60 ' T. 31 Ghatard— Urao. 



The occurrence, in Venezuela, of the mineral urao has been 

 described by Faxar* and by Boussingault.f The latter gives 

 the following analysis : 



Hypoth. Com p. 



Na o 41-22 Na o C0 3 46-98 



C o 39-00 NaHC0 3 .. 37'24 



H„0 18-SO H 3 "14-80 



Imparities 0*98 Impurities. 0*98 



100-00 100-00 



By deducting the impurities from this analysis, Laurent;}: 

 obtained as the formula of the pure salt, 



Na 2 C0 3 , NaHC0 3 -f-2H 2 0. 



The impurities in such salts are insoluble matter, with chloride 

 and sulphate of sodium, all of which can be deducted when we 

 wish to calculate the formula since they are, under the circum- 

 stances, anhydrous and merely diminish the percentage of urao 

 in the material. If we deduct the impurities from this analysis 

 and recalculate the residue to 100 per cent, and likewise calculate 

 the theoretical percentages for the above formula, we shall have ; 



Found. Theoret. Hypoth. Oomp. Theoret. 



Na 2 ... 41-63 41-15 Na„C0 3 ... 47*44 46*90 



CO„ 39-38 38-94 NaHCO, .. 37*61 37*17 



H„0 18*99 19-91 HO 14-95 15*93 



100*00 100*00 100*00 100*00 



If we take the theoretical proportion between the Na 2 C0 3 

 and the NaHC0 3 we have Na 2 C0 3 : Na 2 HC0 3 : : 106 : 84 : : 47*44 

 : 37 - 51 while the amount of NaHC0 3 found in 37*61, a difference 

 of only 0*11 per cent. Hence Boussingault's urao is an almost 

 theoretically pure salt, showing only a small loss of water and a 

 trilling increase of NaHC0 3 . 



The existence of a native sesquicarbonate of sodium, Na 2 C0 3 , 

 2]SraHC0 3 +3H 2 0, to which the mineral name trona has been 

 given, rests on an analysis by Klaproth,§ and under this head 

 the numerous analyses of natural sodas to be found scattered 

 through the literature of the subject have been referred. A 

 careful revision and recalculation of these analyses, in the man- 

 ner described above, show that none of them, excepting those 

 of Popp,|| agree, even reasonably closely, with this formula, 



* Faxar, Ann. de Chimie, IE, ii, 432. 



\ Boussingault, ibid., II, xxix, 110. 



\ Laurent, Ann. de Chimie, III, xxxvi, 348. 



§ Klaproth, Beitrage, iii, p. 83, 1802. 



I Popp, Ann. der Chem. u Pharm., 155, p. 348. 



