SULPHURIC ACID FOR WATER. 363 
sure anhydrous, as was required to render a 
vacuum of the same temperature anhydrous. 
And, accordingly, on the 1st of November, 1837, 
I commenced two comparative experiments, with 
the view of acquiring this desirable information. 
EXPERIMENTS IIl. AND IV. 
Into one light evaporating dish of 2% inches in 
diameter I put 200 grains of the sulphuric acid, 
sp. gr. 1.8428, and diluted it with 24 grains of 
water, (attending to the precautions mentioned 
in the instances of the former experiments). 
The dish, with its contents, was then placed upon 
an air-pump plate, along with another glass vessel 
of an equal diameter, containing several hundred 
grains of the concentrated acid, and covered with 
a receiver, which was immediately exhausted as 
much as the capability of the pump would allow. 
Into another light dish of the same diameter I 
also put 200 grains of the acid, sp. gr. 1.8428, 
which I diluted with 24.2 grains of water. This 
dish, with its contents, was placed upon a ground 
brass plate, similar to that of the air-pump, along 
with another glass vessel of an equal diameter, 
containing several hundred grains of the concen- 
trated acid, and covered with an air-pump receiver, 
