DiDYMlUM. 17 



a : b : C = 0.88784 : 1 : 0.7111. 

 Planes : cx3P;ooPoo;ooPoo;P oo. 



Optical positive. The plane of the optic axes parallel to oo P oo. 

 (C Morton). 



Sulphite of didymium 



Di^SSOs + GHaO (or 2H,0 dried at 100"). 



Oxide of didymium is easily soluble in a solution of sulphurous 

 acid in water. If the solution be heated on the water-bath, a volumi- 

 nous precipitate of the sulphite is thrown down. Prior to analysis the 

 salt was pressed between filter-paper. 



0.3228 gram lost by heating to 100° 0.0384 gram and gave 0.2931 

 gram Di^SSOi. 



0.3579 gram lost by 100'' 0.0433 gram HjO and gave 0.3232 gram 

 Di^SSO^. 



In percent: 



^ Calc 



Di.Os 52.70 52.41 332 52.53 



80, — — 192 — 



HjO at 100» . . 11.90 12.10 72 11.39 



2HoO — — 36 — 



632 



Selenites of didymium. 



1. Basic salt. SDi^O,, 8Se02 + 21H20 (or 7H2O dried at 100°). 



By mixing the solutions of neutral selenite of sodium and sul- 

 phate of didymium a very voluminous and gelatinous precipitate is thrown 

 down, resembling the hydroxide of didymium. It was dried at 100°. 



0.9488 gram, dissolved in HCl and precipitated with SO2, gave 

 0.2940 gram Se, and from the filtrate 0.4782 gram DigO,, was precipita- 

 ted as oxalate. 



Nova Acta Reg. Soc. Sc Ups. Ser. III. 3 



