600 Scientific Proceedings, Royal Dublin Society. 
according to what has just been said above, we should look for in 
assemblages related in the way described, is actually presented — 
when there are several isomers. We thus find isomers distinguished 
as stable and Jabile, and presenting physical and, to a slight 
extent, chemical differences.’ 
We find, too, that the process of change under change of con- 
ditions, such as rise of temperature, is complicated by the greater 
variety possible where there are more than two isomers enantio- 
morphous to one another. Thus van’t Hoff says :—‘‘ As shown 
on page 41, compounds containing a single asymmetrical carbon 
atom when heated yield an inactive mixture corresponding to the 
stable equilibrium described. Compounds having two or more 
asymmetrical atoms show a different behaviour. It is manifest 
that in this case also the inactive mixture corresponds to the equi- 
librium which is finally arrived at, but two steps are generally 
requisite to reach this ultimate goal, for in general one of the two 
or more atoms accomplishes the transformation more quickly, and 
consequently under conditions which leave the rest yet unaltered. 
Starting, therefore, from the compound + 4+ B we obtain at 
first a mixture of +4+B,and+A-B. And taking into con- 
sideration that the quantities of the two products formed at the 
end of the first phase are by no means the same—indeed the two 
molecules, which are not as to their structure mirror-images of one 
another, will in general manifest a different degree of stability-— 
we shall not be surprised to find that in the case of the transfor- 
mation in question almost the entire mass comes to consist at first 
of + A—B; it may be with the reversal of the sense of the optical 
rotation. This result has in fact been observed.’” 
Racemic mixtures * of those isomerides which are strict enantio- 
morphs, that is to say, 
(+4+8B) with (-A-B) 
and (+ 4-8) with (-A+3B) 
—_—__. 
1 <¢ Grundriss der Stereochemie,”’ pp. 5, 87,43. ‘‘ Stéréochimie’’ par van’t Hoff, 
&c., pp. 50, 53 et esq. 
2 ‘‘ Stéréochimie,’’ par van ’t Hoff und Meyerhoffer, p.57. Comp. Pasteur’s words 
respecting the changes of quinine derivatives in Compt. Rend., xxxvii., p. 110. 
3 See pp. 596, 608. 
