214 PRESENT PROBLEMS OF INORGANIC qHEMISTRY. 



ferent conditions of temperature and pressure might result in the 

 greater stability of some forms which under our ordinary condi- 

 tions are changeable and unstable. The fact that under higher 

 pressures than are generally at our disposal different forms of ice 

 have been proved to exist, and the application of the phase rule to 

 such cases, will greatly enlarge our knowledge of molecular isom- 

 erism. 



The phenomena of catalysis have been extensively studied of 

 recent years, and have obviously an important bearing on such 

 problems. A catalytic agent is one which accelerates or retards 

 the velocit^y of reaction. Without inquiring into the mechanism 

 of catalysis, its existence may be made to influence the rate of chem- 

 ical change and to render stable bodies which under ordinary con- 

 ditions are unstable. For if it is possible to accelerate a chemical 

 change in such a way that the usually slow and possibly unrecog- 

 nizable i-ate of isomeric change may be made apparent and meas- 

 urable, a substance the existence of which could not be recognized 

 under ordiiuiry circiunstances, owing to its infinitesimal amount, 

 may l)e induced to exist in weighable quantity if the velocity of its 

 fonnation froui an isomeride can be greatly accelerated by the 

 preseuce of an appropriate catalytic agent. I am not aware that 

 attempts have been made in this direction. The discovery of cata- 

 lytic agents is, as a rule, the result of accident. I do not think that 

 any guide exists which would enal)le us to predict that any particu- 

 lar substance Avould cause an acceleration or a retardation of any 

 particular reaction. But catalytic agents are generally those which 

 themselves, by their power of combining with or parting with 

 oxygen, or some other element, cause the transfer of that element 

 to other compounds to take place with increased or diminished 

 velocity. It is possible, therefore, to cause ordinary reactions to 

 take place in presence of a thii'd body, choosing the third body with 

 a view to its catalytic action, and to examine carefully the products 

 of the main reaction as regards tlieir nature and their quantity. 

 Attempts have been made in this direction with marked success; 

 the rate of change of hydrogen dioxide, for example, has been fairly 

 well studied. But what has been done for that compound may be 

 extended indefinitely to others, ancb (h)ubtless, with aiudogous re- 

 sults. Indications of the existence of as yet undiscovered compounds 

 may be derived Ironi a study of physical, and particularly of elec- 

 trical, changes. There tippears to l)e sufficient evidence of an oxide 

 of hydrogen containing more oxygen than hydrogen dioxide, from 

 a study of the electroniDtive force of a cell containing hydrogen 

 dioxide; yet the higher oxide still awaits discovery. 



Tlie interpretation of chemical change in the light of the ionic 



