58 
DELIQUESCENCE OF BODIES. 
according to the temperature and the degree of the hygrometer 
at which it begins to be apparent. 
The deliquescence of a body being dependant on its affinity 
for water, and the effect of this affinity being to diminish to a 
certain point, the elastic force of the vapour, contained in a 
determinate volume of air, it becomes very essential, not only 
for ascertaining whether the deliquescence can be shewn, but 
likewise to obtain comparable results, to place each body in an 
atmosphere completely saturated with humidity. By this means 
it is shewn that muriate of soda, sugar, &c. are very deliquescent 3 
that nitre itself and many other bodies, in which this property 
has not been supposed, do possess it in a greater or less degree. 
The degree of This method does not determine the degre£ to which a body 
deliquescence ma y deliquescent 3 but to ascertain this, we must take notice, 
that since the deliquescence of a body depends on its affinity 
for water, and that affinity is itself singularly modified by heat, 
it will be necessary to consider each temperature in particular, 
is determined Suppose, therefore, that it were required to determine the 
atwhieh a*””* degree of deliquescence of any solid, or liquid body, in air 
saturated solu- saturated with moisture at the temperature of 15 degrees 
bod/ boils if centigrade (59 F.) If it be solid, the body must first be dis- 
higber than solved to saturation, and the solution afterwards boiled. If 
fs^flelique^nt ^ 100 degrees (212 F.) which is the boiling point of 
and more so pure water, the body will not be deliquescent 3 but if it boil at 
the higher 3 a higher degree the body will be more deliquescent in propor- 
tion as the boiling point is above 100 *. Thus muriate of soda 
will be very deliquescent in air saturated with humidity 3 for its 
solution in water at 15° does not boil, till it has arrived at 107°>4 
(225 F.) Nitre will be likewise deliquescent, but much less 
than salt, for its solution at 15° boils at 10l°,4 (214,5 F-) 
Whether a 
body be 
deliquescent, 
is shewn by 
placing it in 
air perfectly 
humid. 
The boiling * I must here remark, that instead of taking the boiling point of 
points do not each liquid, it would be more exact to take that of the tension of its 
de^ce/of va P our , at the precise temperature at which the deliquescence is 
deUquesc.enee rc q il ired to be determined, because the elevation of the boiling point 
quite strictly, is not proportional to the quantity of salt held in solution. A similar 
method must necessarily be used to determine the foree with which 
solid bodies attract the vapour of water, without any change of state 
succeeding, as would happen with regard to lime and the salts depriv- 
ed of water of crystallization. I enter fully into this subject in the 
Memoir. 
Experiment 
