M. Blondlot on the Crystallization of Phosphorus. 383 



which have in their composition no simple ratios, and are not 

 easily transformed into one another except by fusion with alkalies. 

 The first series corresponds to the general formula 



Ta 2 5 . 



It comprehends the natural Tantalite, and the insoluble com- 

 pounds obtained by calcining tantalic acid with alkaline carbo- 

 nates when the latter are in insufficient quantity, or when the 

 calcination has not been strong enough or prolonged enough to 

 give a completely soluble product. 



The second series comprises the perfectly crystallized tanta- 

 lates of potash obtained by melting tantalic acid with these 

 caustic alkalies, or with their carbonates, in excess at a very high 

 temperature. They are represented by the formula? 



4K 2 0,3Ta 2 O 5 , 16H 2 and 4Na 2 0,2Ta 2 O 5 , 24H 2 0. 



The first gives beautiful crystals, isomorphous with those of the 

 corresponding niobate of potash. 



These two salts had been obtained by H. Rose ; and the results 

 which he had obtained by analysis agree better with the formulae 

 which Marignac attributes to them than with those which he fan- 

 cied himself obliged to adopt. 



Fluoride of tantalum forms, with basic fluorides, fluosalts 

 nearly all of which have the ratio 5 : 2 between the proportions of 

 the fluorine of the two elements. The constancy of this ratio 

 leaves no doubt as to the necessity of attributing to this fluoride 

 the formula TaF 5 . 



Except the fluotantalates of potash, of soda, and of ammonia, 

 the other salts of this kind which were prepared are so soluble 

 and even deliquescent that their crystalline form could not be 

 determined. 



The general analogy which exists between the compounds of 

 niobium and those of tantalum ceases to be exhibited by their 

 fluorides ; for there do not appear to be any oxy fluotantalates. 

 The correlation between these two groups of fluorized compounds 

 is only established on a single point, by the existence of a fluo- 

 niobate of potash isomorphous with the fluotantalate. 



The principal characteristic by which ordinary phosphorus is 

 distinguished from red phosphorus is its property of crystallizing ; 

 yet it is by no means easily crystallized, although it possesses the 

 triple property of being fusible, soluble, and volatile. Blondlot, 

 having tried all the ordinary methods, had recourse to that of 

 sublimation*, which he describes as follows. 



The neck of a flask was drawn out, at about an inch from the 

 shoulder, to the thickness of a quill pen; and phosphorus 

 * Comptes Rendus, August 27, 1866. 



