2 4 8 SCIENCE PROGRESS 



a spiral because three of them are identical, and so there will be 

 a break. The same is also true of the direction b — N. 



In the type Na 2 bcx, stereo-isomerism is possible, as the two 

 identical radicals a, a may lie opposite or contiguous to each 

 other at the base of the pyramid. The evidence of facts is 

 inconclusive. Schryver and Collie 1 first succeeded in pre- 

 paring two crystalline modifications of dimethyl-ethyl-ammonium 

 chloro-platinate; but there is no evidence to prove that the 

 phenomenon is not due to dimorphism, which was shown to be 

 present in the last case. Other attempts in this direction have 

 been equally unsuccessful. 



In both the possible isomers a smooth path is possible for 

 the polarised ray along N — x, because, in that case, the line 

 joining the other four groups a, a, b, c will not be a continuous 

 spiral, as two of the groups are identical, and so there will be a 

 break. So substances of this type will not show optical activity, 

 and none has been observed so far. 



In all the three cases we have so far considered, the theory 

 is quite open so far as stereo-isomers (other than optical isomers) 

 are concerned. The absence of such in each case can be ex- 

 plained by Jones's hypothesis, referred to above, viz. that the 

 most stable configuration is produced ; but if in future facts are 

 discovered proving conclusively the existence of such isomers, 

 we have simply to drop this assumption, without making any 

 other changes in the general conception. 



An interesting case, apparently similar to but really quite 



different from the last one above considered, is that of amino- 



oxides : 



a\ a\ /OH 



b-)N = O or b-)N< 

 c/ c/ \OH 



In 1908 Meisenheimer 2 showed that methyl-ethyl-aniline 

 oxide could be resolved into two active components. But at 

 that time it could not be decided whether the free active bases 

 were true amino-oxides or the corresponding di-hydroxy-com- 

 pounds, the general tendency of chemists being in favour of 

 the di-hydroxy constitution. But recently Meisenheimer 3 has 

 proved that these substances are optically active When dissolved 



1 Proc. Chem. Soc. 1891, 39. 



2 Ber. 41, 3966 (1908). 



3 Annalen, 385, 117 (191 1). 



