222 



HISTORY OF CHEMISTRY. 



[LECTURE xn. 



of two or three atoms of hydrogen, a cause is furnished for the 

 holding of these molecules together." Since an unlimited 

 number of heterogeneous molecules may unite in this manner, 

 even the. most complicated compounds could be referred to 

 types. There was thus no longer any necessity to have re- 

 course to conjugated compounds, and Kekule further points 

 this out : " The so-called conjugated compounds are not com- 

 posed in any manner different from other compounds; they 

 can be referred in the same manner to types in which hydrogen 

 is replaced by radicals ; they follow the same laws with respect 

 to their formation and saturating capabilities as hold for all 

 chemical compounds." 



With a view to facilitating a better comprehension of 

 Kekule's ideas, I give below a few of the formulae proposed 

 by him: 



- w H 



r ^ 5 referred/H 



H HJ 



Benzene sulphonic acid. 



H 



HI H 

 Qn -j referred /HJ SO.,1 



to \H\ SO 2 |O 



C A H 5 



o / H J 



referred 

 to 



HJ H j O 



HJ 



Sulfobenzide. Nordhausen sulphuric acid 



H 



etc. 



sojo 



Isethionic acid. Carbyl-sulphate. Sulfobenzoic acid. 



The way in which Kekule employs the reaction with penta- 

 chloride of phosphorus, in order to distinguish from each other 

 the types H 2 and H 2 O, is interesting, and I shall mention it 

 here in passing. Kekule points out how the oxygen in water 

 is replaced, by means of this reagent, by two atoms of chlorine, 

 whereby the molecules corresponding to this type are broken 



