168 VELOCITY OF KEACTION, AND 



ing with another molecule, which also may require similar changes 

 in its molecular constitution before it is fitted to react; and (2) the 

 physical forms of energy which act between the dissolved molecule 

 and its solvent, such as the velocity of movement of the molecule 

 through the solvent, and, at any rate in the case of the colloidal 

 molecule, probably surface tension at the surface between the 

 dissolved molecule and its solvent. 



Action between the dissolved molecule and its solvent, which 

 must also come in as a factor in preparing for chemical reaction, or 

 altering the resistance to chemical reaction, is seen in the different 

 ionising powers of different solvents for salts, and in the different 

 degrees of association of different dissolved substances in different 

 solvents. For example, the ionisation of inorganic salts in water 

 as compared to organic solvents, and the duplicate and higher 

 molecular weights of organic substances in an associating solvent, 

 such as benzol, compared with another solvent, such as alcohol. 

 As proof of this connection, it may be pointed out that the more 

 ionised a dissolved substance is the more quickly it reacts, showing 

 that the molecular resistance to reaction has been broken down; 

 and the very different velocities of reaction of the same substances 

 in different organic solvents must be due to corresponding 

 differences in molecular resistance to reaction in these different 

 media. 



The first of these factors is that which will probably be most 

 effective in entirely stopping a reaction, and the latter that which 

 is effective in rendering reactions in solution as a general rule much 

 slower than those which occur in gaseous mixtures. 



It is by modifying the action of these opposing forms of energy, 

 in some way, 1 that the catalyst or enzyme or living cell produces 



1 The mode of action is at present unknown to us : the hypotheses thereon 

 will be given later; the important fact to realise here, apart from any hypo- 

 thesis, is that the catalyst acts as an energy conductor or transformer for 

 chemical energy, and varies the amount of energy necessary to be trans- 

 formed into other channels before the reaction can ensue. It only makes 

 the path easy between forms of energy. Further, it may be pointed out 

 that the modus operandi of energy transformers lies always without the pale 

 of our knowledge in the case of other forms of energy, just as much as in the 

 case of chemical energy, where the matter has given rise to so much thought 

 and discussion. We do not really know, for example, the mode in which an 

 electric current heats a wire, or how an electric current magnetises iron, and 

 no other substances; all we have is hypothesis, just as we have for how a 

 catalyst produces its transformations of chemical energy. 



