to the Symmetry of Homogeneous Structures. 115 



With this may be compared such a fact as that sodium 

 chlorate, which is optically inactive in solution, can be ob- 

 tained in a dextro- or laevo-rotatory form at will. 



Class 4. 



To those among the substances that rotate the plane of 

 polarization both when amorphous and when crystalline 

 which owe the property, as displayed in the solid state, to 

 complex intercalation of individual crystals, we find a paral- 

 lel in 



Homogeneous structures which, like those of Class 1, while 

 unbroken contain effective configurations of two opposite kinds 

 whose effects just cancel one another, but which, after being 

 symmetrically partitioned and dislocated, contain but one kind, 

 the other being destroyed in the process of dislocation; and 

 which also like those of Class 2, when differently orientated twin 

 individuals of them are inter calcated, form additional effective 

 configurations where the twinned individuals meet, but not in 

 two kinds which are enantiomorphs. 



Type 49 * will furnish an example of this if the following 

 conditions obtain : — 



a. The particles which furnish the effective configurations 

 in the amorphous state, i. e. after partitioning and dislocation 

 have taken place, form enantiomorphous 6-point-sets whose 

 centres in the unbroken structure are a set of the principal 

 singular points, i. e. of those lying at the intersections of 

 trigonal and digonal axes. 



b. These particles are so placed that the 6-point-sets of 

 opposite hand which, in the unbroken structure, they also 

 form f, and whose centres constitute another set of principal 

 singular points, are practically enantiomorphous to the first- 

 named 6-point-sets, and the circular polarization produced by 

 one set of 6-point-sets neutralizes, on the whole, in the un- 

 broken structure, that of opposite rotation produced by the 

 other set. 



c. Intercalation of twinned individuals, similar to that 

 described as occurring in Class 2, produces, as in that case, 

 effective configurations where the individuals meet. 



The origin of the circular polarization displayed in the 

 amorphous state is in this class different from that to which 

 it is traceable in the twinned condition. 



A new and striking instance of this class of circular 

 polarization is given by Pope in the paper already referred 

 to J, viz., £rans-7r-camphotricarboxylic acid. 



* Zeitschr.f. Kryst. xxiii. p. 31. 



t Comp. p. 112. 



\ Trans. Chem. Soc. 1896, pp. 972 and 978. 



