THE ELECTROLYSIS OF WATER. 10i 
though it is difficult to ascertain with precision 
the quantity of heat evolved by the solution of 
oxide of copper in dilute sulphuric acid, I am 
persuaded that it is not less than 3° nor more 
than 4° per equivalent. Suppose it to be 3°5= 
0°571 of resistance to electrolysis. Then 1:702 
~0°571=1:131,* the intensity due to the sepa- 
ration of oxide of copper into metal and gas. 
But 0°731 represents the intensity of the union 
of non-gaseous oxygen with copper: therefore 
1:131—0°731=0°4, a result not widely different 
from that obtained with zinc. We may, I think, 
take 0°45 as a near approximation to the intensity 
due to the gaseous state of oxygen. 
As we have already stated that 1 is the inten- 
sity necessary to separate oxygen from hydrogen, 
and to give the latter the gaseous state, 1°45 is, 
according to the above calculations, the intensity 
required to electrolyze water. This is not widely 
different from 1°35, the mean of column 11:— 
0°45 of resistance to electrolysis is equal to 2°76. 
It would be curious to ascertain whether the same 
amount of caloric could be evolved by the mecha- 
nical condensation of eight grains of oxygen gas. 
* See note page 100. 
