12 P. T. Cleve, 



Sulphate of didymium. 



1. Anhydrous salt, D'^SSO^. 



Spec. Grav: 



1.6536 gram, temp. 18°.3 sp. Grav. 3.672 

 1.8473 » » » » » 3.662 



/ 



Mean of both determinations: 3.667. 

 572 

 3.667 



572 

 Molecular volume: = 156. 



2. Di23SO, + 8H20. 



Spec. Grav: 



2.1520 gram temp. 16'' sp. Gr. 2.831 



2.8886 » » 14°.8 » » 2.827 



2.9228 » » 16°.2 » » 2.828 



Mean of the three determinations: 2.829. 



Molecular volume: 253.1. 



3. Di23S04 + 5H2O. This sulphate is obtained by evaporation 

 of solutions at nearly 100° and separates in red needles, which very 

 rapidly take up water at the ordinary temperature, so that it is extre- 

 mely difficult to get it with exactly 5H2O. This is certainly the reason 

 why Marignac assignes to it 6H2O. 



1.1775 gram lost on heating O.1688 gram H2O. 



In percent: 14.34. Calc: 13.60. 



Six mol. H2O corresponds to 15.88 percent. 



Sulphate of didymium and potassium 



2Di23S04 + 9K2SO4 + 3H2O. 



On adding to a cold solution of the acetate of didymium an 

 excess of sulphate of potassium, a red, scarcely crystalline, heavy pow- 

 der separates. It was pressed between filter-paper and analysed. 



1.3974 gram lost on heating 0.0267 gram H2O and gave 0.3408 

 gram DijOg and 0.7905 gram K2SO4. 



