2 Experiments on the 
specific difference between the constitution of 
steam at a high temperature, and that pro- 
duced at the common boiling point. Every 
body knows, that water, in the open air, boils 
at 212 degrees of Fahrenheit; but in a Papin’s 
digester, or closed vessel, or under the pres- 
sure of a column of mercury, it may be heated 
very considerably above 212° without boiling 
at all. In the exhausted receiver of an air- 
pump it boils much below 212°, the boiling 
point in this and all the other cases depending 
- upon the superincumbent pressure.—So that 
water always begins to boil in the open air 
when the elasticity or force of the steam be- 
comes equal, or a little more than equal, to 
the pressure of the atmosphere. The force of 
steam, therefore, of the temperature of 212°, 
is equal to the weight of the atmosphere, or 
to a column of niercury of about 30 inches 
high. But this force is very rapidly increased 
by increasing the temperature ;—so that if 
steam, in contact with water, is heated to 
about 40° above the boiling pomt, the force 
is doubled, and it becomes capable of sustain- 
ing a column of mercury of 60 inches: and 
if the temperature is raised about 55° still 
higher, or to 307°, the steam is then equal to 
four atmospheres, or 120 inches of mercury. 
I make these statements from the table that 
