144 Prof. H. Rose on the Composition of Samarskite. 



When, therefore, the composition of minerals containing tan- 

 talum, and especially niobium, has not been thoroughly ascer- 

 tained by experiment, it is as well to give up altogether the 

 decomposition by bisulphate of potash, and to effect the decom- 

 position by potash. By this means the zirconia and thorina, as 

 also titanic acid and oxide of cerium, which are insoluble in an 

 excess of potash, may be separated from the acids of tantalum, 

 and especially of niobium, which dissolve as potash salts, are 

 readily soluble in an excess of potash, and can only be contami- 

 nated with tungstic acid and stannic acid, from which they are 

 easily separated, and also by silica. The decomposition is best 

 effected by fusion with hydrate of potash. As, however, this 

 must take place in a silver crucible, the employment of which is 

 attended by many inconveniences, and by which a contami- 

 nation of the fused mass with oxide of silver cannot be avoided, 

 it is more advisable to employ carbonate of potash, with which 

 the mineral may be fused in the platinum crucible. If the 

 fusion be effected at first over a lamp, and then only for a short 

 time with a small blast, the decomposition is perfect. 



I had a particular interest in establishing the correct compo- 

 sition of Samarskite, as I had been furnished, by the liberality of 

 M. von Samarski, with a very large quantity of this rare mineral 

 for investigation. The mineral also is interesting in many re- 

 spects. As the analyses of Samarskite made in my laboratory 

 differ so considerably from each other, I induced M. Finkener to 

 repeat the analysis of the mineral; and only by his invincible 

 perseverance has it been possible, notwithstanding the partly 

 imperfect methods of separation, to arrive at satisfactory results, 

 and detect substances previously overlooked. 



After the decomposition of the mineral by carbonate of potash, 

 and the treatment of the fused mass with water, the hypo- 

 niobic acid was precipitated from the solution by sulphuric acid, 

 and separated from small quantities of tungstic and stannic 

 acids. Small quantities of peroxide of copper were precipitated 

 from the solution by sulphuretted hydrogen ; the solution was 

 then slightly supersaturated with ammonia, and the bases, except 

 lime and magnesia, were thrown down by sulphide of ammo- 

 nium, partly as oxides, partly as sulphides. From the solution 

 of these in hydrochloric acid, after saturation with ammonia, 

 the oxides were again precipitated by carbonate of ammonia and 

 sulphide of ammonium, and only oxide of uranium was dissolved; 

 this, as appeared on examination, contained zirconia. The sepa- 

 ration of these is attended with great difficulty, and could only 

 be effected by neutralizing the solution in sulphuric acid by 

 ammonia and boiling it, when zirconia, containing, however, 

 oxide of uranium, was precipitated, and the greater part of the 



