GAS. 
metals might be employed for the same 
purpose, but mercury and copper appear 
to afford it in the greatest purity ; and the 
latter is perhaps preferable, because the 
process goes on more regularly with it. 
This gas is colourless, and somewhat 
heavier than atmospheric air. It is ex- 
tremely deleterious, killing even insects 
very quickly, and destroying plants. Water 
deprived of air absorbs about one-ninth ofits 
bulk of this gas, without acquiring any taste 
from it; and a boiling heat expels it again 
unchanged. If the water contain air, the 
gas is partly decomposed, and the absorp- 
tion, though in reality greater, is apparently 
less, from the nitrogen evolved. Water 
impregnated with earthy salts, does not 
absorb so much ; a solution of green sul- 
phate, or green muriate of iron, however, 
absorbs it rapidly, and becomes dark 
brown, and almost opaque. When this is 
effected over mercury, the gas may be 
expelled unchanged by a moderate heat, 
or by placing the solution in a vacuum, 
though perhaps not the whole of it. Solu- 
tions of nitrate of iron, the sulphates of tin , 
and of zinc, and muriate of zinc, likewise 
absorb it. 
Nitrous gas has no acid properties. It 
does not redden vegetable colours, but im- 
pairs them. It extinguishes the flame of 
a candle, or burning sulphur, and the 
phosphoric light of animal substances : but 
lighted charcoal continues to burn in it; 
lighted phosphorus bums in it with great 
splendour, though if not previously kindled 
it may be melted or sublimed in it, without 
taking tire; and Homberg’s pyrophorus 
kindles in it spontaneously. Its most im- 
portant property is its affinity for oxygen 
gas, on account of which it was employed 
by Dr. Priestley, as it still is by many, to 
ascertain the quantity contained in atmos- 
pheric air. See Eudiometer. 
When mixed with oxygen gas red fumes 
arise, heat is evolved, and the two gases, 
if in due proportion and both pure, disap- 
pear, being converted into nitric acid. 
This gas is soluble in nitric acid, and 
alters its properties in some measure, 
without, however, converting it into an 
acid, in a distinct state of oxygenation, as 
some had supposed.. 
Gas, nitrous oxide. This is the gaseous 
oxide of nitrogen, or of azote of some ; a 
compound of nitrogen with a still less pro- 
portion of oxygen than the preceding gas. It 
is not to be obtained certainly with any 
purity, but by the decomposition of nitrate 
of ammonia. For this purpose nitric acid 
diluted with five or fix parts of water, may 
be saturated with carbonate of ammonia, and 
the solution be evaporated by a very gentle 
heat, adding occasionally a little of the 
carbonate, to supply what is carried off. 
The nitrate crystallizes in a fibrous mass, 
unless the evaporation has been carried so 
far as to leave it dry and compact. The 
latter at a heat between 275° and 300° 
sublimes without being decomposed ; at 320° 
it becomes fluid, and is partly decomposed, 
partly sublimed: between 340° and 480° 
it is decomposed rapidly. The fibrous is 
not decomposed below 400°, but a heat 
above 450° decomposes it ; at 600° a lumi- 
nous appearance is produced in the retort, 
and nitric oxide, nitrous oxide, and nitro- 
gen, mixed in various proportions, are 
evolved ; at 700° or 800° an explosion 
takes place. It is best to perform the 
operation over an Argand’s lamp, as the 
heat may thus be brought to the requisite 
degree speedily, and kept from going too 
far. It should be received over water, and 
suffered to stand an hour in contact with 
it, to free it from any nitrate of ammonia 
that may have been sublimed, as well as 
from any acid suspended in it. Dr. Pfaff 
recommends mixing very pure sand with 
the nitrate, to prevent the hazard of ex- 
plosion; and observes, that it is particu- 
larly requisite it should not be contaminated 
with muriatic acid. One pound of the com- 
pact nitrate yields 4.25 cubic feet of gas, and 
a pound of the fibrous nearly five cubic 
feet. 
The most singular property of this gas 
is its hction on the animal system. Dr. 
Priestley had found, that it was fatal to 
animals confined in it. Mr. Davy first 
ventured to respire it, which he did to con- 
siderable extent. When breathed alone 
for a minute or two, and some have gone 
as far as four or five minutes, it generally 
produces a pleasant thrilling, particularly 
in the- chest and extremities, frequently 
with an inclination to laugh, and sometimes 
an irresistible propensity to gesticulation 
and muscular exertion. The mind mean- 
while is often totally abstracted from all 
surrounding objects. Sometimes its effects 
are not entirely dissipated for some hours ; 
and it is remarkable, that, however strong 
they may have been, no sense of debility 
or languor is induced after they have sub- 
sided. On a few individuals, however, 
its effects have been unpleasant and de- 
pressing; in some it has produced con- 
vulsions, and other nervous symptoms; 
and on some it has had no sensible effect. 
