238 THE ATOMIC WEIGHTS. 



Hermann's * determination of the atomic weight of didy- 

 mium rests on a single experiment with the sulphate. By- 

 precipitation as oxalate and subsequent ignition, he found 

 that this salt yielded 58.14 per cent, of DigOg. 



Zschieschef also analyzed didymium sulphate, which he 

 dehydrated at 230°, and afterwards converted into oxide by 

 calcination. I give his percentages, and also, in a fourth 

 column, the percentage of oxide from the anhydrous sul- 

 phate as deduced from his figures : 



The salt used in the first experiment probably contained 

 lanthanum. Rejecting this, the mean of the figures remain- 

 ing in the fourth column is 57.926, ± .094. Hence Di = 

 141.007. 



Erk,| to whom reference has alread}' been made, estimated 

 didymium in the sulphate by precipitation as oxalate and 

 calcination to oxide : 



D,\{SO,\ Di^O^. Per cent. Di^O.,. 



.556 grm. .323 grm. 58.094 



.674 " .3915 " 58.087 



Hermann's single result for this percentage, 58.14, agrees 

 more nearly with Erk's series than with any other. It may 

 therefore be averaged in with Erk's two experiments, giving 

 a mean of 58.107, =!= .0112. Erk also obtained from .7065 

 grm. of sulphate .859 grm. BaSO^. This experiment has 

 already been averaged with Marignac's earlier results. 



The latest determinations of the atomic weight of didy- 

 mium were published by Cleve 1| in 1874. Strongly calcined 



* Journ. fiir Prakt. Chem., 82, 367. 1861. 



f Joum. fur Prakt. Chem., 107, 74. 



J Jenaisches' Zeitschrift, 6, 306. 1871. 



II K. Svenska Vet. Akad. Handlingar, Bd. 2, No. 8. These figures were kindly 

 transcribed for me by Professor Delafontaine of Chicago, as I had not access ta 

 a copy of the original memoir. 



