18 P. T. Cleve, 



In percent: 



C a 1 c 



SDi.Os 50.40 996 49.55 



SSeOa 43.54 888 44.18 



7H2O (6.06) 126 6.27 



100.00 2010 100.00 



A precipitate, obtained from acetate of didymiuni and the sele- 

 nate of ammonium, gave by analysis: 



0.3759 gram, pressed between filter-paper, gave on ignition O.166O 

 gram DigOg. 



0.4068 gram gave O.1115 gram Se. 



Cale 



SDi^Oa 44.16 996 ÏIos 



8Se02 39.72 888 39.26 



2IH2O (16.12) 378 16.71 



100.00 2262 100.00 



It is really remarkable that the ratio between DioOg and Se02 is 

 so constant in both these preparations. Mr. Nilson observed the same 

 ratio and assigned the formula 3Di2 03, 8Se02, 28H2O to the precipitate 

 obtained by the first of the above methods. The basic selenite of sa- 

 marium, prepared in precisely the same manner gave a perfectly ana- 

 logous formula viz. 3Sm203, 8SeO,, TH^O (dried at 100°). 



2. Acid salt. DiaOa, 4Se02 + öHjO. By adding an excess of 

 selenious acid to the solution of the acetate of didymium a lilac-colou- 

 red crystalline precipitate is thrown down. The salt loses at 105". 4.68 

 percent HjO or 2 mol. (cale 4.14). 



0.5945 gram gave by ignition 0.2296 gram Di2 03. 



0.8247 gram gave 0.2970 gram Se and 0.3165 gram DigOg. 



0.7205 gram gave 0.2587 gram Se and 0.2758 gram DigOj. 



In percent: _, , 



^ Calc 



Di^Os 38.62 38.38 38.28 332 38.34 



SeO, — 50.60 50.45 444 51.27 



H2O — (11.02) (11.27) 90 10.39 



866 100.00 



