Page 476 - My FlipBook

474 DENTAL MEDICINE.
of fifty atmospheres at a temperature of 40° F., and may be kept
in the iron cylinders for an indefinite period. The advantages
of the condensed form of the gas are its purity, convenience
for use whenever needed, the large supply which can be kept
for use, and the freedom from deterioration, notwithstanding its
age.
Nitrous oxide is an elastic, colorless gas, with a faint, but
agreeable odor and a sweetish taste, which it imparts to water.
Under a pressure of fifty atmospheres at about 40° F., it becomes a
clear, colorless liquid, and at about 148° F. below zero, it freezes
into a beautiful, clear crystalline solid. By the evaporation of
this solid, a degree of cold may be produced far below that of
carbonic acid bath in vacuo, or lower than 170° F. The wash-
ing of nitrous oxide gas, and the retention of it over water for
any length of time, is attended with considerable loss, as much of
is absorbed, especially if the water
it is cold ; such loss may be
avoided to a great extent by using water of an elevated tempera-
ture or a strong solution of common salt. The impurities of
nitrous oxide gas are air, water, nitric oxide or binoxide of nitro-
gen, chlorine and hyponitric acid. The mixture with air which
may occur in the receiver, or when the patient is inhaling the
gas, merely dilutes it as does also the vapor of water. Nitric
oxide, however, is a dangerous impurity, and with others may be
generated even when pure nitrate of ammonia is used in pre-
paring the gas j this impurity is also one of the most difficult to
separate from the gas. Like nitrous oxide, nitric oxide is a
colorless gas, lighter and less soluble in water, and if it is gener-
ated is liable to pass through the washing solutions into the gas-
ometer or receiver; nitric oxide, however, need not be generated
if the proper care is observed with regard to the degree of heat
under the retort which contains the nitrate of ammonia.
Chlorine is also a dangerous impurity, and may be set free if
the salt nitrate of ammonia contains muriate of ammonia (sal-
ammoniac) and chloride of ammonium. To prevent such con-
tamination, the tests of the salts before referred to may be made.
Nitrous oxide gas supports combustion with almost the same
promptness as pure oxygen ; and although nearly identical in