330 Mr Haidinger's Notice respecting Troi/a, 



and settles on the banks of numerous smoking Jakes. Great 

 quantities of it are brought by the merchants of Fezzan to be 

 shipped at Tripoli. It is used in Morocco as an ingredient 

 in the red dye of the leather, and in other manufactures. It 

 forms part of the domains of the crown.* 



The difference between the chemical composition of the 

 two substances, though evident in itself at the time when it 

 was discovered, has only of late received a rule in the doc- 

 trine of fixed proportions, and becomes doubly interesting 

 when compared in this point of view. The analysis of hemi- 

 prismatic natron- salt, by Klaproth, gives 



The formula by Berzelius, Na C- + 20 Aq., making use at 

 the same time of his numbers, gives this proportion : 



The results of the analysis of Trona, by Klaproth, and 

 of an analysis by Mariano de Rivero,-f- instituted with a native 

 carbonate of soda, from the Lake of Merida, in Columbia, are 

 the following : 



Fezzan. Columbia. 

 Soda, - - 37-00 41.22 



Carbonic acid, - 38.00 39.00 



Water, - - 22-50 18.80 



The 2.5 per cent, of sulphate of soda, in the analysis by 

 Klaproth, not being considered as essential, the first of these 

 results agrees very nearly with the formula, Na C 3 +4 Aq., 

 or, 



Soda, - - 37.99 



Carbonic acid, - 40-15 



Water, - - 21-86 



particularly, if we suppose that a small portion of the water 



" Playfair's Geography, vol. vi. p. 167. Horneman's Travels in Africa 

 t Edin. Phil. Journ. vol. xi- p. 215. 



