PRESENT PROBLEMS OF INORGANIC CHEMISTRY. 215 



ilioory may now 1)0 taken as an inton:ral part of inorfranir chemistry. 

 The ordinary reactions of (|ualilati"e and ([iiantitalive analysis are 

 now aliii>)st imi\-ei'sally a-;cril)ed lo the ions, not to the molecules. 

 And the study of the properties of most ions falls into the province 

 of the inoi'i>anic chemist. To take a familiar example: The precipi- 

 tation of hydroxides by means of annnonia solution has long led to 

 the liypothesis that the solution contained ammonium hydroxide, and, 

 indeed, the teachina' of the text-books and the labels (m the bottles 

 supported this view. But we know now that a solution of ammonia 

 in water is a complex mixture of liquid annnonia and liquid water; of 

 anunonium hydroxide, XII^OII ; and of ions of ammonium (NHJ', 

 and hydroxyl (OH)'. Its reactions, therefore, are those of such a 

 compli'x mixture. If brought into contact with a solution of some 

 substance which will withdraw the hydroxyl ions, converting them 

 into water, or into some nonionized substance, they are replaced at 

 the expense of the molecules of nonionized ammonium hydroxide; and 

 these, when diminished in amount, draw on the store of molecules of 

 annnonia and water, which combine, so as to maintain equilibrium. 

 Now, the investigation of such changes must belong to the domain of 

 inorganic chemistry. 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 investiga- 

 tions 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 

 a.re destined to become commercially important, it is impossible to 

 place the manufacturer on a sound commercial basis without ample 

 knowledge of physical methods and their application to the most 

 economical methods of accelerating certain reactions and retarding 

 otlu'rs, so as to obtain the largest yield of the required product at the 

 smallest cost of time, labor, and money. 



1 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 prol)lems are to be sought. But the develo])- 

 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 radio-activity and their bearing on the subject of my address. It 

 is difficult to gauge the relative importance of investigations in this 

 field; but 1 may be pardoned if I give a short account of what has 

 already been done and point out lines of investigation which ap])ear 

 to me likely to yield useful results. 

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



