divide the residue by 5, and you get the corresponding Twaddell degrees.
If you have Twaddell degrees, simply multiply by 5, and add 1000 to the
result, and you get the specific gravity as usually taken, with water as
the unit, or in this case as 1000. An instrument much used on the
Continent is the Beaumé hydrometer. The degrees (_n_) indicated by this
instrument can be converted into specific gravity (_d_) by the

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°, and on the simpler centigrade one, as
100°, water freezing at 0° C. But if what I have said is true, when we