ON THE IDENTITY OF COLUMBIUM AND TANTALUM. 



27 



ees^ of potasl\ may prevent the appearance of this precipi- 

 tate, so also may a small excess of oxalic or tartaric acids 

 prevent precipitation, or dissolve a precipitate already form- 

 ed. A larger excess of citri^ acid seemed requisite for this 

 purpose, and would also dissolve the galiate of columbium. 

 In each case the precipitate may be made to appear by neu- 

 tralizing the redundant acid ; and for this purpose carbo-^ 

 nate of ammonia should be employed: for although pure 

 ammonia has no power of dissolving the oxide alone, yet 

 the galiate seemed to be perfectly vedissolved by that al- 

 kali. 



When infusion of galls is poured upon the white oxide 

 recently precipitated, and still moi^t, it combines readily, 

 and forms the orange-coloured compound. 



Prussiate of potash occasioned no change in an o^jiide that Prasshteaf 

 had been purified by a second fusion with. potash; but it P*^*^^ 

 a[)peared to dissolve a snnall portion of the oxide, as infu- 

 sion of galls, poured into the clear liquor, occasioned a 

 cloudy precipitate of an orange colour, though no such pre- 

 cipate took place when the itjfusion was naixed with the same' 

 prussiate alone. 



Hidrosulphuret of potash being added to the oxide, and Hidmsralipfeap- 

 heated upon it, impaired ihe whiteness of its appearance/''^'^*^!?®^'*^ 

 and seemed to detect the remains of some impurity, which 

 had not yet been removed by other roeaiis ; but no ap- 

 pearance indicated the formation of a sulphuret of colum- 

 bium. 



From a careful repetition of these experiments upon xheoidraeE 

 each of the oxides, I see no reason to doubt of their per- perfectly smi. 

 feet agreement in all their chemical properties ; but there jj^j'^gj-^is^^gggj. 

 is nevertheless a very remarkable diiference in the speci- in sp«c- S^^- 

 fie gravities of the two minerals from which they are ex- 

 tracted. 



The specific gravity of columbite was ascertained by Mr. very rca-s^feiv 

 Hatchett to be 5'918; that of tantalite was found by Mr. at'b".' 

 Eckeberg to be 7*953 ; and I have every reason to suppose 

 their results correct, since a small fragment of the former 

 .■appeared upon trial to be 5"87, while a spec men of tanta- 

 lite, weighed at the same time, was as much as 7*B. I 

 ifehould, however, observe, that the specific gravities of three 



other 



