94 EFFLORESCING PROPERTIES 
66° of temperature. It consequently follows 
that at the temperature of 66° crystals of car- 
bonate of soda can only retain their water of 
crystallization when the vapour point is not 
lower than 58°. According to this rule are 
arranged the following columns of figures. 
The figures uppermost in each column are 
the degrees up to which the atmosphere must 
be saturated with vapour when the temperature 
is equal to the degrees next immediately below, 
in order that the salt exposed to that atmosphere 
shall not effloresce. 
Carbonate of Soda. Sulphate of Soda. 
20° 30 
38 414 
49 50 
58 58 
66 65 
72 70 
17 75 
194 
Being afforded such simple means of procur- 
ing the salts under consideration with neither 
more nor less water than what is actually indis- 
pensable to their existence in the crystallized 
state, I was led to investigate the several per 
centages of water: and in doing so have adopted 
