14 INAUGURAL ADDRESS. 



but not in that of ionisation, where other influences seem to be at; 

 work. Hence we find a special difficulty arising in those frequent 

 dynamical investigations in which we deal with the interactions of 

 salts in aqueous solution ; for though we may determine the vary- 

 ing total concentrations of the salts, we often find ourselves unable 

 to ascertain what fraction of each is at any moment in the ionised 

 or active state. Here, then, there is need of new light. 



Perhaps the most genei'ally interesting result that has followed 

 from these dynamical studies is that the velocity of a chemical 

 change is often accelerated by the mere presence (so it would seem) 

 of molecules of some foreign substance which itself is quite 

 unaffected by the change. The acceleration may be positive or 

 negative ; that is to say, the action may be hastened or retarded ; 

 and the effect may be in some cases so great as to render an other- 

 wise imperceptibly slow change very rapid, or an otherwise rapid 

 change negligibly slow. Foreign substances which act in this way 

 are called " catalysers," and their action " catalysis." Special 

 cases of catalysis have been known to chemists for quite a long 

 time ; but modern dynamical work has proved that it is a much 

 more common phenomenon than was suspected. In fact, we are 

 inclined now to say that there is no chemical action which is not 

 susceptible to catalytic acceleration by some agent and that there is nO' 

 substance incapable of acting as a catalyser in some chemical change. 

 There has, of course, been much speculation as to the hoii> of cata- 

 lysis ; but, in spite of ingenious hypotheses, applicable to particular 

 cases, and a great accumulation of experimental evidence bearing 

 on the question, we are still pretty ignorant. Perhaps some day 

 w'e shall be wiser ; certainlv catalvsis is one of the problems of the 

 future. Meanwhile, I may mention that the so-called hydrogen 

 ions of acids and hydi'oxyl ions of alkalis (that is, the two ions which, 

 by their combination, form water) are among the most frequently 

 potent catalysers, and that the enzymes or chemical ferments of 

 physiological actions also come within the same category. This 

 last fact speaks eloquently for the interest which attaches to the 

 whole subject. 



Leaving molecules, let me say a little about the atoms which- 

 compose them. Of these there is not an unlimited, nor even a 

 very great, variety ; and oiily a few of those known occur largely 

 as components of molecules in the laboratory of nature. But, from 

 the standpoint of science, every species of atom, or-^to put it in 

 another way — every element, is of absolutely first rate importance ; 

 for each differs in some respects from all others, and each can teach 



