Mr. Joule on the Electrical Origin of Chemical Heat. 205 
Quantities converted into Dulon g’s |My own Ex} Theoret. |Corrected Theore- 
Protoxides. Results. | periments.| Results. tical Results, 
40 ars. of Potassium...].......s00s: 176 21°47 
33 grs. of Zinc... ...... 10:98 11:03 13°83 11-01 
oe OTS. OL ILO: ss dees ae 9-00 9:48 12°36 8:06 
31°6 grs. of Copper ...| 5°18 |............ 9°97 5°97 
1 gr. of Hydrogen | 898 | 836 | 10-47 10:40* 
In the above table there is one metal, copper, of which I did 
not treat in my former paper; it will therefore be well to explain 
the manner in which the theoretical results for it were obtained. 
Platinum wires were immersed in a saturated solution of the 
sulphate of oxide of copper. These were successively con- 
nected with the poles of voltaic arrangements consisting of 
various numbers of Smee’s pairs in series. Using two pairs, 
I had neither current nor decomposition. But with three 
there were electrolytic effects, oxygen being evolved from the 
positive, and copper being deposited on the negative electrode. 
The ratio of current passed by three and four pairs was as 
nearly as possible 1:4. Therefore 22 pairs are equal to the 
resistance to electrolysis of sulphate of oxide of copper. 
Now if I calculate, as I did in my former paper for zinc, iron, 
and hydrogen, I must argue that electricity equal in intensity to 
that of 23 pairs passes between oxygen and copper when they 
unite by combustion. But one pair of Smee’s battery can pro- 
duce electricity of such intensity that a degree+ of it will evolve 
3°°74 of heat, and multiplying by 22 we have 9°97, the 
quantity of heat which is evolved by a degree of electricity 
of 2% times that intensity; 9°97 is therefore the theoretical 
result, if we suppose that the intensity required to overcome 
the resistance to electrolysis of sulphate of oxide of copper is 
equal to the intensity of current arising from the union of oxy- 
gen and copper in combustion. 
There is, however, since the experiments of Daniell, reason 
to think that this is not the case, but that part of the z:ztensity 
of a current engaged in electrolyzing these compound bodies, 
is used in separating the acid from the base prior to or (ac- 
cording to that philosopher’s view) simultaneously with the 
decomposition of the latter. Unfortunately we cannot bring 
forward a direct experiment in proof of this fact, inasmuch as 
* I now find that Prof. Daniell has proved the remarkable fact, that 
during the electrolysis of dilute sulphuric acid one quarter of an equivalent 
of acid goes along with the oxygen to the positive electrode. According 
to this the corrected theoretical result is 10°47 ; one quarter of the heat 
evolved by the union of water and sulphuric acid equal about 9°47. 
+ My degree’of electricity is the quantity necessary to electrolyze an 
equivalent expressed in grains, as nine grains of water, &c, 
