oxide of zinc, was 0, 84. 



37. In this instance the mean resistance was 0*32 ; whence, 

 by a calculation precisely similar to those given under Exps. 

 1 and 2, we have the theoretical amount of heat = 0°*74. 



38. The three instances above given, are specimens taken 

 from a number of experiments with the platinized silver pairs. 

 The mean of the eight unexceptionable experiments which 

 I have made with them, gives 2°*08 of actual, and 2°*13 of 

 theoretical heat, and not one of the individual experiments 



E resented a greater difference between real and calculated 

 eat, than Exp. 2. 



39. Exp. 4. — A plate of copper, four inches broad, was 

 bent about a plate of amalgamated zinc three inches and a 

 half broad, so as to form a pair of Wollaston's double battery. 

 It was placed in a jar containing two pounds of dilute sul- 

 phuric acid. In this instance, the total voltaic heat that was 

 generated was 1°*2, the calculated result being 1 0, only. 

 Repeated experiments with the copper pairs gave similar 

 results, the real heat being invariably somewhat superior 

 to that which the doctrine of resistances would demand. 

 The cause of this I have found in a slight local action, which 

 it is almost impossible to avoid in the common copper bat- 

 tery. 



40. Exp. 5. — I now constructed a single pair on Mr. 

 Grove's plan. The platinum, two inches broad, was immersed 

 in an ounce and a half of strong nitric acid contained by a 

 4-inch pipe-clay cell ; the amalgamated zinc plate, also two 

 inches broad, was immersed (at the distance of an inch and 

 a half from the platinum) in thirty ounces of sulphuric acid, 

 sp. gr. 1156. The whole was contained by one of the jars 

 (22.). 



41. A trial, made first as usual, in order to ascertain the 



4*4 0'S16 



resistance of the pair, gave -qr^jjg = r , . Q6 > whence 



r = 0*441 . As soon as the slight heat acquired during the 

 above trial was equably diffused through the apparatus, the 

 thermometer placed in the dilute sulphuric acid stood at 

 51°*95, the temperature of the air being 52°*4. The circuit 

 was then immediately closed for ten minutes, during which 

 time the needle of the galvanometer advanced steadily from 

 68° 40' to 71° 20'; the mean deviation being 70° 9' = 4°'77 Q. 

 As soon as the heat thus generated was equably diffused*, 



• By gently stirring the dilute sulphuric acid with a feather, so as to 

 bring every part in successive contact with the porous cell during two 

 minutes. 



