446 Dr. Thomson on Three mw Salts of Soda. [Dec. 



of soda, owing obviously to a little of the sulphur being acidified 

 during the carbonating process ; but the prismatic carbonate 

 contained no sulphuric acid whatever ; neither could I detect in 

 it any sulphur, or sulphuretted hydrogen, by the most delicate 

 tests that I could apply. It remains, therefore, somewhat 

 doubtful, whether the small excess of soda perceptible in the 

 preceding analysis be owing to an error in the experiments, or 

 to the salt containing a small portion of hydrate of soda mixed 

 or combined with the carbonate. 



By the analogy 2-75 : 4 :: 17-283 : 25-136 = soda combined 

 with carbonic acid ; and by subtracting 25*136 from 25*797, we 

 obtain 0*659 for the caustic soda that may be contained in 100 

 grains of the salt. This soda, supposing it present, will be in the 

 state of a hydrate united to 0*185 water, and constituting 0*844 

 grain in weio;ht. Subtracting these quantities, we have 17-283 

 + 25*138 : 56*735 :: 6*75 : 9*027 = the water united in the 

 salt with 6*'^5 of anhydrous carbonate of soda. 



I am rather disposed to admit an excess of soda, or rather the 

 existence of a little hydrate of soda in the salt, because consider- 

 able pains were taken, after the deficiency of carbonic acid was 

 observed, to determine the quantity of carbonic acid with every 

 attention to accuracy, but all the experiments led to precisely 

 the same result ; and if we reckon the carbonic acid from the 

 nitrate of soda, we obtain almost exactly the same weight of 

 carbonic acid as by the direct method.* 



There seems no doubt, from the preceding analysis, that the 

 constituents of prismatic carbonate of soda (supposing it pure) 

 are, 



1 atom carbonic acid 2*75 



1 atom soda. 4*0 



8 atoms water 9*0 



15-75 



• It was shown that 49*35 grains of the pure salt lost by heat 28*09 grains. The 

 remaining 21-26 grains, when decomposed by nitric acid, furnished (12 991 — 0*26) 

 12-731 grains of soda. Hence the 21*26 grains must have been composed of. 



Carbonic acid 8529 



Soda 12-731 



21-260 

 Now 8*5?9 : 12-731 :: 4 : 2'666 = carbonic acid united to 4 soda in the carbonate. 



