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racemic compound is associated with a certain temperature limit, 
and this is also the case in the solid condition. Thus, for 
example, it is only above 28°, the temperature of interconversion, 
that the racemate is, formed from dextro- and laevo-sodium~ 
ammonium tartrate; while at temperatures below this the con- 
verse process takes place. Racemic combinations behave in this 
respect therefore like salts which contain water of crystallization 
and particularly resemble double salts in their relation to the 
two components, in that both production and separation of the tie 
are connected with certain definite conditions of temperature.’’! 
We may further quote from van ’t Hoff as showing how neces- 
sary for chemical action it is that the configurations of the groups | 
which come together shall be adapted to one another. “The 
chemical identity of the two active tartaric acids, which ismanifested 
in every case of their combination with an optically-inactive sub- 
stance, ceases to show itself directly optically-active substances 
take part in the reaction. Thus, for example, the acid 
ammonium salt of dextro-tartaric acid combines with the acid 
ammonium salt of laevo-malic acid to form a readily crystallizing 
double salt, whilst on the other hand the acid ammonium salt of 
the laevo-tartaric acid will not enter into combination with the acid 
ammonium salt of laevo-malic acid. Dextro-tartaric acid combines 
with laevo-asparagine to form a crystalline salt, but laevo-tartarie 
acid will not combine with asparagin; and other examples can be 
called to mind.” ? | 
The formation of groups in the way indicated above,’ admits 
of very wide application, and if there is some considerable vari- 
ation of the conditions, we shall expect frequently, even where 
no asymmetry is present, to encounter some variety in the kind 
of group produced from a given set of balls. Variety thus pro- 
duced which does not spring from any enantiomorphous relations, 
will, however, be very much of the nature of the polymorphism 
previously treated of, and we may expect the properties of the 
different groups formed of the same set of balls to differ greatly, in- 
deed in some cases almost as much as those of groups of different sets. 
604 Scientific Proceedings, Royal Dublin Society. 
1 « Grundriss der Stereochemie,’’ pp. 32, 33. 
2 Van ’t Hoff, ‘‘Lagerung der Atome im Raume,’’ 1877 ed., p. 42. 
3 See p. 586. 4 See p. 575. 
