26 SIR WILLIAM CROOKES ON SCANDIUM. 



SCANDIUM AND POTASSIUM DOUBLE SULPHATE, 

 3K 2 S0 4 ,Sc 3 (S0 4 ) 3 . 



The behaviour of the double sulphates of potassium and the rare-earth metals is 

 usually considered to govern their position in the broad groups into which they are 

 divided. If the double sulphate is insoluble in a saturated solution of potassium 

 sulphate the earth is supposed to belong to the cerium group, while if the double 

 sulphate is soluble the earth is said to be one of the yttrium group. According to 

 CLBVE (' Comptes Rendus,' vol. Ixxxix., p. 419, August 18, 1879): "Potassium 

 sulphate in concentrated solution gives rise to the separation of a double salt, a 

 crystalline powder, soluble in a saturated solution of potassium sulphate." CLEVE 

 gives the composition of the double salt as Sc 2 O 3 ,3SO 3 +2K 2 O,SO 3 . On the other 

 hand, NlLSON says (' Comptes Rendus,' vol. xci., p. 118, July 12, 1880) : " Scandium 

 sulphate in a saturated solution of potassium sulphate gives a double salt, completely 

 insoluble. ... It dissolves with difficulty in water, even boiling, and not at all 

 in a saturated solution of potassium sulphate. . . . The composition of the double 

 salt, 3K 2 2 SO 2 + Sc 2 3SO a , shows that scandium belongs to the group of gadolinite 

 and cerite metals, all these metals giving salts of the same typical composition." 



In .view of these diametrically opposite statements I have taken especial pains to 

 ascertain the true behaviour 1 of the double salt. 



17 '7 17 grs. of re-crystallised scandium sulphate, found by analysis to be pure, were 

 dissolved in water in a flask. The calculated quantity of potassium sulphate to unite 

 with the 17'717 grs., and to make a saturated solution in the water added, was then 

 weighed out, and 5 per cent, additional potassium sulphate was added to ensure 

 complete saturation. This was dissolved in boiling water, put into the flask con- 

 taining the scandium sulphate, and water up to 250 cc. was added. The flask was 

 securely corked, and put into a mechanical agitator, where it was shaken continuously 

 for twenty-five hours. At first, when the two salts were mixed, no precipitation 

 of double salt was visible, but after a short time there appeared a fine granular 

 precipitate, which gradually increased as the shaking proceeded. 



At the end of twenty-five hours the precipitated double sulphate was filtered 

 off and washed with 100 cc. of cold saturated solution of potassium sulphate. The 

 filtrate was heated, ammonia added, and the whole well boiled. A very slight 

 precipitate of scandia came down which, when filtered, washed, and ignited, weighed 

 0-414 gr., equivalent to T473 grs. of scandium sulphate in solution, the rest of the 

 sulphate being in the insoluble precipitate. It therefore follows that for every 

 100 parts of the double sulphate 8'32 per cent, are soluble and 91'68 per cent, are 

 insoluble in the amount of saturated solution of potassium sulphate employed. 



The insoluble double salt was washed with boiling water to remove the little excess 

 of potassium sulphate, until its bulk was reduced about one-half. It was then dried 

 and analysed. 



