21 



0.8456 gram, t" 15* sp. Gr. 2.850 

 0.5142 » » » )) » 2.872 



Mean of both determinations: 2.861. 

 Molecular volume: 212.5. 



Crystalline form. The carbonate is, according to the determina- 

 tions of Mr. C. Morton, rhombic and isomorphous with lanthanite. 



a : b : c = 0.95617 : 1 : c. 



Planes: oP; 00 P; c» P 00. 



The plane of the optical axes is, as on the lanthanite, parallel 

 to 00 P 00. One of the bisectrices of the optical axes goes out on the 

 basic plane. 



Carbonate of didymium and potassium 



DiK2C0; +6H,0. 



On mixing a solution of acetate of didymium with an excess of 

 bicarbonate of -potassium a gelatinous and bulky precipitate was thrown 

 down. It was left in the liquid for some time and had then changed 

 into brillant lilac-coloured needles. The salt was pressed between filter- 

 paper and subjected to the following analyses: 



0.7721 gram lost by 110" 0.2018 gram H^O. 



0.8372 gram gave 0.3376 gram DigOs and 0.1597 gram KCl. 



0.8632 gram gave 0.3457 gram DiaOg and 0.1653 gram KCl. 



