W. P. Ileadden — Colmnbite and Tantalite. 93 



out with dilute sulphuric acid, the mixed acids were thor- 

 oughly washed aud dissolved in hydrofluoric acid, the solution 

 after the addition of a sufficient quantity — 8 to 9-tenths gram — 

 of potassic fluoride, was evaporated on a water bath until the 

 residual mass was simply moist — it was not wet and also not 

 perfectly dry ; for if evaporated to perfect dryness, even at the 

 temperature of a water bath, the subsequent solution in water 

 is apt to be turbid, due to the decomposition of the double 

 fluoride. The moist mass was dissolved in the least possible 

 quantity of boiling water, the solution concentrated a little on 

 the water-bath, and then allowed to cool. The tantalic potassic 

 fluoride will have separated, almost completely, by the time the 

 solution has become cold. After standing for an hour or so 

 the crystals of potassic tantalic fluoride are filtered off and 

 washed with water acidulated with hydrofluoric acid and 

 containing also a little potassic fluoride. The united filtrate 

 and wash-water are again evaporated, when a small amount of 

 the double salt will be obtained. This second crystallization 

 should be examined under the microscope for the plates of" 

 potassic columbic fluoride, the appearance of which is a good 

 indication that the solution has been sufficiently concentrated 

 to allow of the complete separation of the potassic tantalic salt — 

 a third evaporation is seldom necessary. I find this method for 

 the separation of tantalic from columbic acid preferable to that 

 proposed by Rammelsberg, i. e. to fuse with potassic fluoride. 



The method as described yields clear solutions of small vol- 

 ume. The complete but not over- washing of the potassic tan- 

 talic fluoride is the most delicate manipulation in the process. 

 The filtrate containing the columbic acid is evaporated on a 

 water-bath, after the addition of 25-30 drops of concentrated 

 sulphuric acid, so long as aqueous vapor is given off, when it 

 is transferred to a sand bath and a part of the excessive sul- 

 phuric acid expelled, the columbic acid is subsequently thrown 

 down by addition of a sufficient quantity of water and boiling. 

 If the quantity of columbic acid present is large, it is better to 

 add less sulphuric acid, about half so much, and a quantity of 

 potassic hydric sulphate, evaporate to dryness and fuse the 

 mass — the columbic acid obtained by boiling the f used-mass with 

 water is more granular and filters better. The tantalic acid was 

 invariably weighed as Ta^0 5 , after ignition in an atmosphere of 

 amnionic carbonate. The analyses of my specimens presented 

 no other difficulties. 



The hardness of the specimens varied but little from 6, and 

 the fracture as previously stated is uneven, with a tendency to 

 fine granular rather than to sub-conchoidal. The sp. gr. and 

 composition vary not only with locality but with the individual 

 crystals from the same locality to such an extent that from an 



