536 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



reproduced here. L. Ilormann ' also has studied the subject, and states 

 that the old erbia is separable into two earths, one giving red and the 

 other yellow salts. 



More recent dctenninations of the atomic weight of erbium are as 

 follows. First, two unimportant analyses made by Brill ^ with the aid 

 of the microbalance : 



E>\(.80,)s. E7\03. Per cent. Er^Oi. 



92.35 56.55 61.234 



36.75 22.68 61.496 



Mean, 61.365, ± .0873 



Hence Er= 166.76. 



Under the name " neo-erbium "' Hof maun and Burger ^ describe care- 

 fully purified material, which gave a sharp and distinct spectrum. Four 

 syntheses of the sulphate gave the subjoined figures : 



0031 



Hence Er = 167.40. 



It is not necessary to combine these data. The latest, by Hofmann 

 and Burger, is the most probable, and should be accepted. 



The atomic weight of thulium has not yet been carefully determined. 

 Cleve * assigned to it the atomic weight 170.7, but without details as to 

 weighings. According to Urbain,^ the atomic weight is below 168.5. 

 Urbain " also states that the value for holmium is near 140. 



^ Dissertation, Technische Hochschule, Miinclien. 19C6. 

 = Zeitsch. anorg. Chem., 47, 464. 1905. 

 ^ Ber. Deutsch. chem. Ges., 41, 308. 1908. 

 •• Compt. Rend., 91, 329. 1880. 



' Compt. Rend., 145, 759. 1907. Aecdidinsr to Aiier von Welsbach (Anzeiger Wien. .\kad. , 45, 

 529), th\iliuni is really complex. The atdniic wciKlit a~sifrned to it has little significance. 

 » Bull. Soc. Chim. (3), 33, 403. 1905. 



