16 P. T. Cleve, 



Mean of both determinations: 3.176. 

 Molecular volume: 175.4. 



Anhydrous salt: 



1.0725 gram t.° 13° sp. Gr. 3.839. 



Molec. volume: 121.7- 



Crystalline form monosymmetric ; beautiful crystals, protracted 

 parallel to the orthodiagonal. 



a : b : c = 0.84906 : 1 : 1.12531 

 ß = 88°.2i'. 



Planes : oo P; oo P oo ; — P oo ; + | P oo ; P oo ; 2 P oo ; oP. (C. Morton). ' 



Selenate of didymium and ammonium 



DiNH4 2Se04 + 5H,0. 



It crystallises, as does the analogous potassium-salt, in large and 

 well formed red prisms which are easily soluble in water. 



0.8745 gram was treated as the potassium-salt and gave 0.2572 

 gram Se and 0.2729 gram Di^Os. 



0.9106 gram gave 0.2678 gram Se and 0.2843 gram DiaOs- 



In percent: ^ , 



^ Calc 



Di,03 31.21 31.22 166 30.97 



(NH,)20 — — 26 — _ 



SeOs 47.28 47.28 254 47..39 



H^O — — 90 — 



536 

 Spec. Grav: 



2.0102 gram, crystals, t." 15" sp. Gr. 2.957 



1.4062 » » » » » » 2.961 



Mean of both determinations : 2.959. 

 Molecular volume: 181.1. 



Crystalline form rhombic; well formed crystals, protracted parallel 

 to the vertical axis. 



