an 
— 
Atomic Volume of some Minerals. 245 
4 
The Gerhardtian principle that protoxyd bases replace per- 
oxyds, is also, when true, only a special case. The relations of 
the feldspars do not appear to be explicable on Gerhardt’s princi- 
ple; nor the relations of the varieties of scapolite or horublende. 
V. Species of the same atomic volume may be wholly unlike 
in crystallization, and hence volume alone does not seem to de- 
termine the form. Quartz has the atomic volume (C) of the feld- 
Spars—an interesting fact in view of their frequent association— 
and the A relation between it and albite is 1:6; yet there is no 
isomorphism between them. The fact that the two forms of a 
dimorphous substance differ but little in the calculated atomic vol- 
ume, (often much less than one of the forms differs from another 
isomorphous with it,) appears to be a case in point. Yet if in- 
stances of dimorphism are also instances of isomerism, it is pos- 
sible that the volume may actually be double that which is de- 
uced. We have much therefore, to ascertain on this point, 
before we can determine the true relation of form to volume. 
VI. There are difficulties in the way of applying these princi- 
ples to some compounds, arising from doubts with regard to the 
atomic weights. But, as in the case of hydrogen, (which is 
doubled by the Berzelian school,) these investigations seem to 
afford data for arriving at the truth. 
VIL. Since the relations of atomic volume are exhibited through 
the volume of the elemental molecules of compounds, it may be 
inferred that the elemental molecules are not combined together 
or united with one another in a compound ; but that, under their 
mutual influence, each is changed alike and becomes a mean re- 
sult of the molecular forces in action. If the elemental mole- 
cules were actually combined, as is usually supposed, the atomic 
volume of the aggregate should be the atomic volume of the com- 
pound ; so that in all comparisons between different substances, 
these aggregate results should present the true relation. ut, i 
appears that the true atomic volume relation is found in the ele- 
mental molecules of compounds, and much less clearly or uDi- 
formly in the aggregate results. This inference is at variance with 
received ideas on chemical combination; yet if our premises are 
Correct—we admit they need farther investigation—we see not 
how to avoid it. : 
_ We add an additional word upon the name applied to isomorph- 
ism among unlike compounds. Heleromerism, as stated, is un- 
meaning, this term being the correlative of isomerism, which has 
no relation to isomorphism. Heteromerous isomorphism is in 
itself applicable ; but the word isomerous is in use, and heterome- 
tous, if employed at all, should correspond in signification. As 
he above terms are therefore objectionable, we suggest as appro- 
priate and significant, the expressions isonomic and heteronomic 
tsomorphism ; the isomorphism being 1n one case between homol- 
©g0us substances, or those of like law or proportion in constitu- 
tion,—and in the other between substances unlike in constitution. 
° 
