46 Journal of the Mitchell Society. [Marc/i 



Due to the great variation in values as g-iven by different 

 authorities and determined by different methods, and also the 

 just criticisms which have been lodg-ed against those methods 

 for other elements, it was deemed advisable to redetermine 

 the atomic weig-ht of thorium. We began by first investigat- 

 ing the methods formerly used and then attempted a new 

 method, with what success the sequel will show. In addition 

 to the criticism to which the various methods are subject, 

 recent investigations by Brauner 1 and Baskerville 2 , who have 

 been busied for years with the element, point to the complex- 

 ity of thorium. Moreover the radio-activity associated with 

 thorium is illy understood and appears not to belong- to pure 

 thorium compounds. 



Of methods used the value 232.6 depends on those of the oxal- 

 ate, formate, acetate and acetonyl-acetonate. With oxalate, 

 formate, acetate and acetonyl-acetate we have organic com- 

 pounds with a large number of atoms in the molecules and 

 varying number of molecules of water of crystallization pres- 

 ent. For instance, in the oxalate we have Th(C 2 4 ) 2 , 6H a O, 

 and the acetonyl-acetonate Th(C s H 7 2 ) 4 ; molecules with thir- 

 ty-one and fifty-seven atoms in them respectively. It is at once 

 evident that such complex molecules are not satisfactory for 

 atomic weig-ht determinations. 



It is upon the sulphate method chiefly that the atomic 

 weight of thorium depends, but the sulphate determinations 

 are open to serious objections. There is objection to using 

 any hydrated salts, because of the uncertainty of the compo- 

 sition. The anhydrous sulphate is objectional because of its 

 porous and deliquescent nature. Yet there are other difficul- 

 ties of much more importance than these. In most cases the 

 ratio between thorium oxide and sulphate was established by 

 incinerating- the sulphate. This is a difficult process and it 

 is extremely doubtful if all the sulphate can be decomposed, 

 as it forms a protective coating- of oxide. 



iLondon Ch. Soc. April, 10, 1901. 



2 J. American Ch. Soc., Vol. 23, No. 10., Oct,, 1901. 



