277 



substitute i> occupied by the new one, or by one of tin- tin., 

 already present. 



Werner makes a suggestion to account for the phenomenon 

 1>\ supposing that the other substitutes have a guiding inllun- 

 which tries, by means of attraction, to bring the new substitute 

 int<> the range of the three others; the mechanism, as proposed 

 by this author, does not involve any reference to the fact that 

 one group would take the place formerly held by anotl 



The most recent investigations of Debye 1 ) on the molecular 

 structure of the graphite-crystal, made by means of R on t gen- 

 rays, throw some new light also on the problem under conside- 

 ration. Debye was able to demonstrate that the carbon-atom 

 not only acts with four equal valencies which are directed in 

 space as supposed by Van 't Hoff, but that this atom can 

 also act with three valencies of equal strength, while the fourth 

 is considerably reduced in comparison with the others, acting in 

 a direction perpendicular to the plane of the last, and with only a 

 very slight intensity. If this be true, we might suppose that during 

 the chemical process a passing detachment of the radical takes 

 place, and that as soon as the new substitute arrives, the resti- 

 tution of this fourth reduced valency into the original state of 

 four equal valencies can occur towards the one or towards the 

 other side of the plane of the three others, both these events 

 finally leading to two enantiomorphous tetrahedron-configurations. 



Such an intermediate detachment of the radicals round the 

 asymmetric atom, but under simultaneous formation of ethylene- 

 derivatives, was also previously proposed by N e f 2 ) in his explana- 

 tion of phenomena of re-arrangement in general. It still however 

 remains unexplained why such a change of place does not always 

 lead to complete racemisation, as both antipodes have the same 

 mechanical stability. 



However, all these suggestions can hardly be considered other- 

 wise than made "pour besoin de la cause", and to be hypotheses 

 which in general appear quite arbitrary, although perhaps they are 

 useful in some special cases. Frank land, in his summary of 

 the facts up till now observed with respect tot the remarkable and 

 highly important phenomenon of the W aide n-in version, is un- 



1) P. Debye; cf. note on p. 152. 



2) J. U. Nef, Journ. Amer. Chem. Soc. 80. 647. (1908). 



