486 PEINCIPLES Off CHEMISTRY 



The expectations of the periodic law 8 have been confirmed, first, by n,e> 

 determinations of the atomic weight of ptatvmm (by Seubert, Dittmar, and 

 W Arthur, which proved to be near. to 196 (taking = 16, as proposed by 

 Marignac, Brauner, and others) j secondly, by Seubert having proved that 

 the atomic weight of osmwm is really lower than that of platinum, being 

 near to 191; and thirdly, by the investigations of Krtiss, Thorpe and 

 Laurie, proving that the atomic weight of gold exceeds that of platinum, 

 and approximates to 197. The. atomic weights .which were thus found to 

 require correction were precisely those, which the periodic law had indicated 

 as affected with errors ;. and it has been proved/ therefore, that the periodic 

 law affords a means of testing experimental results. If we succeed in dis- 

 covering the exact character of the periodic relationships between the 

 increments in atomic weights of allied elements discussed by Eidberg in 

 1885, and again by Bazaroff in 1887, we may expect that our instrument 

 will give us the means of still more closely controlling .the experimental data, 

 relating to atomic weights. 



Let me next call to mind that, while disclosing the variation of chemical 

 properties, 9 the periodic law has also enabled us to systematically discuss 

 many of the physical properties of elementary bodies, and to show that these 

 properties are also subject to the law of periodicity. At the Moscow Congress 

 of Bussian Naturalists in August, 1869, I dwelt upon the relations which 

 existed between density and the atomic weight of the elements. The follow- 

 ing year Professor Lothar Meyer, in his well-known paper, 10 studied the 

 same subject in more detail, and thus contributed to spread information 

 about the periodic law. Later on, Carnelley, Laurie, L. Meyer, Roberts* 

 Austen, and several others applied the periodic system to represent the order 

 in the changes of the magnetic properties of the elements, their melting 

 points, the heats of formation of their haloid compounds, and even of such 

 mechanical properties as the co-efficient of elasticity, the breaking stress, &c., 

 Ac. These deductions, which have received further support in the discovery 

 of new elements endowed not only with chemical but even with physical 

 properties, which were foreseen by the law of periodicity, are well known ; 

 eo I need not dwell upon the subject, and may pass to the consideration of 

 oxides. 11 



8 I pointed them out in the Liebig's Annalen, Supplement Band* viii. 1871, p. 211. 



9 Thus, in the typical small period of 



Li,Be,B,C,N,0,F, 



we see at once the progression from the alkali metals to the acid non-metals, such as 

 are the halogens. 



LieUg's Annalen, Supplement Band., vii 1870. 



11 A distinct periodicity can also be discovered in the spectra of the elements. Thua 

 the researches of Hartley, Ciamician, and others have disclosed, first, the homology 

 of the spectra of analogous elements: secondly, that the alkali metals have simpler 

 epectra than the metals of the following groups; and thirdly, that there is a certain like- 

 ness between the complicated spectra of manganese and iron on the one hand, and the 

 no less complicated spectra of chlorine and bromine on the other hand, and their likeness 

 corresponds to the degree of analogy between those elements which is indicated by the> 

 periodic law. 



