382 M. Marignac on the Compounds of Tantalum. 



bonic acid was simultaneously passed through the solution. It was 

 dissolved in sulphuric acid, and then precipitated by ammonia. 

 The amount of oxide of indium obtained was about 0*1 per cent. 



Marignac gives an abstract* of recent researches on the com- 

 pounds of tantalum. Former researches had led him to attribute 

 to niobic acid the formula Nb 2 9 5 f, and had taught him that 

 this acid and tantalic acid were constantly associated in the mi- 

 neral kingdom, and that they replaced each other without change 

 of crystalline forms ; he accordingly undertook the investigation 

 of the principal compounds of tantalum, to establish for this metal 

 the existence of a modification analogous to that proposed for 

 niobium. 



The first object was to redetermine the atomic weight of the 

 metal. Analyses of chloride of tantalum executed by H. Rose 

 led to the number 172 (H = l, 0=16) for this atomic weight; 

 but probably these analyses, made on a product doubtless con- 

 taining chloride of niobium (for the presence of niobic acid in 

 tantalates was at that time unknown), had given too small a 

 number. The numerous analyses which he had made of the 

 fluotantalates of potash and ammonia led him in fact to raise the 

 number to 182. 



These new determinations of the atomic weights of niobium and 

 of tantalum, compared with those of the two metals which have 

 the greatest analogy to each other (that is, tungsten and molyb- 

 denum), furnish a new and remarkable example of the parallelism 

 which M. Dumas has noted between various series of simple sub- 

 stances forming natural groups. We have in fact, from his de- 

 terminations, 



Molybdenum . 96 Tungsten . 184; 

 and from Marignac' s ; 



Niobium . . 94 Tantalum . 182. 



The new composition admitted for tantalic acid leads to very 

 simple formulae for two bodies which appeared previously to have 

 very complex compositions. The brown oxide of tantalum, 

 which Berzelius obtained by calcining tantalic acid in a crucible 

 lined with carbon, is a binoxide, Ta O 2 . In like manner sulphide 

 of tantalum has, from the concordant analyses of Berzelius, Rose, 

 and Hermann, the composition corresponding to the bisulphide, 

 TaS 2 . 



Tantalic acid appears capable of forming two distinct modifi- 

 cations, analogous to those which Fremy's beautiful researches 

 on stannic and antimonic acids have made us acquainted with. 

 In fact the best-defined salts of this acid belong to two series 



* ComptesRendus, J uly 16, 1866. 

 t Phil. Mag. S. 4. vol.'xxx. p. 445. 



