250 HISTORY OF CHEMISTRY. [LECTURE XIII. 



as possible, but he does not proceed to introduce types corre- 

 sponding to these states. 



It was in 1857, on the occasion of the discussions respect- 

 ing the constitution of mercury fulminate, that Kekule 3 first 

 stated that the constitution of this substance, as well as that 

 of the other compounds of the methyl series, may be referred 

 to the marsh gas type, C 2 H 4 ; and to the latter type mercury 

 fulminate is, according to Kekule's experiments, to be reckoned 

 as belonging. 4 



He therefore writes : 

 C 2 H 4 C 2 H 3 C1 CjHClg C,(N0 4 )C1 3 



Marsh gas. Methyl chloride. Chloroform. Chlorpicrin. 



C 2 (N0 4 ) 2 CL, C 2 H 3 (C,N) C,(C,N)(N0 4 )Hg, 



Marignac's Oil. 5 Acetonitrile. Mercury fulminate. 



A beginning had thus been made, but still the type C 2 H 4 was 

 only of very little use. So long as it could not be extended to 

 all carbon compounds, there could be no question of making it 

 the basis of a system of organic chemistry such as it afterwards 

 actually became. The idea which rendered this possible was 

 still wanting. Kekule had perhaps already conceived it at the 

 time, and merely did not-dare to publish it ; or it may be that 

 the hypothesis of the linking of carbon atoms had not yet 

 occurred to him. In any case, the views which he then held 

 must have approximated very closely to those which he pub- 

 lished in 1858 concerning the nature of carbon, for, at the end 

 of 1857, when he refers the types to the different valencies 

 of the elements, 6 he definitely mentions the quadrivalence of 



3 Annalen. 101, 200. 4 [C = 6, O = 8.] Kekule here employs these 

 atomic weights again, whereas he had discarded them as inaccurate four 

 years previously. Kolbe (J. pr. Chem. [2] 23, 374) regards as important 

 the fact that Kekule then pointed out that he did not employ the word 

 type "in the sense of Gerhardt's unitary theory, but in the sense in which 

 it was first employed by Dumas upon the occasion of his fruitful investiga- 

 tions on the types." I consider this unimportant, more especially as Kekule 

 proceeds as follows: "I shall indicate the actual relations in which the 

 substances mentioned stand to one another, by saying that, under the 

 influence of suitable agencies, the one can be produced from, or converted 

 into, the other." 5 Annalen. 38. 16. 6 Ibid. 104, 129. 



