450 



SCIENTIFIC THOUGHT. 



In 1874 two chemists, Le Bel and Van't Hoff, suggested 

 independently a picture of the tetravalent carbon atom, 

 which would explain how it could enter with its four 

 points or capacities of saturation into two compounds 

 having the same saturating substances, but arranged in 

 ways which were not geometrically superposable, but only 

 symmetrical, like a right- and left-hand glove, or the 

 48. images in a mirror. The suggestion amounts to this, 



The carbon 



tetrahedron, that the carbon atom has the shape of a tetrahedron, 

 the four corners representing the four valencies or capa- 

 cities of saturation. 1 



The carbon tetrahedron is the last step which has been 

 taken in the development of the atomic view of matter 

 and of nature. No book on organic chemistry can now 

 well avoid introducing this and other similar ways of 

 representing chemical relations. On the further special- 

 isation of this conception will probably depend to a large 

 extent the future of our chemical theory i.e., of our at- 

 tempts to grasp the qualitative nature of different sub- 

 stances. It is clear that we are far on the way to realising 

 Wollaston's prophecy of the year 1808 viz., "that the 



1 This speculation was at first 

 looked upon with very great doubt. 

 Only few chemists of note took it 

 up ; others, such as Kolbe, who led 

 a consistent opposition to the ideas 

 and developments of structural 

 chemistry, treated it with ridicule. 

 Van't Hoff, ten- years after the 

 publication of the first edition of 

 his pamphlet, ' La Chimie dans 

 1'Espace' (Rotterdam, 1875) re- 

 viewed the position in his ' Dix 

 Anndes dans 1'Histoire d'une The- 

 orie' (translated by Marsh, Oxford, 

 1891), and, after reproducing the 



two opposite reviews, with which 

 the original theory was met by 

 Wislicenus and Kolbe, was able to 

 state " that the theory in question 

 now forms part of elementary 

 chemical teaching, and is to be 

 found enunciated in the most 

 widely used text-books" (transla- 

 tion, p. 19). Further applica- 

 tions of the theory, especially to 

 the compounds of nitrogen, will be 

 found in the 2nd edition of the 

 German translation ' Die Lagerung 

 der Atome im Raume' (Braunsch- 

 weig, 1894). 



