760 
MR. BRODIE ON THE CONDITION OF CERTAIN ELEMENTS 
force de combinaison qn’ils exercent les uns sur les autres est grande et plus aussi 
les proprietes de leurs composes different de celles de leurs elements. C’est la un 
probleme dont je ne pourrais entreprendre la solution qu’en traitant de I’influence de 
relectricite sur la matiere.” 
This view, although the received doctrine, has not passed quite unquestioned. 
Ampere invented a molecular theory, which led him to conclusions inconsistent with 
it. For reasons not of a chemical nature only, but which had reference prin- 
cipally to the propagation of light and sound and to other physical phenomena, he 
had arrived at the idea that in every chemical substance there were what may be 
called three forms of matter, the indivisible atom, the molecule or system of atoms, 
and the particle or system of molecules. He conceived, moreover, that every gas 
contained in the same space an equal number of these molecules. From this it was a 
necessary inference, that in that contraction which takes place when oxygen and hy- 
drogen combine to form water, a division must take place of the elemental molecule. 
He considered that the oxygen divided, half a molecule of oxygen combining with 
each molecule of hydrogen*. On this view therefore the atoms, even of the elements, 
formed what was in a certain sense a compound group. The discovery of isomeric 
forms of hydrocarbon in different states of condensation, and of other similar facts, 
gave rise to new ideas as to the possible differences of bodies, and explanations simi- 
lar to that by which the differences between certain isomeric organic bodies have 
been accounted for came to be applied to the case of the elemental bodies themselves. 
Thus the allotropy of sulphur has been explained by assuming it, in its various forms, 
to be the same substance in different states of condensation, in which case the dif- 
ference between these forms might be expressed by giving to them the different che- 
mical formulse of S, S.^, S3. Those physical relations however of density and specific 
heat, which might give a true scientific value to such speculations, and prove that 
these substances were really thus connected, have not yet been made out to exist ; nor 
indeed has any fact been discovered which places such a notion beyond a conjecture. 
Graham again, to explain the mode in which the metals conduct electricity in the 
voltaic circuit, assigns to these bodies what he terms a sali-molecular structure, and 
regards them as consisting of two atoms of a chlorous or acid combined with one atom 
of a zincous or basile element, “ the three atoms of the molecule being of one metal 
and of the same nature'!'.” The latest work in this direction is a paper of M. Lau- 
rent, in which he has attempted, among other»things, to account for the differences 
in the different classes of salts of the same metal in which, hitherto, different oxides 
of a different degree of saturation have been supposed to exist, by assuming them to 
contain different molecules or atomic groups of the metal ; and he has shown how, on 
this idea, our classification of chemical substances maybe much simplified; on this 
* Annales de Chimie, vol. Iviii. p. 434. See also Gerhaedt, Comptes Rendus des Travaux de Chimie, 1847, 
p. 90, note. 
t See Graham’s Chemistry, Ed. 1842, pp. 226 and 541, 
