84 EFFLORESCING PROPERTIES 
atmosphere of the same room. The glass and 
contents were weighed every day for more than 
a fortnight. By one day’s exposure a loss of 
weight of 24 grains was sustained; but, after- 
wards not the slightest loss took place, even 
though the exposure was continued till the 4th 
December, nor was the least efflorescence per- 
ceptible from the beginning to the end of the 
experiment. The crystals retained perfect tran- 
sparency. 
The 2: grains of water lost by the first day’s 
exposure was not belonging to the constitution 
of the crystals : it must only have been sticking 
about them in consequence of their having been 
imperfectly dried, notwithstanding that I had 
previously dried them with blotting paper as 
well as I thought they could have been. 
I have also kept exposed to the like atmos- 
phere for several weeks a very few broken crys- 
tals widely spread over a large surface of glass, 
but no efflorescence in that case took place. 
On the 23rd October, I put 100 grains of 
crystals of pure Sulphate of Soda, prepared by 
neutralizing the Bi-carbonate with sulphuric 
acid, and which I had dried with blotting paper 
