1876.] 
Recent Chemical Researches . 
nature of the non-carbonated portion of the compound 
molecule : he professes himself unable to explain such vari- 
ations, except on the assumption that the carbon atom is 
possessed of great plasticity, and that it exists in combina- 
tion in different allotropic forms. Gautier has also obtained 
compounds of phosphorus in which that element appears to 
exist in the amorphous condition ; while Houzeau and 
Renard, by the action of ozone upon benzene, have produced 
a peculiar body which appears to contain oxygen in its allo- 
tropic form of ozone. We may therefore suppose that in 
the formation of isomeric compounds a transformation of 
one allotropic form of the dominant atom into another takes 
place, and that — inasmuch as such a transformation is ac- 
companied with changes in the potential and kinetic energy 
of the atom — the compounds will differ from one another in 
the amounts of energy which they contain, although the 
valency of the individual atoms may be the same in all. 
But considerations such as these lead us to speak of— 
IV. Groups of Compounds . 
And here we are, of course, met by the great fadt of the 
existence of isomeric compounds. We must regard the 
molecules of all substances as material systems. Now 
Prof. Clerk-Maxwell has said that when we can explain any 
phenomena as changes in the configuration and motion of a 
material system, we have given a complete dynamical ex- 
planation of these phenomena. We must therefore endeavour 
to explain the phenomena of isomerism as changes in the 
configuration or motion of the molecules of the isomeric 
bodies. The ordinary way of representing such changes is 
by placing the symbols which represent the atoms of the 
molecule in different relative positions in space in the dif- 
ferent formulae. Isomerism in this view is caused by a 
change in the position of the atoms. But we must remem- 
ber that no formula can give us a true insight into the con- 
stitution of the molecule ; the atoms are in a state of 
motion, each performing its own definite oscillation : our 
formulae represent them as at rest. Another explanation of 
isomerism has been sought for by supposing that different 
amounts of energy are concerned in the production of iso- 
meric bodies, and that these bodies therefore differ in the 
potential energy which they contain. Now if a greater 
amount of energy has been expended in the formation of the 
body A than in the formation of its isomer B, what has 
that energy been employed in doing ? Surely in altering the 
relative motions and configurations of the atoms. Therefore 
VOL. vi. (n.s.) g 
