Place a flat saucer containing about a pound of oil of vitriol under
the receiver of the air-pump, and set in it a watch glass containing
a little water, supported on a stand with _glass_ legs. Exhaust the
receiver, when the water will evaporate, but without boiling; and the
vapor being absorbed as it forms by the oil of vitriol, the vacuum
is preserved, and the evaporation continues, until the vapor has
abstracted so much caloric from the remainder of the water that it is
all at once converted into ice.
In most elementary works on chemistry may be found a long table of
freezing mixtures, as they are called, some with and others without
ice or snow. We have selected a few from each division.