•382 THE CANADIAN NATURALIST. fVol. 



Vll. 



fication. All the compounds derived by substitution from the 

 tjame body were ranged in the same family, of which the latter 

 was, so to speak, the chief. Hence arose groups of bodies per- 

 fectly distinct from each other, and the number of which were 

 belag constantly increased by daily discoveries. It was uecessciry 

 rndt only to introduce order into all these tribes, but to connect 

 ■'them with each other by a common bond. The honour of hav- 

 . ;ing discovered the superior princii^le of classification belongs to 

 fLaurent and Gerhardt, valiant champions of French science, from 

 ^^vliom premature death has snatched, if not victory, at least the 

 gratification of victory. Laurent was the first to say that a certain 

 number of mineral and organic compounds possessed the constitu- 

 tion of water, and this idea, brilliantly developed by Williamson, 

 was generalised by Gerhardt. According to the last named, all 

 inorganic and organic compounds may be connected with a small 

 Mramber of types, of which hydrochloric acid, water, and ammonia, 

 ■are the chief. In these compounds, relatively simple, one ele- 

 ment may be replaced by another element, or by a group of atoms 

 performing the function of a radical, so that this substitution 

 gives rise to a multitude of various compounds bound together 

 by the analogy of their structure, if not by the harmony of their 

 properties. 



This last point was novel and important. Bodies belonging 

 to one type and similar in their molecular structure may difi"er 

 much in their properties: these depend not only on the arrang*'- 

 ment of the atoms, but also on their nature. Thus the inorganic 



. and organic bodies ranged under the type water, are, accordinu 

 to the nature of their elements or their radicals, powerful bases, 

 energetic acids, or indifierent substances — a great and bold idea, 

 which has established a connection between the most diverse 

 bodies, and which has definitely overturned the barriers which 

 use had raised, and which the weakness of theory had maintained, 

 between inorganic and organic chemistry. And yet this was 

 only a stage in the march of ideas. By what right and by what 

 privilege, it was said, may the relatively simple compounds wc 

 have named serve as types for all others, and why should nature 



• be restricted to make all bodies on the model of hydrochloric 

 acid, water, and ammonia ? This was a serious difficulty, but it 

 has been removed ; it became the occasion of a profound discus- 

 sion and the germ of a real progress. 



Those typical compounds represent at bottoui various forms 



