450 SCIENCE PROGRESS. 



and so on ; so that as R iv gradually passes from the maximum 

 to the minimum the sign of the rotation changes four times. 

 These conclusions have been tested in the case of over 

 forty derivatives of amyl alcohol. If in amyl cyanide, 



CH 3 (i 5 ) 

 (2 9 )C 2 H— C— CH 2 CN( 4 o), 



H 



the largest group, CH 2 CN, be replaced by others of weight 

 exceeding 29, the molecule remains in almost every case 

 dextro-rotatory, and in most cases the rotation increases 

 with the mass, as shown by the following examples : — 



But on the other hand we have 



amyl alcohol -CH 2 OH(3i) = - 5 2' 



„ amine -CH 2 NH 2 (3o) = - 3" 30' 



,, aldehyde -COH (29)= +o°42'. 



So that the change of sign which should take place only 

 below 29 begins at 31. 



Thus, as Guye points out, the molecular dissymmetry 

 depends largely, but by no means exclusively, on the 

 weight of the groups. The study of other compounds 

 (esters of tartaric, glyceric, and valerianic acids) leads to the 

 same conclusion. In particular it is noticed that equality 

 in the weight of two different groups is not, as the formula 

 demands, accompanied by inactivity. Thus ethyl-malic 

 acid, 



CH 5 r /CHXOOH 

 COOH - H 



exhibits dextro-rotation, although C 2 H 5 0(45)= COOH(45). 

 Similarly amyl aldehyde remains slightly active, although 



COH( 29 )= C 2 H 5 (2 9 ). 



Again, propyl-glycerate is more active than iso-propyl- 

 glycerate. It might be supposed that this was due to the 



