APPENDIX H. 483 



years later the conception of the elements arose; it made chemistry what it 

 now is ; and yet we have advanced as little in our comprehension of simple 

 substances since the times of Lavoisier and Dalton as we have in our und*r- 

 istanding of gravitation. The periodic law of the elements is only twenty 

 years old; it is not surprising, therefore, that, knowing nothing about tho. 

 causes of gravitation and mass, or about the nature of the elements, we do 

 not comprehend the rationale of the periodic law. It is only by collecting 

 established laws that is, by working at the acquirement of truth that \\ o 

 can hope gradually to lift the veil which, conceals from us the causes of the 

 mysteries of Nature and to discover their mutual dependency. Like the 

 telescope and the microscope, laws founded on the basis of experiment are 

 the instruments and means of enlarging our mental horizon. 



In the remaining part of my communication I shall endeavour to show, 

 and as briefly as possible, in how far the periodic law contributes to enlarge 

 our range of vision. Before the promulgation of this law the chemical 

 elements were mere fragmentary, incidental facts in Nature ; there was no 

 special reason to expect the discovery of new elements, and the new ones 

 which were discovered from time to time appeared to be possessed of quite 

 novel properties. The law of periodicity first enabled us to perceive undis- 

 covered elements at a distance which formerly was inaccessible to chemical 

 vision ; and long ere they were discovered new elements appeared before oui" 

 eyes possessed of a number of well-defined properties. We jnow know three 

 cases of elements whose existence and properties were foreseen by the instru- 

 mentality of the periodic law. I need but mention the brilliant discovery of 

 ffaltwm, which proved to correspond to eka-aluminium of the periodic law, by 

 Lecoq de Boisbaudran ; of scandium, corresponding to ekaboron, by Nilson ; 

 .and of germanium, which proved to correspond in all respects to ekasilicon, 

 by Wlnkler. "When, in 1871, 1 described to the Russian Chemical Society 

 the properties, clearly defined by the ^eripdio law, which such elements 

 ought to possess, I never hoped that I should live to mention their discovery 

 to the Chemical Society of Great Britain as a confirmation of the exactitude 

 and the generality of the periodic law. Now that I have had the happiness 

 of doing so, I unhesitatingly say that, although greatly enlarging our vision, 

 even now the "periodic law needs further improvements in order that it may 

 become a trustworthy instrument in further discoveries. 9 



I will venture to allude to some other matters which chemistry has dis- 

 cemed by mjsaus of its new instrument, and which it could not have made 



I foresee 'some more new elements, but not w,ith the same certitude as before. I 

 shall give one example, and yet f do not see it quite distinctly. In the series which con- 

 tains Hg = 204, Pb = 206, and Bi ** 208, we can imagine the existence (at the place VI 11) 

 of an element analogous to tellurium, which we can describe as dvi-tellurium, Dt, having 

 fin atomic weight of 212, and the property of forming the oxide DtOj. If this element 

 really exists, it ought in the free state to be an easily fusible, crystalline, non- volatile 

 metal of. a grey colour, having a density pf about 9 - 8, capable of giving a dioxide, DtO?, 

 equally endowed with feeble acid and' basic properties. This dioxide must give on active 

 ! oxidation an unstable higher oxide, DtOj, which should resemble in its properties PbO 9 

 and Bi 2 5 . Dvi-tellurium hydride, if it be found to exist, will be a less stable compound 

 than even HjTe. The compounds of dvi-tellurium will be easily reduced, and it will form 

 characteristic defcute alloys with other metals. 



