148 Scientific Intelligence. 



same value (e. g., platinum, iridium, osmium) or which in- 

 crease regularly (e. g., potassium, rubidium, caesium); (3) the ar- 

 rangement of the elements in the order of their atomic masses 

 corresponds to their so-called valencies as well as, to some 

 extent, to their distinctive chemical properties ; (4) the elements 

 which are the most widely diffused have small atomic masses; 

 (5) the magnitude of the atomic mass determines the character of 

 the element just as the magnitude of the molecule determines the 

 character of a compound body; (6) we must expect the discovery 

 of many yet unknown elements — for example,. elements analogous 

 to aluminum and silicon, whose atomic mass would be between 

 65 and 75 ; (7) the atomic mass of an element may sometimes be 

 amended by a knowledge of those of the contiguous elements ; 

 i. e., the atomic mass of tellurium must be between 123 and 126 

 and cannot be 128; and (8) certain characteristic properties of the 

 elements can be foretold from their atomic masses. And in 1889, 

 twenty years afterwards these conclusions may still be considered 

 as expressing the essence of the now well known periodic law. 

 Three sets of data had contributed to make the discovery of this 

 law possible. In the first place the true conception of an atom 

 had been arrived at and real atomic masses had been reached. 

 The relation between K 39 and Ca 20, between Rb 85 and Sr 

 43-5, between Cs 133 and Ba 68*5 fails entirely to show the con- 

 secutiveness in atomic mass, which becomes so apparent when Ca 

 is 40, Sr is 87 and Ba is 137. In the second place it had already 

 become, evident that the relations between the atomic masses of 

 analogous elements were governed by some general and simple 

 laws ; in proof of which the classifications of Cooke, Dumas, 

 Strecker and others may be mentioned. Among these he includes 

 Newland's "Law of Octaves;" which although suggestive, in- 

 cluded elements having no apparent connection with each other 

 in the same octave, and which contained occasionally ten ele- 

 ments in the octave instead of eight. The third circumstance 

 favoring the discovery of the law of periodicity was the accumu- 

 lation of new information respecting the rarer elements, dis- 

 closing their many-sided relations to the other elements and 

 to each other ; among specially important researches being 

 those of Marignac on columbium and of Roscoe on vana- 

 dium. When the striking analogies between vanadium and phos- 

 phorus on the one hand and between vanadium and chromium on 

 the other had become apparent, and when V 51 had been com- 

 pared with Cr 52, Cb 94 with Mo 96 and Ta 192 with W 194, or 

 P 31 with S 32, As 75 with Se 79 and Sb 120 with Te 125, there 

 remained but a step to the discovery of the law of periodicity. 

 Mendeleeff then passes to an attempt to answer the question 

 wherein lies the secret of the special importance of the periodic 

 law, which has already given to chemistry unexpected aid and 

 which promises to be far more fruitful and to impress upon sev- 

 eral branches of chemical research a peculiar and original stamp. 

 As soon as the law appeared, it demanded a revision of many 



