60 
DELIQUESCENCE OF BODIES. 
measure of the deliquescence of the salt and its affinity for 
water, we may proceed farther and determine at what degree of 
the hygrometer the deliquescence begins to take place. For 
this purpose it will be sufficient to place the hygrometer under 
a glass moistened with the saline solution, and observe the 
degree indicated after some hours. In this manner it will be 
found, th^t with a saturated solution of muriat of soda at 15 ° 
temperature, the hygrometer will stand at 9O 0 , and that with a 
solution of nitre also made at 15 ° it will stand at about 97°, &c. 
Instance in Hence we may conclude, that muriate of soda will not be 
common salt, deliquescent below 90® of the hygrometer; but that it will 
begin to be so at that term, and will become much more so 
above it. When a table shall have been constructed, indi- 
cating tlie degrees of the hygrometer, corresponding with the 
temperature of ebullition of a certain number of salts, we may 
determine the degree of the hygrometer at which all the others 
will begin to be deliquescent, provided we know the degree of 
ebullition of their solutions in water. 
I need not observe, that what relates to the deliquescent 
salts, is likewise applicable to all the solid or liquid bodies 
which have an affinity for water. According to these princi- 
Sulphuric acid, pies we shall find, that concentrated sulphuric acid can take 
from air completely humid, more than fifteen times its weight 
of water. And from this property, which different saline solu- 
tions possess, of exhibiting different intensities at the same tem- 
perature, it is easy to determine with precision, for every tem- 
perature and degree of the hygrometer, the quantity of vapour 
contained in a given volume of air ; a result which Saussure 
could not obtain, notwithstanding his accuracy, because his 
processes were imperfect. 
Method of de- This method, which I have already pointed out, consists in 
termining the taking liquids, from which nothing is separated by heat but 
vapour in air , , ... , ” _ 
of different water, and boiling them at very different temperatures. For 
temperatures, example, sulphuric acid, more or less diluted, and to place the 
hygrometer under glasses moistened with each of these liquids, 
and observe the degree at which it becomes stationary. On the 
one hand, from my >experiments, the density of aqueous 
, vapour, which is to that of air as 10 to 16 ; and, on the other 
hand, we know the degree of ebullition, or the intensity of 
each liquid enclosed along with the hygrometer, under the 
glass 
