264 PROCEEDINGS OP THE AMERICAN ACADEMY 



to cerous oxide by heating with the tungstate to a red heat for some 

 time. I may here state that a test for ceria more delicate than that 

 which I gave many years since (Pb0 2 and N0 3 H) is obtained 

 by employing the oxide of bismuth, Bi 2 4 , in place of plumbic 

 oxide. 



With these preliminaries I proceed to special methods of separating 

 the mixed oxides. A series of experiments was first made to determine 

 to what extent differentiation is effected by successive partial precipita- 

 tions by oxalic acid. The method is of course not new, but, so far as I 

 know, it has not been tested by quantitative analyses, and no attempt 

 has been made to determine the rate of change. The material used 

 in this case was a mixture of sulphates, the sulphate of neodymium 

 being present in largest quantity. Thoric and other oxides in less 

 quantity were also present. The material was obtained from Dr. 

 Shapleigh in the form of oxides. After careful purification the atomic 

 mass of the oxides was first determined : — 



(16) 0.5622 gr. gave 0.1715 gr. C 2 3 = 30.50 per cent. 



(17) 0.4782 gr. " 0.1458 gr. >' =30.50 " 



(18) 0.4355 gr. " 0.1326 gr. " = 30.47 " 



(19) 0.6100 gr. " 0.2778 gr. R 2 3 = 45.55 " 



(20) 0.6001 gr. " 0.3141 gr. " =45.50 



The analyses give as the .atomic mass 137.25. A portion of the 

 oxides was then converted into sulphate-, and the number of cubic 

 centimeters of a solution of oxalic acid required for complete precipi- 

 tation, determined by experiment with a sufficiently close approxima- 

 tion. A solution of the sulphates having a very fine rose-red color 

 was then precipitated in five successive additions of equal volumes of 

 a solution of oxalic acid. After each addition of the acid the resulting 

 oxalate was filtered off and washed. The washings were then added 

 to the filtrate. It will be seen that in this way the bulk of the solu- 

 tion increased before each precipitation after the first. The results 

 are as follows : — 



I. (21) 0.3126 gr. gave 0.0941 gr. C 2 3 = 30.52 per cent. 



(22) 0.3410 gr. " 0.1042 gr. " =30.54 



(23) 0.5773 gr. " 0.2820 gr. R 2 3 = 48.8 1 " 



(24) 0.5856 gr. " 0.2s.-,.') gr. " = 48.75 " 



Atomic mass 148.60. 



