4 
} 
| 
Bartow—A Mechanical Cause of Homogeneity of Crystals. 597 
The salts of tartaric and racemic acids respectively generally 
contain different proportions of water of crystallization, so that 
their crystal forms are not comparable, and but few cases are known 
in which the racemic form of a substance crystallizes with the 
same proportion of solvent as its optically active components. One 
such case has, however, been described by Armstrong and Pope.? 
Three modifications of sobrerol may be obtained, 7.e., laevo-, dextro-, 
and para-sobrerols. The two active modifications have identical 
chemical properties, and crystallize in hemimorphic monosym- 
metric prisms; the crystals of these optical antipodes are conse- 
quently enantiomorphous. On crystallizing a mixture of equal 
weight of each, holohedral orthorhombic crystals of the racemic 
modification are obtained. A very intimate crystallographic 
relationship exists between the crystalline forms of the active and 
inactive substances, as will be seen from the axial ratios given 
below. 
Active sobrerol (monosymmetric), a:b:e (B88 s 3) 0:85381 
Inactive sobrerol (Orthorhombic), GONG ak 2 1 : 0°8268 
Again, suppose :— 
2. That a homogeneous assemblage contains several different kinds 
of grouping of its balls which are not identical with their own mirror- 
images, aud that the various synimetrical groupings are separated by 
tracts or films of balls so constituted as to be identical with their own 
mirror-image. 
When this is the case, it is possible for the same balls to form 
other homogeneous assemblages which, together with the given 
assemblage, are all connected by the property that all correspond- 
ing distances between nearest centres are identical throughout the series 
of assemblages. or, if in any such assemblage any one of these 
asymmetrical groupings is removed, anda similar complex enautio- 
morphous to it substituted and similarly placed, no alteration in 
the distances separating nearest centres, when these distances are 
taken collectively, will be thereby made. And, therefore, a 
1 Journ. Chemical Soc., 1891, p. 315. 
2 Quoted from Pope’s translation of Fock’s ‘‘ Chemical Crystallography,” p. 150. 
