SULPHURIC ACID FOR WATER. 373 
under consideration are concerned, it seems that 
the weight of the atmosphere, by the slight com- 
pression which it exerts, gives some additional 
cohesion to the particles of liquid; or increases 
the affinity existing between the acid and the 
water with which it is diluted, to counterbalance 
which more of the repulsive agency of heat is 
required. 
Having demonstrated that the evaporation of 
water from sulphuric acid is capable of being car- 
ried further in space void of air, than in space. 
under ordinary atmospheric pressure, it becomes 
my duty to state the degree of rarefaction of the 
receivers I have spoken of as exhausted or re- 
garded as vacua, and also to state under what 
degree of pressure the experiments were con- 
ducted, which I have described as conducted un- 
der unexhausted receivers. As I have for some 
years regularly registered the indications of the 
barometer, I am fortunately enabled to furnish 
with tolerable precision both these requisites. In 
every instance of an experiment under rarefied 
air, the exhaustion was such as that the mercury 
gauge indicated a pressure of only 0.9 of an inch; 
this being the utmost degree of rarefaction which 
the state of my pump, during the conducting of 
