ORIGIN OF ELEMENTARY SUBSTANCES. 137 



U, sp. gr. = 18*3. From a study of the chemical combina- 

 tions of this element^ Mendeleef has assigned to it the 

 atomic weight of 240"^, or double the number formerly re- 

 ceived, and which number I have adopted. The admission 

 of this high atomic weight, however, separates uranium 

 from chromium, molybdenum, and tungsten, with which it 

 hasbeen classified, as there are no elements of approximately 

 the same high specific gravities as tungsten= 18*26, and 

 uranium = 1 8*3, correlated with so great a difference of 

 atomic weights as U = 240, and W = 1 84, From the fact 

 that the highest places in all the series, except that in 

 H4W, are filled up with their highest members, and that 

 uranium is generally found in combination with the 

 mineral species yttrotantalite, fergusonite, polykrase, pyro- 

 chlore, pyrrhite, containing elements of the series H3W on 

 the one side, and in combination with minerals containing 

 elements of the series H5% on the other, I have classified 

 uranium as the highest form of H^n. The two lower 

 forms of H4W, as will be seen from the table, are missing f ; 

 but, assuming that titanium is the highest member in a 

 triad with the missing elements, the atomic weights of 

 the latter are 16 and 32, isomeric with oxygen and sulphur. 

 It may, however, be surmised that no elements now exist to 

 fill the gaps in the series, as they may have become extinct 

 by absorption into titanium and its analogues, or by trans- 

 formation into the negative forms of H2w. 



The elements which I have classified as forms of H6« 



* Ann. Chem. Pharm. Suppl. -viii. pp. 178-184. 



t Prof. Winkler of Freiberg has recently discovered a new eleaient 

 which he has named "Germanium" (symbol Ge). ('Nature,' March 4, 

 1886 ; ' Berichte' of the Berlin Chemical Society, No. 3). Germanium was 

 first considered by Winkler to belong to the antimony and bismuth group ; 

 but the subsequent determinations of its specific gravity 5*469, and atomic 

 weight 7275, place the new element in the vacant position x=-jz in the 

 series Il4«, and in the group of titanium and tin. — H. W., 1886. 



