152 SCIENCE PROGRESS 



saw the coming of a new day in organic chemistry. He pro- 

 posed to change the name of the compound radicle : it should 

 no longer be called benzoyl, it should be called Proin, or Orthrin 

 (jrpwl = the beginning of the day ; 6p6p6^ = daybreak). 



An examination of the chemical memoirs published in the 

 thirties and forties of last century shows that chemists were 

 constantly forced to use the conceptions and the language of 

 the atomic theory, even when they tried to confine themselves 

 to the skinniest descriptions of the facts, and more especially the 

 facts about isomerism and allotropy, that were daily added to 

 the science. 



During the thirties of last century Dumas began his study 

 of the replacement of hydrogen by chlorine in organic com- 

 pounds, and the relations between the parent compounds and 

 their derivatives, a study which tended towards the fixing of 

 the vague notions about substitution that had for long been 

 simmering in the minds of many chemists. Dumas tried to go 

 no further than the assertion that, as a matter of fact, one 

 equivalent of hydrogen can be replaced, in many organic com- 

 pounds, by one equivalent of chlorine. Then he said that in 

 many cases this replacement is accompanied by " maintenance 

 of the chemical type." But what does ** maintenance of the 

 chemical type" mean? many chemists — notably Laurent — de- 

 manded. Dumas replied : 



" I consider as belonging to the same chemical type those 

 substances which contain the same number of equivalents united 

 in the same manner, and have the same fundamental chemical 

 properties." 



He produced formulas of several pairs of compounds, each 

 pair of which he declared to belong to the same chemical type. 

 But as neither he nor any other chemist could give a clear, 

 workable meaning to the word equivalent, nor form a mental 

 picture of " equivalents united in the same manner," his formu- 

 las were sentences of a language which bristled with vague 

 hypotheses while it pretended merely to express facts. 



Some years earlier, Dumas had made a bold attempt to 

 reconcile the notions of the simple atom and the compound 

 atom ; he had even tried to apply the notion of the compound 

 atom to the elements. But the facts of gaseous combinations, 

 many of which were captured for chemistry by Dumas himself, 



