4o POPULAR SCIENCE MONTHLY. 



usually slow and possibly unrecognizable rate of isomeric change may 

 be made apparent and measurable, 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 greatly 

 accelerated by the presence of an appropriate catalytic agent. I am 

 not aware that attempts have been made in this direction. The dis- 

 covery of catalytic agents is, as a rule, the result of accident. I do not 

 think that any guide exists which would enable us to predict that any 

 particular 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 velocity. 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. But what has been 

 done for that compound may be extended indefinitely to others, and 

 doubtless with analogous results. Indications of the existence of as 

 yet undiscovered compounds may be derived from a study of physical, 

 and particularly of electrical, changes. There appears to be sufficient 

 evidence of an oxide of hydrogen containing more oxygen than hydro- 

 gen dioxide, from a study of the electromotive force of a cell contain- 

 ing hydrogen dioxide; yet the higher oxide still awaits discovery. 



The interpretation of chemical change in the light of the ionic 

 theory may now be taken as an integral part of inorganic chemistry. 

 The ordinary reactions of qualitative and quantitative analysis are now 

 almost universally ascribed to the ions, not to the molecules. And the 

 study of the properties of most ions falls into the province of the in- 

 organic chemist. To take a familiar example: The precipitation of 

 hydroxides by means of ammonia-solution has long led to the hypothesis 

 that the solution contained ammonium hydroxide; and, indeed, the 

 teaching of the text-books and the labels on the bottles supported this 

 view. But we know now that a solution of ammonia in water is a 

 complex mixture of liquid ammonia and liquid water; of ammonium 

 hydroxide, NH 4 OH; and of ions of ammonium (NH 4 )', and hydroxyl 

 (OH)'. Its reactions, therefore, are those of such a complex mixture. 

 If brought into contact with a solution of some substance which will 

 withdraw the hydroxyl ions, converting them into water, or into some 

 non-ionized substance, they are replaced at the expense of the molecules 

 of non-ionized ammonium hydroxide; and these, when diminished in 

 amount, draw on the store of molecules of ammonia and water, which 

 combine, so as to maintain equilibrium, Now the investigation of such 



