Bartow—A Wechanical Cause of Homogeneity of Crystals. 607 
' words less likely, that dimorphous arrangements productive of 
isomerism will be presented. 
Perhaps chemical saturation is akin to closeness of packing,? 
and if so, we may, for comparison with the conclusion just stated, 
cite the fact that no stereochemical situation-isomerism has 
hitherto been detected in saturated compounds of identical struc- 
ture, from which it would appear that under given conditions but 
one single equilibrium position is capable of a lasting existence.” 
That the stereoisomerism of unsaturated compounds has 
identity substituted for it in the corresponding saturated com- 
pounds is illustrated by the experimental fact that with the 
greatest precautions one and the same succinic acid is obtained by 
the reduction of fumaric acid and maleic acid alike.® 
Before bringing to an end these observations on the effects 
produced by the presence of groups, a few more words should be 
said about resemblances existing between groups composed of 
different sets of balls.* 
Groups which are differently arranged may, whether their 
composition is the same or not, bear a partial resemblance which 
causes some similarity of behaviour. 
As a case in point we may take that of groups whose resemblance 
consists in their having the same kind or kinds of balls outermost. For 
one of the effects of agiven kind of ball or set of balls lying outer- 
most in a group will manifestly be that the balls thus situated will 
be more exposed to separation from the group and recombination 
of a different kind than if their place were in the interior, and 
groups resembling one another in the way referred to will, there- 
fore, have some properties in common. 
With this may perhaps be compared the suggestion that the 
separation of water in the case of dibasic acids, such as phthalic 
acid and maleic acid, is associated with near proximity of the 
hydroxyl groups.* 
1 See page 680. ? Hantzsch’s ‘‘ Grundriss der Stereochemie,”’ p. 61. 
3 Tbid., p. 90. 
* A general conclusion respecting groups of slightly different composition which 
have a certain resemblance has already been stated. See p. 591. 
-> Compare Bischoff in Berl. Ber., xxiii., p. 620, and in ‘‘ Handbuch der Stereo- 
chemie,”’ p. 118; also Hantzsch’s ‘‘ Grundriss der Stereochemie,’’ pp. 67 and 101. 
SCIEN. PROC. R.D.S., VOL. VIII., PART VI. 24 3'G 
