498 Mr. J. P. Joule on the Heat disengaged 



23*38 divisions of the scale of the thermometer employed are 

 equal to one degree of the Centigrade scale, we obtain for the 



A — C 



quantity of heat due to -r — 5 x BC, 



OO'/O I'D/ / <& -ir»r>o iv 1 Afr'O o 



23138 x 1^542 x 12837= 1455°-3. 



The quantity of heat actually evolved will be 



lQ.l iq 



o™ x H79-2=963°-99. 



Subtracting the latter from the former result, we obtain 491 0, 3 

 as the quantity of heat absorbed in the electrolysis of a quantity 

 of sidphate of copper corresponding to 0'5874 of a gramme of 

 copper. The quantity of heat absorbed per gramme of copper 

 deposited will therefore be 836 0, 4. 



Two other series of experiments conducted in precisely the 

 same manner, excepting that in the former of the two the spe- 

 cific heat of the solution was obtained by the method of mixtures, 

 gave, for the absorption of heat per gramme of copper deposited, 

 respectively 856° and 796 0, 5. The mean of the three results 

 is 829°-6. 



The above quantity of heat is that absorbed in separating the 

 copper and oxygen gas from a solution of sulphate of oxide of 

 copper. It is therefore necessary to subtract the absorption due 

 to the transfer of the sulphuric acid from the oxide of copper to 

 water, in order to obtain the heat absorbed in the decomposition 

 of oxide of copper into metal and oxygen gas. For this purpose, 

 8 grammes of oxide of copper, prepared by adding potash to a 

 solution of the sulphate of copper, and then carefully washing 

 and igniting the precipitate, were thrown into an acidulated 

 solution of copper similar to that used in the above experiments, 

 the capacity for heat of which had been previously ascertained. 

 The mean of four experiments, tried in this way with every pos- 

 sible precaution, gave 236° as the heat due to the solution of 

 1*252 gramme, the quantity of oxide corresponding to a gramme 

 of copper. 



829°-6-236°=593°-6 = the quantity of heat absorbed in 

 the decomposition of oxide of copper into copper and oxygen 

 gas, and which ought therefore to be the quantity of heat evolved 

 by the combustion of a gramme of copper. 



Combustion of Zinc. 



My experiments on this metal were similar to those on copper ; 

 they will not therefore require a veiy detailed description. The 



