610 Dr. D. Mendeleeff [May 31, 



surface contact, and involuntarily gives rise to conceptions of that 

 unity of the forces of nature which has been so energetically insisted 

 on by Sir William Grove and formulated in his famous paradox. 

 Grove noticed that platinum, when fused in the oxyhydrogen flame, 

 during which operation water is formed, when allowed to drop into 

 water decomposes the latter and produces the explosive oxyhydrogen 

 mixture. The explanation of this paradox, as of many others which 

 arose during the period of chemical renaissance has led, in our time, 

 to the promulgation by Henri St. Claire Deville of the conception of 

 dissociation and of equilibrium, and has recalled the teaching of 

 Berthollet, which, notwithstanding its brilliant confirmation by 

 Heinrich Rose and Dr. Gladstone, had not, up to that period, been 

 included in received chemical views. 



Chemical equilibrium in general, and dissociation in particular, 

 are now being so fully worked out in detail, and applied in such 

 various ways, that I do not allude to them to develop, but only use 

 them as examples by which to indicate the correctness of a tendency 

 to regard chemical combinations from points of view differing from 

 those expressed by the term hitherto appropriated to define chemical 

 forces, namely, " affinity." Chemical equilibria dissociation, the 

 speed of chemical reactions, thermo-chemistry, spectroscopy, and, 

 more than all, the determination of the influence of masses and the 

 search for a connection between the properties and weights of atoms 

 and molecules ; in one word, the vast mass of the most important 

 chemical researches of the present day, clearly indicates the near 

 a2)proach of the time when chemical doctrines will submit fully and 

 completely to the doctrine which was first announced in the Principia 

 of Newton. 



In order that the application of these principles may bear fruit it 

 is evidently insuflicient to assume that statical equilibrium reigns 

 alone in chemical systems or chemical molecules : it is necessary to 

 grasp the conditions of possible states of dynamical equilibria, and to 

 apj^ly to them kinetic principles. Numerous considerations compel us 

 to renounce the idea of statical equilibrium in molecules, and the 

 recent yet strongly supported appeals to dynamic principles consti- 

 tute, in my opinion, the foundation of the modern teaching relating 

 to atomicity, or the valency of the elements, which usually forms 

 the basis of investigations into organic or carbon compounds. 



This teaching has led to brilliant explanations of very many 

 chemical relations and to cases of isomerism, or the difference in the 

 l^roperties of substances having the same composition. It has been 

 so fruitful in its many applications and in the foreshadowing of 

 remote consequences, especially respecting carbon compounds, that 

 it is impossible to deny its claims to be ranked as a great achieve- 

 ment of chemical science. Its practical application to the synthesis 

 of many substances of the most complicated composition entering into 

 the structure of organised bodies, and to the creation of an unlimited 

 number of carbon compounds, among which the colours derived from 



