14 P. T. Cleve, 



Mean of both determinations: 3.080. 

 Molecular vol. 114.3. 



Crystalline form monosj^mmetric. Crystals small, developed pa- 

 rallel to ooPoo. 



a : b : c = 0.341727 : 1 : 0.46170; ß = 84° 31' 56". 



Forms: ooP; ooPoo, Poo, 2Poo, ooPoo. (C.Morton). 



Selenate of didymium 



Di3Se04 + 5H,0. 



On evaporating the solution of oxide of didymium in selenic acid 

 on a water-bath, this salt is deposited in red four-sided prisms. 



0.8271 gram lost on heating to 240° 0.0896 gram HgO and gave 

 on ignition to a white heat 0.3432 gram DijOj. 



1.5185 gram gave 0.1651 gram H2O and 0.6333 gram DiaOj. 



3.7442 gram was heated to 230° and gave 0.4168 gran^ H2O. 



In percent: Calc 



Di^Os 41.49 41.71 — 332 41.34 



SeOa (47.68) (47.42) — 381 47.45 



H2O 10.83 10.87 11.13 90 11.21 



100.00 100.00 803 100.00 



Spec. grav. of the crystallised salt: 



1.9203 gram, crystals t° 18".3 spec. Grav. 3.685 

 1.4336 » » t° 15° » » 3.677 



Mean of both determinations: 3.681. 

 Molec. vol.: 218.1. 



By evaporation of the solution at ordinary temperature rounded 

 masses of very fine needles are obtained, which could not be perfectly 

 freed from the mother-liquor. According to my former researches this 

 salt seems to contain IOH2O. I have not been able to get a selenate 

 with 8H2O from the pure oxid of didymium. 



