146 HISTORY OF CHEMISTRY. [LECTURE VIII. 



Laurent into our ordinary language. It will then be possible 

 to obtain, moreover, a better grasp of Laurent's ideas. 



The nucleus theory clearly sprang from the radical theory, 

 but only by an essential reconstruction of the latter. The 

 radical of Laurent is not an unalterable group of atoms, but it 

 is a compound, which can be altered by substitution in equiva- 

 lent proportions and does not lose thereby its characteristic 

 properties. Thus Laurent is able to derive all his radicals from 

 hydrocarbons, a proceeding which is, of course, in complete con- 

 tradiction to the older ideas. These radicals can unite with other 

 atoms, and in the substances so produced the nuclei are present 

 as such ; the nuclei pre-exist in the substances, and Laurent, 

 therefore, entirely agrees on this point, with his predecessors. 

 By means of these two hypotheses, he is able to explain all the 

 facts not only the cases which follow Dumas' rule, but those 

 also which are at variance with it, and of the latter he had found 

 a large number. At the same time, his point of view furnishes 

 reasons why both kinds of reactions are possible. On the assump- 

 tion of the alterability of the radical, it may easily be understood 

 that a group included far more compounds than was possible 

 with the older radical theory. Laurent was thus able to discover 

 far more of what we should now call " generic relationships," and 

 that was an unquestionable advantage. Since he assumed the 

 number of carbon atoms in the nucleus to be constant, sub- 

 stances were arranged into series according to the number of 

 atoms of carbon they contained, and this supplied the basis of 

 an excellent systematic classification. With him there was no 

 connecting link between the series so formed ; and in this 

 respect Laurent's division differs from the classifications of the 

 present day, which accentuate all relationships as much as 

 possible. No such mode of treatment could, indeed, have been 

 carried out at that time. 



After these explanations, I may state that much that was 

 new and good was advanced in Laurent's nucleus theory. Its 

 importance lies principally in the fact that it was capable of a 

 general application, and, as Gmelin proved, could be admirably 

 employed as the basis of a detailed text-book. In this respect it 



