646 TANTALUM. 



fifths of what is extracted from that mineral, by the ordinary 

 process, as oxide of cerium. This throws considerable un- 

 certainty over our knowledge of cerium, as the observations 

 of chemists have not been made upon a pure substance. The 

 new element alters but little the properties of cerium, and lies, 

 therefore, as if concealed in it ; it was that fact which induced 

 M. Mosander to apply the name lantanum to the new metal. 

 The oxide of lantanum is not reduced by potassium, but this 

 metal separates from the chloride of lantanum a grey metallic 

 powder, which undergoes oxidation in water, with disengage- 

 ment of hydrogen gas, changing into a white hydrate. 



Oxide of lantanum. Tt is prepared by calcining the nitrate 

 of cerium as it is mixed with nitrate of lantanum. The oxide 

 of cerium loses its solubility in very dilute acids, while the 

 oxide of lantanum may be taken up by nitric acid diluted with 

 100 parts of water. The ignited oxide of lantanum has a brick 

 red colour, which does not appear to be due to oxide of cerium. 

 It changes in hot water into a white hydrate, which makes red 

 litmus paper blue. This oxide is so powerful a base, that when 

 digested in a solution of sal ammoniac, it dissolves by degrees, 

 expelling the ammonia. The atomic weight of lantanum is 

 smaller than that assigned to cerium or rather to the mixture 

 of the two metals, but has not been accurately determined. 



Sulphuret of lantanum is produced on heating the oxide 

 strongly in the vapour of the sulphuret of carbon. It is pale 

 yellow, decomposes water with disengagement of sulphuretted 

 hydrogen, and becomes the hydrated oxide. 



The salts of lantanum have an astringent taste without any 

 mixture of sweetness. Their crystals have generally a rose 

 tint 5 sulphate of potash produces a precipitate in them, only 

 when they are mixed with salts of cerium. 



TANTALUM. 



Syn. COLUMBIUM. Eg. 2307.4 or 184.9; Ta. 



This metal appears to have been first observed in 1801, by 

 Mr. Hatchett, in a black mineral belonging to the British 

 Museum, and supposed to have come from Massachusets in 

 North America, and was named columbium on that account. 

 M. Ekeberg found a new metal in 1802, which he called tan- 

 talum, in two Swedish minerals, then new, and named by him 



