74 Proceedings of the Royal Society 
potassium and chlorine, each occupying its individual volume 
unchanged, but it would alter greatly the heat evolved in so doing. 
If oxygen combined with chloride of potassium as a whole, with¬ 
out any condensation taking place, the natural result would he an 
evolution of heat. But if the addition of the oxygen diminishes 
the co-efficient of contraction, as compared with that of the free 
compound, then we have a physical explanation of the evolution 
of heat on decomposition. In this case the actual work performed 
by the condensation of oxygen is retained in a potential form, and, 
therefore, reappears as heat on its decomposition. If, now, we 
examine the mode in which the oxygen is attached to the respec¬ 
tive halogen compounds, we can trace, as a necessary consequence, 
the retention of varying amounts of energy. Chlorate, bromate, 
and iodate of potash are formed by a similar chemical reaction, 
according to the following formula of exchange, given in equiva¬ 
lents, the whole reaction supposed to take place in the presence of 
water:— 
6KO + 
6C1 = 5KC1 + 
£C10 6 
6(76238) 
5(97086) 
6KO + 
6Br = 5KBr -f 
KBr0 6 
6(76238) 
5(85666) 
6KO + 
61 = 5KI + 
KIO s 
6(76238) 
5(72721) 
We have appended the thermal equivalents attending the for¬ 
mation of these bodies in a large volume of water. It will be 
obvious on comparing the formation of chlorate of potash, through 
the above reaction, that it may be the result of absorption of heat; 
whereas it is certain that the formation of iodate of potash must 
be attended with an evolution of heat, or else cold must be the 
result of their action. In special experiments, made with the 
object of determining the thermal action, neither absorption nor 
evolution of heat could be detected. Thus the formation of iodate 
of potash is attended with an evolution of heat. This would, then, 
accord with the easy transformation of the chlorates into iodates, or 
of chloric acid into iodic acid, and the easy transformation of the 
iodide of potassium into the iodate, through the action of perman¬ 
ganate of potash, seeing that we must have an evolution of heat. 
