610 



SCIENCE. 



[N. S. Vol. IX. No. 226. 



merits be arranged in the order of iuereas- 

 ing atomic weights there is a recurrence of 

 the properties of elements h)\ver in the 

 scale — in short, that these properties are 

 periodic functions of the atomic weights. 



The discovery of the new group of inert 

 gases, helium, neon, argon and xenon, with 

 perhaps krypton and metargon, has not 

 modified our idea of the Periodic Law essen- 

 tially. They appear to fit well into the sys- 

 tem, and it is now only remarkable that their 

 existence was not surmised by Mendelejefl', 

 who so successfully predicted several then- 

 unknown elements. Although the periodic 

 system is, even to-day, the object of attack 

 by a few chemists, who appear to be blinded 

 by its unquestioned defects to tlie obvious 

 truths which it expresses, it may be safely 

 said that the great central fact of the perio- 

 dicity in the properties of the elements is 

 just as firmly established as the law of gravi- 

 tation, and that, whatever modifications may 

 have to be made in the scheme as a whole, 

 this central fact will never be done away 

 with. The atomic theory may be supplanted 

 by something better, but its successor will 

 equally have to take account of the stoichi- 

 ometrical relations of the elements, which 

 are ba-ed not ontheorj', but on observation 

 pure and simple, and it is on these, and not 

 on the atomic theory, that the Periodic Law 

 is based. 



The Periodic Law is exerting a stimula- 

 ting influence on inorganic chemistiy in 

 various ways. It is leading to a more care- 

 ful study of all the elements, with the ob- 

 ject of discovering further analogies ; new 

 compounds are being prepared and old ones 

 studied better with this in view ; new kinds 

 of periodicity are being sought for in phys- 

 ical as well as in chemical properties. The 

 question of the nature of the rare earth 

 metals, the asteroids of the elementarj' 

 system, as Crookes calls them, is being at- 

 tacked with greater energy. Are these, of 

 which Ci-ookes claims there are thirty or 



perhaps sixty, capable of being fitted into 

 the system, as it now exists? Must we 

 modify it in order to take them in, or do 

 they represent certain exceptional phases 

 of the evolution of matter from the original 

 protyl, or different very stable modifica- 

 tions or allotropic forms of a few elements? 

 Do the blanks within the system represent 

 existing but as yet undiscovered elements? 

 Do some of them correspond to hypothe'tical 

 elements which for some unknown reason 

 are incapable of existence, like many or- 

 ganic compounds which are theoretically 

 jiossible, but which, if momentarily exist- 

 ing, lapse at once into other forms, or must 

 the scheme be so modified as to exclude 

 them ? These are some of the questions 

 raised by the Periodic Law which it be- 

 longs to the inorganic chemist to solve. 

 Most important of all is the question of the 

 cause of the periodicity. Before we can 

 hope to establish a mathematical and pos- 

 sibly a genetic relation between a series of 

 numbers, such as the atomic weights and 

 the chemical properties of the elements, we 

 must establish with greater accuracy than 

 heretofore the precise magnitude of these 

 numbers, and it is this that an ever increas- 

 ing number of atomic-weight chemists is 

 striving to do. The question of the unity 

 of matter is one to a solution of which we 

 are no nearer than ever, and the Periodic 

 Law, in its present form, does not afford a 

 proof or, I think, even a presumption in 

 favor of a genetic relation between the ele- 

 ments. It is quite conceivable that we may 

 have relations of properties without a com- 

 mon origin. With ever increasing accuracj'^, 

 we seem to be removing further and further 

 from the possibility of any hypothesis like 

 that of Prout. The electric furnace, with 

 its temperature of 3,500° C, gives not a sign 

 of the decomposition or transformation of 

 the elements. These questions and the 

 query why we know no elements below 

 hydrogen or above uranium, why the num- 



