in Chemical Combinations. 501 



Hence 245 7°-7 — 1565° = 892°-7 = the quantity of heat ab- 

 sorbed in the electrolysis of a quantity of sulphate of zinc cor- 

 responding to 0-5861 of a gramme of zinc. 



The quantity of heat absorbed by the electrolysis of a quantity 

 of sulphate of zinc corresponding to a gramme of zinc will there- 

 fore be 1523°-1. 



The results of two other series of experiments, conducted in 

 precisely the same manner as that I have just given, were 1547° 

 and 1619° respectively. The mean of the three results is 1563°. 



The heat absorbed by the transfer of the sulphuric acid from 

 the oxide of zinc to the water was ascertained in the following 

 manner. A solution of zinc similar to that employed in the 

 experiments was acidulated with about 10 grammes of sulphuric 

 acid. 7'9 grins, of oxide of zinc (prepared by igniting the car- 

 bonate) were thrown into this solution ; and the heat evolved by 

 its union with the free sulphuric acid was carefully ascertained, 

 and properly corrected for the influence of the atmosphere. The 

 capacity for heat of the jar of solution was then ascertained by 

 the method of electrical currents. This being done, a fresh 

 quantity of oxide of zinc was thrown into the solution, and the 

 heat evolved again observed. The mean of the two experiments 

 gave 378° for the quantity of heat evolved by the solution of 

 1'242 grm., the quantity of oxide of zinc corresponding to a 

 gramme of zinc. 



1563° — 378°= 1185°, the quantity of heat absorbed in the 

 decomposition of oxide of zinc into zinc and oxygen gas ; and 

 which ought therefore to be the quantity of heat evolved by the 

 combustion of a gramme of zinc. 



Combustion of Hydrogen Gas. 



The apparatus employed in the experiments on hydrogen is 

 shown in fig. 8. a represents a glass jar nearly full of a solu- 

 tion consisting of six parts of water and one of strong sulphuric 

 acid, and containing platinum electrodes ; b represents a glass 

 tube for conveying the mixed gases to the pneumatic trough c. 

 The glass stirrer d, being inserted in the small cork e, can, when 

 not in use, be made perfectly tight by inserting the latter into 

 the large cork which stops up the mouth of the jar. A coating 

 of a viscid solution of rosin in turpentine was applied wherever it 

 appeared necessary, in order to ensure perfect tightness. The 

 quantity of mixed gases evolved was ascertained by the weight 

 of water displaced in the bottle f; and hence the weight of libe- 

 rated hydrogen was computed with the assistance of the best 

 tables, regard being paid to the temperature of the gas, its hy- 

 grometric state, the barometric pressure, &c. 



