OF SOME SALTS OF SODA. 79 
is met, on stating the circumstance to the ma- 
nufacturer, with the reply that he must have 
allowed the article to acquire moisture from the 
atmosphere previously to testing it. This asser- 
tion is often received by the consumer with dis- 
credit, under the supposition that those salts 
of soda—the Sulphate and Carbonate—of which 
the article the subject of dispute principally 
consists being described by scientific writers as 
efflorescent salts, cannot be capable of imbibing 
water from the atmosphere. 
In consequence of a dispute of this kind, I 
exposed to a red heat a quantity of impure car- 
bonate of soda, such as is used by bleachers: I 
then put 50 grains of it into a watch glass, and 
left it exposed to the atmosphere in my labora- 
tory. At the expiration of 23 days I found it to 
have gained 51 grains of water. This was a 
convincing proof that some of the anhydrous 
salts of which this sample was constituted must 
be capable of absording hygrometric water to a 
great amount; and I was consequently urged 
to commence a number of experiments, to deter- 
mine what amount of water the anhydrous car- 
bonate and sulphate of soda are severally capable 
of acquiring, and to decide under what circum- 
stances they really are efflorescent salts. 
