218 



THE ATOMIC WEIGHTS. 



There are now before us twelve estimates for the molecular 

 weight of thoria. Two of these represent single experi- 

 ments, and have no probable error attached to them ; namely, 

 the one due to Hermann, and the one deduced from Berze- 

 lius' K2SO4 : ThOg ratio. A third value, from Delafon- 

 taine's sulphuric acid estimations, has so high a probable 

 error that it could be rejected without influencing the gene- 

 ral mean. These three values might all be excluded with- 

 out serious objection ; but it is perhaps better to arbitrarily 

 assign them equal weight, average them together, and give 

 their mean the same probable error as that which attaches 

 to Berzelius' BaSO^ : ThOa series. This mean is indicated 

 as "A" in the following combination : 



Value "A" ThOj = 263.623, 4= 



Berzelius. _ 

 Chydenius- 



-Sulphate 



" Acetate 



" Formate 



" Oxalate! 



Delafontaine — Higher hydrate . 

 " Lower " 



Cleve — Sulphate 



" Oxalate 



= 269.940, ±z 



— 268.584, rb 

 = 268.735, ± 

 = 272.586, rb 

 = 262.804, ztl 

 = 263.637, ± 

 = 266.025, zt 



— 265.380, ± 

 = 265.357, ± 



General mean. 



997 

 997 

 803 



805 

 877 



493 

 256 



123 

 104 



" =265.341,^.072 



Hence Th = 233.414, ± .0725 ; or, if = 16, Th = 

 233.951. 



These values vary from those derived from Cleve's experi- 

 ments alone only in the second decimal. 



GALLIUM. 



Gallium has been so recently discovered, and obtained in 

 such small quantities, that its atomic weight has not as yet 

 been determined with much precision. The following data 

 were fixed by the discoverer, Lecoq de Boisbaudran : 





* Journ. Chem. Soc, 1878, p. 646. 



