OF SOME SALTS OF SODA. 83 
losophy, Vol. 1, part 2nd., under the head Carbo- 
nate of Soda, he tells us that he found 100 grains 
of crystals of carbonate of soda by exposure 
to the action of the atmosphere for eight days 
to be reduced to 44 grains; and by a red heat 
to 37 grains. He, therefore, concludes that 
the ordinary efflorescence of this salt is not dry 
carbonate, but one atom of carbonate and one 
of water. And he offers as a confirmation to 
his conclusion, the fact that he found his 37 
grains of calcined residue to again become 44 
grains by exposure to the atmosphere for five 
days. It is evident from the result of my expe- 
riments that he either did not continue his 
exposure long enough, or that the atmosphere 
in the case of his experiment had much more 
drying power than in the case of mine, or he 
would have found the gain of water to have been 
much greater. His conclusion, however, very 
nearly agrees with mine with regard to the 
quantity of water which can be lost by efflores- 
cence, as will be perceived from the experiments 
which I shall mention in the sequel. 
On the 20th October, I put 100 grains of 
crystals (broken small) of pure Carbonate of 
Soda, prepared from the Bi-carbonate, into a 
watch glass; and left them exposed to the 
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