308 Professor William J. Pope [May 1, 



unless some power of selection of an enantiomorpbous nature is exer- 

 cised in replacing X by Q, tbe doctrine of cbance will ensure tbe 

 one X group being replaced tbe same number of times as tbe otber in 

 an enormous number of tiny molecules. Tbus tbere will result just 

 the same amount of tbe rigbt-banded optically active substance as of 

 its left-banded isomeride. When an optically active substance is 

 prepared in tbe laboratory it is tberefore obtained as a mixture of 

 two enantiomorpbously related isomerides ; such a mixture is said to 

 be compensated, because tbe right-handedness of the one component 

 is just counterbalanced by the left-handedness of the isomeric con- 

 stituent. These compensated substances are represented by the third 

 tetrahydroquinaldine previous referred to but not further discussed. 



Since one of the great problems with which cbemistry is grap- 

 pling involves the synthetic preparation of naturally occurring 

 optically active substances, it is of the utmost importance that the 

 chemist should be in possession of working methods for resolving 

 these compensated mixtures into their optically active components. 

 All kinds of methods applicable to such resolutions necessarily involve 

 the introduction of enantiomorphism — either of method or of material. 

 Three types of method were introduced by Pasteur, namely, (1) 

 spontaneous resolution by crystallisation, (2) resolution by combina- 

 tion with optically active substances, and (3) resolution by the action 

 of living organisms. 



The first kind of method depends upon the fact that on crystallis- 

 ing a compensated substance it sometimes deposits crystals of the 

 dextro- and the laevo-isomeride side by side, and of such size that 

 they can be mechanically sorted. The enantiomorpbous factor 

 determining the separation in this kind of method is obviously the 

 enantiomorpbous intelligence which has tbe power of discriminating 

 between right and left-handedness. This sort of method is, un- 

 fortunately, but rarely applicable, owing to the fact that two 

 enantiomorpbously related substances usually crystallise together in 

 the form of a loose chemical compound. 



The second kind of Pasteur method is applicable to the resolution 

 of compensated acids and bases, and depends upon the following con- 

 siderations. On combining a compensated basic substance, viz. a mix- 

 ture of d-B and 1-B,* with an optically active acid, say d-A, a mixture 

 of two salts, namely, d-B, d-A and 1-B, d-A, will be obtained. These 

 salts, however, are not enantiomorpbously related, as will be realised 

 on substituting, for illustrative purposes, a band for the base and a 

 glove for the acid. The combination d-B, d-A will then be repre- 

 sented by a right hand in a right-handed glove, wbilst the combina- 

 tion 1-B, d-A will correspond to a left hand in a right-handed glove. 

 The struggles of tbe left band with tlie right-banded glove will not 

 be a factor in determining the behaviour of the ajipropriately sorted 

 right hand and right-handed glove. So also, the properties of the 



* The prefixes dextro- and la3Vo- are conveniently abbreviated to the initials 

 d- and 1-. 



