PRESENT PROBLEMS OF INORGANIC CHEMISTRY. 215 



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

 The ordinary reactions^of (fualitative and (inantitatiye analysis are 

 DOW almost nniyers^lly ascribed to the ions, not to the molecules. 

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

 of tlie incn-ganic chenust. To take a familiar example: The precipi- 

 tation of hydroxides by means of annnonia 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 yiew. l)Ut W(> know now that a solution of ammonia 

 in water is a complex mixture of licjuid auunonia and liquid w;iter; of 

 ammonium hydroxide, NH^OH; and of ions of aunnoniiun (NHJ', 

 and hyclroxyl (OH)'. Its reactions, therefoi-e, ai'e tlu)se of such a 

 complex mixture. If l)rought into contact witli a solution of some 

 substance which will withdraw the hydi'oxyl ions, converting them 

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

 the expense of the molecules of nonionized aunnonium 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 inyestigation of such changes nnist belong to the domain of 

 inorganic chemistry. It is true that the methods of inyestigation 

 are borrowed from the physical chenust; but the products lie in the 

 proyince of the inorganic chemist. Indeed, the different departments 

 of chemistry are so interlaced that it is imjjossible to pursue investiga- 

 tions in any one branch without boi'rowing methods fi'om the others; 

 and the inorganic chemist nnist 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 l)y the inorganic chemist 

 are destined to l)ecome connnercially important, it is impossible to 

 place the manufacturer on a sound commercial basis without ample 

 knowdedge of physical methods and their application to the most 

 economical 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 endeayored to sketch some of the aspects of inorganic chem- 

 istry with a view to suggesting pntblems 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 radio-activity and their bearing on the sul)ject of my address. It 

 is difficult to gauge the relative inq)ortance of investigations in (his 

 field; but I may be pardoned if I give a shoi-t 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- 



