W. A. Norton on Molecular Physics. 205 
No. of this Journal (1865), lays down the following law of de- 
composition: ‘Bodies which evolve heat in being decomposed_ 
by heat are not again formed in the subsequent cooling.”  Ac- 
cording to what has just been stated all such bodies must evolve 
heat because of the electric condensation that attends the forma- 
tion of new compound molecules, after the primitive molecules 
have been decomposed. Now if these new molecules be cooled, 
the tendency would be to increase the molecular attraction by 
which their constituents are held together, rather than to favor 
their decomposition. The instances cited, viz: protoxyd of ni- 
trogen, peroxyd of hydrogen, chlorous and chloric acids, the 
chlorid, iodid, and sulphid of nitrogen, seem to sustain this ex- 
planation. 
is no formation of new molecules following the first decom posi- 
tion, and that the heat which may be absorbed in addition to 
that consumed in the act of separation, is due solely to an expan- 
sion taking place after the receding molecules have been urged 
beyond the limit of molecular attraction, and become subject to 
molecular repulsion. In that event, a subsequent cooling, by 
contracting the atmospheres of the molecules and so increasing” 
of platinum, and certain other metals upon gases, and of sur- 
faces generally upon aqueous vapor, with evolution of heat (see 
this Journal, vol. xxxviii, p. 109), may be referred to a polariza- 
tion developed by the mutual action of the surface and the gas or 
va 
Combination by Volume.—The assumption is now generally 
the gaseous state 
Occupy the same volume. This conclusion to which chemists 
have been conducted, implies that there are the same number of 
Molecules in equal volumes of different substances, and therefore 
that the elastic tension of the individual molecules, is the same 
for all gases. This result corresponds with the determination of 
