36 Mr. T. Bayley on the Atomic Weights and the 



near tungsten and the platinum group, in the region of high 

 melting-point, low atomic volume, and coloured solutions. 



The facts known about the specific heat of uranium are, as 

 far as they go, compatible with the atomic weight 180. The 

 specific heat of metallic uranium has not been determined; but 

 the specific heat of the lowest oxide Ur 2 -0 3 (Ur=180) was 

 found by Regnault to be *0619. The product of the specific 

 heat of this oxide and the molecular weight is therefore 25*25; 

 and if we subtract from this the assumed specific heat 13'00 

 of the two atoms of uranium and divide the remainder by 3, 

 we arrive at a highly probable value for this heat of the atoms 

 of oxygen, viz. 4*08. The heat of the oxygen atoms is by a 

 similar process found to be 3*93 in sesquioxide of chromium, 

 4*12 in tungstic anhydride, and 4*04 in molybdic anhydride. 



The following table exhibits the formula? of the uranium 

 compounds, taking the atomic weight to be respectively 120, 

 180, 240:— 



Ur=120. Ur=180. 



UrCl 2 UrCl 3 



UrO Ur 2 3 



Ur 2 3 Ur 2 4 ,(Ur 2 5 ?) 



UrOCl Ur 2 3 Cl 3 



Ur 3 4 Ur0 2 



Ur 2 Ur0 3 



Uranium with atomic weight 180 may be regarded as the 

 atom-analogue of chromium, Ur 2 3 being the analogue of 

 Cr 2 3 , and Ur0 3 of Cr0 3 . The fact of the normal oxide 

 of uranium, Ur 2 5 , being a higher oxide than the normal 

 oxide of chromium, Cr 2 3 , is in accordance with the general 

 tendency of atomicity to increase with atomic weight. To 

 the foregoing it may be objected that tungsten has also claims 

 to be taken as the atom-analogue of chromium ; and many 

 arguments might be raised on behalf of each element. Whether 

 it is worth while to raise them is an open question. For it 

 it must be remembered that atom-analogy is likely to be most 

 perfect in twin cycles, and to be weaker when the cycles are 

 dissimilar. This is evidently so in the first four cycles: an 

 element in the first cycle resembles its atom-analogue in the 

 second more closely than its atom-analogue in the third or 

 fourth cycle; and an element in the third cycle resembles its 

 atom-analogue in the fourth cycle more closely than its atom- 

 analogue in the first or second. 



With increase in the complexity of the cycle comes the de- 

 velopment of new features and individualities ; thus the pro- 

 perty of forming coloured solutions appears for the first time 

 in the third cycle. The factor having the greatest influence 

 in determining the properties of an element appears to be 



Ur=240. 

 UrCl 4 

 UrO, 



Ur0 3 



Ur0 2 Cl 2 



Ur 3 8 



Ur0 4 





