and the Theory of Chemical Types. 191 



experience to teach us; if it was false, it was experience which 

 would pronounce its falsity. In all cases it was necessary to 

 leave time to determine its place in science. 



The theory of types was scarcely published when the same 

 criticisms were reproduced, at least by M. Berzelius ; and not- 

 withstanding all my devotion to the interests of the science, 

 I would again have left to time and experience the care of 

 pronouncing on these debates. 



But when I reflected, it seemed quite evident to me, that 

 as a consequence of the researches of organic chemistry, ge- 

 neral chemistry had reached one of those periods of crisis, 

 when everyone owes to science the testimony of his convictions. 



We cannot conceal from ourselves that two systems of 

 ideas are before us: one, which is supported by all the au- 

 thority of the past, the rights acquired by quiet possession 

 now for nearly a century, the tacit assent of a great number of 

 chemists, and which reckons amongst its defenders and at their 

 head, a philosopher illustrious amongst the most illustrious, 

 M. Berzelius ; the other, which consists in asserting that 

 the bodies formed of the same number of chemical equivalents 

 placed in the same manner, belong to the same molecular 

 type, and often to the same chemical type. 



This latter attributes to the number and arrangement of 

 the particles an influence of the first order, which in the ideas 

 of the received chemistry belongs especially to the nature of 

 those particles. The law of substitutions would be the ex- 

 perimental demonstration of this new system, and would have 

 led some of its partizans to adopt it. I do not claim its in- 

 vention, for it does but reproduce and give precision to, under 

 a more general form, opinions which are to be found in the 

 writings of great chemists, and particularly MM. Robiquet, 

 Mitscherlich, Liebig, Laurent, Persoz, Couerbe, &c. It is pre- 

 cisely this coincidence between the numerous facts, to the dis- 

 covery of which the law of substitutions has led, and the opi- 

 nions already known relative to the influence of certain pre- 

 existing molecular arrangements, that has given me the con- 

 fidence necessary for their adoption in my turn when I pro- 

 posed the admission of organic types. 



Here we have, then, before us two systems : one which at- 

 tributes the principal agency to the nature of the elements, 

 the other which reserves it for the number and arrangement 

 of the equivalents. 



Pushed to an extreme, each of them in my judgement 

 would be found to lead to an absurdity. Regulated by ex- 

 perience and kept by it within prudent limits, each of them 

 must take a large share in the explanation of chemical phae- 



