244 



This arrangement is not very probable, but its possibility cannot 

 be at present denied, because we do not know anything as to how the 

 chemical forces between the substitutes act, and such a contest of 

 attracting and repulsing forces may be imagined, which would exactly 

 produce the rather strange and certainly very rare arrangement 

 foreseen in this connection. 



It will be clear from this, that in each of the supposed cases, the 

 plurivalent central atom would be only partly asymmetrical, if the 

 last word is used in the meaning of Van 't Hof f's theory: for in the 

 case first mentioned, the non-superposable arrangement exists, 

 but not the contrast in chemical nature of the asymmetrically arran- 

 ged substitutes; in the second case, the chemical differences between 

 the substitutes, as postulated by Van 't Ho f f and Le Bel, are pre- 

 sent, but the arrangement of the whole is in this hypothetical molecule 

 such as to make the occurrence of two non-superposable, isomeric 

 molecules impossible here. The last case may be almost accidental, 

 but of the first several instances are now known and have been 

 already sufficiently studied, as we shall soon see. And in this case 

 it has indeed been fully confirmed that the optical activity of the 

 moleciile is not so much due to the chemical contrast between the 

 substitutes round the central atom, as to the degree of symmetry, 

 or dissymmetry, of their arrangement in space. 



From this it appears necessary in all problems in the domain 

 of stereochemistry, to find out in each case : what is the influence 

 of the one, and what of the other of the two factors considered above? 



We must investigate whether in the case ot Pasteur's law, the 

 observed properties of the molecule are principally governed by 

 the non-superposable arrangement of the constituent radicals, or 

 by their chemical contrast, or by both causes. Only when we shall 

 have succeeded in separating both these factors out of the fullness 

 of their common manifestations, we can hope to get a clearer insight 

 into the true significance of Pasteur's law, and of the part played 

 by Van 't Hoff-Le Bel's suggestive theory in explaining it 1 ). 



17. With respect to the fact that the occurrence of optical 

 antipodes can also take place, when only the arrangement of the 

 atoms is different from its mirror-image, independently of the special 

 circumstance that certain chemical differences of the substitutes 



x ) F. M. Jaeger, Proceed. Ron. Akad. v. Wet. Amsterdam, 17, 1217, (1915); 

 18, 49, (1915); Chemisch Weekblad, 14, p. 706732. (1917); 20, 244, 263, (1917); 

 Receuil des Trav. Chim. des Pays-Bas, 38, 171, (1919). 



