BarLtow—A Mechanical Cause of Homogeneity of Crystals. 601 
have been synthetically obtained in the case of the borneols, 
phenylurethanes and the camphoric acids.’ 
As to the diminution, just now referred to, of the number 
‘of possible combinations when the asymmetrical grouplets 
contained in a composite group are not all of different 
kinds, we may compare the facts cited by van ’t Hoff and others,’ 
and especially that as to the production of the inactive indivisible 
type of the composition (4 +B) + (- A- B) or (A- B) + (- 4+ B), 
the inactivity arising from the intramolecular compensation, and 
being distinct from the inactivity produced by oe enantiomor- 
phous molecules.° 
The most familiar example is furnished by the isomerism of 
the tartaric acids. Thus in this group we find the two isomers 
with similar opposite rotation, also their inactive mixture, racemic 
acid, which was separated into its two constituents by Pasteur. 
But what in particular distinguishes the case in question is the 
existence of an indivisible inactive isomeride, which was also dis- 
covered by Pasteur, and which Przibytek* some time ago in vain 
sought to divide. 
Several compounds may besides be mentioned whose constitution 
approximates more to the tartaric acids in so far as they, like the 
latter, are distinguished by a symmetrical formula and two asymme- 
trical atoms. These bodies deserve particular attention because 
they always furnish a case of isomerism which, according to the 
old views, is inexplicable. Most of these compounds have only 
recently been investigated, principally by Bischoff.° 
The packing of a given asymmetric grouping will,in some cases, 
be closer when one of the two kinds of enantiomorphs alone is 
1 « Stéréochimie’’ par van’t Hoff u. Meyerhoffer, p. 56; and as to less symmetrical 
mixtures, p. 57, e¢ seg. Comp. ‘‘Grundriss &c.,’’ p. 39, et seg. 
2 « Stéréochimie ’’ par van ’t Hoff, &c., p. 61. 
3 Comp. Hantzsch, ‘‘ Grundriss &c.,”’ pp. 20, 26, and 45. 
4As Hantzsch remarks:—‘‘In the two dextro and laevo tartaric acids the two 
asymmetrical complexes - CH(OH) COOH must have configurations of the same 
sense, but in the inactive indivisible tartaric acid one of them must have the opposite 
sense to that of the other. (See ‘‘ Grundriss &c.,’’ p. 44.) 
5 Berl. Ber., xvii., 1412. 
6 «¢ Stéréochimie,”’ par van ’t Hoff, &c., p.63. Comp. “‘Lagerung der Atome im 
Raume,”’ 1894 ed., p. 838, and Hantzsch’s ‘‘ Grundriss &c.,” pp. 24 and 26. 
