* 
Physics and Chemistry. 93 
which is formed to the temperature of the components before combina- 
tion, the steam will contain a quantity of energy less than that of its 
components by the quantity which is given out in the combination, We 
heat is given out in the decomposition, in the second, it is absorbed. It 
e when we 
iments of Favre and Silbermann. These physicists found that protoxyd 
of nitrogen, NO, peroxyd of hydrogen, HO,, chlorous and chloric acids, 
10, an O,, evolve heat during decomposition, while the elements 
eparated do not recombine on cooling. The same is true for the gt 
G 
‘on heating pass into a different physical state, with evolution of heat, the 
Previous state is not resumed on cooling. It is of course possible that in 
“certain cases the purely chemical-affinity between the molecules may be so 
powerful that combination will ensue, heat being abstra from the sur- 
founding medium. The converse proposition is as follows’: 
_ If heat be absorbed in decomposing a body by means of heat, the —— 
_ dary action will take place on subsequent cooling. ae 
_ This proposition ants demonstrated theoretically, and is therefore 
