204 On the Identity of Columhium and Tantalum* 



If to the alkaline solution of either of them there be 

 added infusion of galls, prussiate of potash, or hydnjsul- 

 phuret of potash, no precipitate occurs ; but when a suffi- 

 cient quantity of acid has been added to neutralize the re- 

 dundant alkali, the infusion of galls will then occasion an 

 orange precipitate; but prussiate oF potash causes no pre- 

 cipitate, nor does the hydrosulphuret precipitate the oxide, 

 although the solution may become turbid from precipita- 

 tion of sulphur by a redundant acid. 



The characteristic precipitant of columbium is consc* 

 quentlv the infusion of galls ; but in the employment of 

 this test certain precautions are necessary. For as an ex- 

 cess of potash may prevent the appearance of this preci- 

 pitate, so also may a small excei.3 of oxalic or tartaric acids 

 prevent precipitation, or dissolve a precipitate already 

 formed. A larger excess oF citric acid seemed requisite for 

 that purpose, and would also dissolve the gallat of colum- 

 bium. In ea«^h case the precipitate may be made to ap- 

 pear by neutralizing the redundant acid ; and for this pur- 

 pose carbonate of ammonia should be employed ; for al- 

 though pure ammonia has no power of dissolving the oxide 

 alone, yet the gallat seemed to be perfectly redissolved by 

 that alkali. 



When infusion of galls is poured upon the white oxide 

 recently precipitated, and still moist, it combines readily, 

 and forms the orange- coloured compound. 



Prussiate of potash occasioned no change in an oxide 

 that had been purified by a second fusion with potash ; but 

 it appeared to dissolve a small portion of the oxide, as in- 

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

 cloudy precipitate of an orange colour, though no such 

 precipitate took place when the infusion was mixed with 

 the same prussiate alone. 



Hydrosulphuret of potash being added to the oxide, and 

 heated upon it, impaired the whiteness of its appearance, 

 and seemed to detect the remains of some impurity which had 

 not yet been removed by other means ; but no appearance 

 indicated the formation of a sulphuret of columbium. 



From a careful repetition of these experiments upcm each 

 of the oxides, I see no reason to doubt of their perfect 

 agreement in all their chemical properties ; but there is 

 nevertheless a very remarkable difference in the specific 

 gravities of the two minerals from which they are ex- 

 tracted. 



The specific gravity of columbitc was ascertained by Mr. 

 Hatchctt ^o be 5-918 ; that of tantalite was found by M. 



Ekebero 



