266 INORGANIC CHEMISTRY 



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 

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

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

 thesis 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 mole- 

 cules of non-ionized ammonium hydroxide; and these, when dimin- 

 ished in amount, draw on the store of molecules of ammonia and 

 water, which combine, so as to maintain equilibrium. Now the investi- 

 gation of such changes must belong to the domain of inorganic chem- 

 istry. It is true that the methods of investigation are borrowed from 

 the physical chemist; but the products lie in the province of the 

 inorganic chemist. Indeed, the different departments of chemistry 

 are so interlaced that it is impossible to pursue investigations in any 

 one branch without borrowing methods from the others; and the 

 inorganic chemist must be familiar with all chemistry, if he is to 

 make notable progress in his own branch of the subject. And if the 

 substances and processes investigated by the inorganic chemist are 

 destined to become commercially important, it is impossible to place 

 the manufacture on a sound commercial basis without ample know- 

 ledge of physical methods, and their application to the most econom- 

 ical methods of accelerating certain reactions and retarding others, so 

 as to obtain the largest yield of the required product at the smallest 

 cost of time, labor, and money. 



I have endeavored to sketch some of the aspects of inorganic chem- 

 istry with a view to suggesting problems for solution, or at least the 

 directions in which such problems are to be sought. But the develop- 

 ments of recent years have been so astonishing and so unexpected, 

 that I should fail in my duty were I not to allude to the phenomena of 

 radioactivity, and their bearing on the subject of my address. It is 

 difficult to gauge the relative importance of investigations in this 

 field; but I may be pardoned if I give a short account of what has 

 already been done, and point out lines of investigation which appear 

 to me likely to yield useful results. 



The wonderful discovery of radium by Madame Curie, the prepara- 



