214 PRESENT PROBLEMS OF INORGANIC CHEMISTRY. 



ferent conditions of temperature and pressure might result in the 

 greater stability of some forms which under our ordinary condi- 

 tions are changeable and unstal)le. The fact that under higher 

 ))ressures than are generally at our disposal ditferent forms of ice 

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

 such cases, will greath^ enlarge our Iviiowledge of molecular isom- 

 erism. 



The phenouHMia of catalysis have been extensively studied of 

 recent years, and have obviously an important bearing on such 

 jH'oblems, A catalytic agent is one which accelerates or retards 

 the velocity of reaction. Without iiKiuiring into the mechanism 

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

 ical change and to render stable bodies which under ortlinar}' con- 

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

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

 nizable rate of isomeric change may be made apparent and meas- 

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

 under ordinary circumstances, owing to its infinitesimal amount, 

 may be induced to exist in weighable quantity if the velocity of its 

 formation from an isomeride can be greatl}^ accelerated by the 

 presence of an apin'opriate catalytic agent. I am not aw^are 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 

 an}^ guide exists which would ena!)le us to predict that any particu- 

 lar substance would 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 

 velocit3^ It is possible, therefore, to cause ordinary reactions to 

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

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

 of the main reaction as regards their 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. l)ut what has been done for that compound may be 

 extended indelinitely to others, and. doubtless, with analogous re- 

 sults. Indications of the existence of as yet undiscovered compounds 

 may be derived from a study of i)hysical, and particularly of elec- 

 liical, changes. There appears to l)e sufficient evidence of an oxide 

 of hydrogen containing more oxygen than hydrogen dioxide, from 

 a study of the electromotive force of a cell containing hydrogen 

 dioxide; j^et the higher oxide still awaits discovery. 



The interpretation of chemical change in the light of the ionic 



