150 Scientific Intelligence. 



termediate elements between silver which gives AgCl and cad- 

 mium which gives CdCl 2 , but according to the very essence of the 

 periodic law there can be none; in fact a uniform curve would be 

 inapplicable in such a case, as it would lead us to expect elements 

 possessed of special properties at any point of the curve. The 

 periods of the elements have thus a character very different from 

 those which are so simply represented by geometers. They cor- 

 respond to points, to numbers, to sudden changes of the masses and 

 not to a continuous evolution. In these sudden changes destitute 

 of intermediate steps or positions, in the absence of elements 

 intermediate between say silver and cadmium or aluminum and 

 silicon, we must recognize a problem to which no direct applica- 

 tion of the analysis of the infinitely small can be made. There- 

 fore neither the trigonometrical functions proposed by Ridberg and 

 Flavitzky nor the pendulum-oscillations suggested by Crookes, 

 nor the cubical curves of the Rev. Mr. Haughton, which have 

 been proposed for expressing the periodic law, can, from the 

 nature of the case, represent the periods of the chemical ele- 

 ments." 



With reference to the bearing of the periodic law on the ques- 

 tion of a primary matter, Mendeleeff says : The periodic law based 

 as it is on the solid and wholesome ground of experimental re- 

 search, has been evolved independently of any conception as to 

 the nature of the elements ; it does not in the least originate in 

 the idea of a unique matter; and it has no historical connection 

 with that relic of the torments of classical thought, and therefore 

 it affords no more indication of the unity of matter or of the com- 

 pound character of our elements than the law of Avogadro* or the 

 law of specific heats or even the conclusions of spectrum analysis. 

 None of the advocates of unique matter have ever tried to ex- 

 plain the law from the standpoint of ideas taken from a remote 

 antiquity when it was found convenient to admit the existence of 

 many gods — and of a unique matter." 



In concluding, the lecture discusses the enlargement of the 

 range of vision by the periodic law. For the first time it enabled 

 us to perceive undiscovered elements at a distance hitherto unac- 

 cessible to chemical vision and to define their properties ; as is 

 seen in gallium, scandium, and germanium. A fourth element 

 he now foresees analogous to tellurium, which he calls dui-teilu- 

 rium, Dt, having an atomic mass of 212 and forming an oxide 

 Dt0 3 . It is an easilv fusible crystalline non-volatile metal of a 

 gray color, having a density of about 9*3, and giving an oxide 

 Dt0 2 equally endowed with feeble acid and basic properties. 

 On active oxidation it gives Dt0 3 which resembles PbO; and 

 Bi a 6 and is unstable. The hydride will be less stable than H 2 Te. 

 Its compounds will be easily reduced and it will form characteris- 

 tic alloys. Attention is then called to the way in which the 

 periodic law has compelled a modification of both atomic masses 

 and valencies, as in the cases of indium, cerium, yttrium, beryl- 

 lium, thorium and uranium, and has detected errors in atomic 



