142 HISTORY OF CHEMISTRY. [LECTURE VIII. 



and the formation of benzoic acid from bitter almond oil is 

 explained in the same way : 



CH 10 O 2 .H, + O 2 = C 28 H 18 O 2 .O + H 2 O. 



Bitter Almond Oil. Benzoic Acid. 



In order to be able to include the action of oxygen within 

 his rule, he states the latter as follows : When a compound 

 is exposed to the dehydrogenising action of any substance, it 

 takes up a quantity of this substance equivalent to the quantity 

 of the hydrogen eliminated. 



The doctrine of Dumas seems to me to be of most im- 

 portance in this connection. He shows us that equal volumes 

 of hydrogen, chlorine, bromine, and iodine are equivalent, 

 while they possess only half the value of the same volume of 

 oxygen. The difference between the two is clearly visible 

 here, and this is the beginning of the separation of atom and 

 equivalent. 



The phenomena of substitution, or of metalepsy, as Dumas 

 called it, were followed up further in the succeeding years by 

 Dumas himself, as well as by Peligot, 35 Regnault, 3 * 3 Malaguti, 37 

 and, especially, Laurent ;-and in particular, it is the independent 

 extensions which the latter gave to Dumas' rule, that we shall 

 now consider. 



Laurent has enriched chemistry with a very large number 

 of experimental investigations, but these, in many cases, are 

 unfortunately wanting in the necessary accuracy. He had 

 at his command only very limited resources, and instead 

 of confining himself, on that account, to a few branches, 

 Laurent, who was very fertile in ideas, preferred to start a great 

 many things and to carry them out in a superficial manner. 

 He destroyed, in this way, his reputation as an experimentalist, 

 and was met with hostility at the very outset of his scientific 

 activity ; while he was afterwards treated with unnecessary 

 severity, especially by Berzelius and Liebig. This naturally 



35 Annalen. 12, 24 ; 13, 76 ; 14, 50 ; 28, 246. 3S Ibid. 17, 157 ; 28, 

 84 ; 33, 310 ; 34, 24, etc. 37 Ibid. 24, 40 ; 25, 272 ; 32. 15 ; 56, 268, etc. 



