formula: _d_ = 144.3/(144.3 - n)

_Ebullition or Boiling of Water, Steam._--The atmosphere around us is
composed of a mixture of nitrogen and oxygen gases; not a compound of
these gases, as water is of hydrogen and oxygen, but a mixture more like
sand and water or smoke and air. This mass of gases has weight, and
presses upon objects at the surface of the earth to the extent of 15 lb.
on the square inch. Now some liquids, such as water, were it not for
this atmospheric pressure, would not remain liquids at all, but would
become gases. The pressure thus tends to squeeze gases together and
convert them into liquids. Any force that causes gases to contract will
do the same thing, of course--for example, cold; and _ceteris paribus_
removal of pressure and expansion by heat will act so as to gasify
liquids. When in the expansion of liquids a certain stage or degree is
reached, different for different liquids, gas begins to escape so
quickly from the liquid that bubbles of vapour are continually formed
and escape. This is called ebullition or boiling. A certain removal of
pressure, or expansion by heat, is necessary to produce this, _i.e._ to
reach the boiling-point of the liquid. As regards the heat necessary for
the boiling of water at the surface of the earth, _i.e._ under the
atmospheric pressure of 15 lb. on the square inch, this is shown on the
thermometer of Fahrenheit as 212 deg., and on the simpler centigrade one, as
100 deg., water freezing at 0 deg. C. But if what I have said is true, when we
remove some of the atmospheric pressure, the water should boil with a
less heat than will cause the mercury in the thermometer to rise to 100 deg.
C., and if we take off all the pressure, the water ought to boil and
freeze at the same time. This actually happens in the Carre ice-making
machine. The question now arises, "Why does the water freeze in the
Carre machine?" All substances require certain amounts of heat to enable
them to take and to maintain the liquid state if they are ordinarily
solid, and the gaseous state if ordinarily liquid or solid, and the
greater the change of state the greater the heat needed. Moreover, this
heat does not make them warm, it is simply absorbed or swallowed up, and
becomes latent, and is merely necessary to maintain the new condition
assumed. In the case of the Carre machine, liquid water is, by removal
of the atmospheric pressure, coerced, as it were, to take the gaseous
form. But to do