i 
ss 
Bartow—A Mechanical Cause of Homogeneity of Crystals. 605 
Groups of identical composition which differ very greatly may 
generally be compared with the structure-isomerides of the chemist, 
but, as we shall notice immediately, cases are conceivable in which, 
while no enantiomorphous relations subsist, some considerable 
degree of resemblance exists between the different kinds of group- 
ing of the same set of balls, and which therefore have a more 
‘intimate connection than appears to subsist in cases of mere struc- 
ture-isomerism. 
In this connection an attempt at classification of isomers made 
by Hantzsch may be referred to. He says:— 
“Tt is difficult to characterize stereo-isomerides in a general 
manner; in attempting to do so we must substantially confine 
ourselves to the following :— 
Stereoisomerides as distinguished from structure-isomerides 
are generally more readily and mutually capable of transfor- 
mation one to the other. According to their behaviour they 
fall into the two following groups :— 
1. Substances displaying identity of all actual properties and 
differing only with regard to their action on polarized light, their 
* ontical activity,” called therefore optical or mirror-image isomeri-. 
des. These are substances whose atoms are at the same abso- 
lute distances apart in the molecule, but have a different order 
as to their arrangement; they may perhaps be named “ relative 
stereoisomerides.”’ According to theory such substances contain 
asymmetric atom complexes. Isomerides of this kind which contain 
but one asymmetric atom-complex are, with the single exception of 
their optical behaviour, absolutely identical. ‘Those with several 
asymmetric complexes may besides exhibit differences in their 
physical, and even to some slight degree in their chemical 
behaviour.” 
2. Substances which in spite of the identity of their structural 
formula and the behaviour thereby expressed, nevertheless exhibit 
differences in all physical and in certain chemical properties not to be 
expressed by structural formule, but are without action on polarized 
light.” * 
1See ante, pp. 594 and 596. * Compare p. 598. 
3 Hantzsch’s ‘‘ Grundriss der Stereochemie,”’ pp. 5 and 64. Compare Bischofi’s 
‘¢ Handbuch der Stereochemie,’’ p. 46. 
