284 Prof. Norton on Molecular Physics. 



of approximation of the elementary particles and other parti- 

 culars. 



The relations of heat to chemical phenomena may be deduced 

 from the principles already stated. The heat of combination 

 results from the condensation of the electric sether that takes 

 place between the uniting particles, and from the compression of 

 their individual electric atmospheres — one or both of these effects. 

 Both of these effects should give rise to an emission of universal 

 sether in heat-pulses. 



But, according to Pavre and Silbermann, certain substances 

 combine with an attendant absorption instead of an evolution of 

 heat. To understand how this may happen, we must observe 

 that, according to the received ideas of the true nature of che- 

 mical processes, the molecules of all substances are composed of 

 two or more atoms associated together; and when two substances 

 combine, it generally happens that one or both of the two mole- 

 cules presented to each other is decomposed, and two new com- 

 pound molecules are formed by condensation. Now the decom- 

 position that precedes the combination should occasion a loss of 

 heat by reason of the expansion of the electric sether condensed 

 between the constituent molecules (or " chemical atoms "), and of 

 the atmospheres of these molecules ; and the subsequent combi- 

 nation by the reverse process should develope heat. Tf the loss 

 of heat from the one cause exceeds the gain from the other, 

 there will be an effective absorption of heat as the result of the 

 combination. On the other hand, when chemical combination 

 occasions an evolution of heat, it is in general because the heat 

 absorbed while the decomposition of individual molecules is 

 going on, is afterwards more than restored by the heat deve- 

 loped in the combination that succeeds the decomposition. Thus 

 when oxygen and hydrogen combine to form water, heat is 

 evolved because, as we conceive, much less heat is lost in the 

 decomposition of the binary molecule of oxygen than is pro- 

 duced in the union of the two separated molecules (chemical 

 atoms) of oxygen, each with a molecule of hydrogen. In some 

 instances, as in the formation of the hydrate of lime, the mole- 

 cules would seem to combine without any previous decomposi- 

 tion, and any tendency, therefore, to absorption of heat. In the 

 decomposition of substances, as well as in their combination, it 

 is found that heat may either be absorbed or evolved. This 

 fact admits of a similar explanation to that just given. M. 

 Schroder Van der Kolk, in a memoir " On the Mechanical 

 Energy of Chemical Action," a translation of which is given in 

 the April Number of the Philosophical Magazine (1865), lays 

 down the following law of decomposition : — " Bodies which evolve 

 heat in being decomposed by heat are not again formed in the 



