500 SCIENCE PROGRESS. 



molecular aggregates always result from the artificial for- 

 mation of active molecules. In fact in the molecule 

 C(R'),R"R" the forces acting between one R' radical and 

 the remaining radicals are the same as those between the 

 other R' and the remaining radicals ; hence each R' must 

 be at the same distance from each of the radicals CR"R " ; 

 that is, they are on a line drawn at right-angles to the plane 

 of CR"R" (or to the line CR"R" if this is a straight line), 

 and at equal distances on each side of that plane (or line). 

 It follows that when an R' group is replaced by R lv , the 

 exchange will be effected indifferently on either side of the 

 molecule, so that in the enormous number of exchanges 

 occurring in any chemical reaction, there will be as many 

 molecules attacked on one side as on the other, and we 

 shall have as many CR'R iv R"R'" molecules as CR iv R'R"R'" 

 molecules. The formation of equal quantities of right- and 

 left-handed molecules is therefore in complete accord with 

 the symmetrical configuration of C(R') 2 R'R". Given the 

 symmetry the equality in the quantities follows, and vice 

 versa. From this symmetry it follows further that sub- 

 stances of the formula C(R') 2 R"R'" will be inactive. This 

 is invariably the case. If in the active body C ■ CH 3 " CHJ • 

 H • C 2 H 5 we do but substitute H for I, forming C'(CH 3 ) 2 *H ■ 

 C 2 H 5 , inactivity results. This is another remarkable con- 

 firmation of the symmetry of the molecule C(R') 2 R"R"'. 

 Moreover it o^oes to show that this molecule is three- 

 dimensional, since it is very unlikely that the simple substitu- 

 tion of H for I should so profoundly modify the large molecule 

 of amyl iodide as to reduce it from three dimensions to two. 



The results we have thus far attained with regard to 

 asymmetry may be briefly summarised thus : — 



General law: Asymmetric molecules are such as contain 

 AR'R'R'", etc. 



Exceptions. Theory. I. Chaotic molecules. 



II. Plane molecules. 



III. Self-compensating molecules. 

 Exceptions. Found. I. II. and III. as above. 



IV. All substances (except per- 



haps limonene) in which A 

 is not a single atom. 



