Chemical and Physical Properties of Elements. 35 



a, axb, axlr, ax b 3 , a x 6 4 , 

 where a = 10 and & = l - 67, 

 = lo # 



The increments are 



10, 16-5, 27-9, 46-6, 77-8; 

 and the corresponding atomic weights, 



11, 27-5, 55-4, 102-0, 179-8. 



Enough has now been said to indicate the close connexion 

 between the physical properties of elements and the periodic 

 variation; and it has been shown that in the majority of in- 

 stances the density, the melting-point, (the expansion for heat.) 

 the magnetism, and the behaviour of the solution to trans- 

 mitted light have definite relations to the atomic weight. 

 This being so, and it being well known that certain other 

 physical properties of substances closely associated with atomic 

 weight (for instance, vapour-density, isomorphism, and spe- 

 cific heat) are extensively used to decide which of the powers 

 of the equivalent of an element is the weight of its atom, it 

 may be worth while to ask whether the general physical pro- 

 perties of an element, and not only certain isolated ones, should 

 not be called in to decide the all-important question of atomic 

 weight. A crucial test of the value of this method is afforded 

 by uranium. This element has the equivalent 60: and its 

 atomic weight was, until lately, taken as 120. But Mendele- 

 jeff, for reasons which he states fully, has assigned to it the 

 atomic weight 210. Our knowledge of uranium and its com- 

 pounds is largely due to Peligot ; and he and others have 

 established the following facts regarding it: — 

 It has high density, 18*4. 

 It melts only at the heat of a wind-furnace. 

 It forms strongly coloured solutions, and, according to 

 Yerdet, it is magnetic. 



If the atomic weight of uranium is 120, it comes where 

 there is no place for it, between tin and antimony; for its 

 volume is 6~d, while the volume of tin is 16 - 1 and that of 

 antimony 18*2; it has high melting-point, while they melt at 

 comparatively low temperatures; and it forms coloured solu- 

 tions, while their solutions are colourless. In the same way, 

 if the atomic weight of uranium is 240, the volume is 13 in- 

 stead of about 30; and it occupies the region of the fifth cycle 

 beyond bismuth, where, unless all analogy fails, we should 

 not expect to find a metal with very high melting-point and 

 coloured solutions. But if the atomic weight of uranium be 

 180, it conforms with the known properties of the element. 

 The atomic volume is then 10. and the element takes its place 

 D2 



