_Of Nitrous Air._
Nitrous air is procured by dissolving most of the metals, especially
iron, mercury, and copper, in the nitrous acid; but that from mercury
seems to be the purest. Nitrous air produced from copper contains a
mixture of phlogisticated air. Some nitrous air is also obtained from
the solution of all vegetable substances in nitrous acid; whereas animal
substances in the same process yield chiefly phlogisticated air: but in
both these cases there is a mixture of fixed air.
This species of air is likewise produced by impregnating water with
nitrous vapour. This process continues to have this effect after the
water becomes blue, but ceases when it turns green; there not then,
probably, being a sufficient proportion of water. Nitrous air is
likewise produced by volatile alkali passing over red hot manganese, or
green vitriol, when they are yielding dephlogisticated air. This shews
that dephlogisticated air is one ingredient in the composition of
nitrous air, and the same thing appears by pyrophorus burning in it. On
the contrary, when nitrous air is made to pass over red-hot iron,
volatile alkali is produced.
Nitrous air is completely decomposed by a mixture of about half its bulk
of dephlogisticated air, and the produce is nitrous acid. And as nitrous
acid is likewise formed by the union of inflammable and dephlogisticated
air, one principal ingredient in nitrous air must be common to it and
inflammable air, or phlogiston. This air is likewise decomposed by
dephlogisticated nitrous acid, which by this means becomes
phlogisticated. It is also decomposed by a solution of green vitriol,
which by this means becomes black, and when exposed to the air, or
heated, emits nitrous air, and recovers its former colour. These
decompositions of nitrous air seem to be effected by depriving it of
phlogiston, and thereby reducing it to the phlogisticated air originally
contained in it.
This kind of air is diminished to about one fourth of its bulk by a
mixture of iron filings and brimstone, or by heating iron in it, or
calcining other metals in it, when the remainder is phlogisticated air.
All that iron gets in this process is an addition of weight, which
appears to be water, but it loses its phlogiston, so that nitrous air
seems to contain more phlogiston, and less water than phlogisticated
air.
Nitrous air and dephlogisticated air will act upon one another through a
bladder, but in this case there remains about one-fourth of the bulk of
nitrous air, and that is phlogisticated air; so that in this case there
seems to be a conversion of nitrous air into phlogisticated air without
any addition of phlogiston.
Nitrous air is decomposed by pyrophorus, and by agitation in olive oil,
which becomes coagulated by the process. It is also absorbed by spirit
of turpentine, by ether, by spirit of wine, and alkaline liquors.
It is imbibed by charcoal, and both that air which is afterwards
expelled from it by heat, and that which remains unabsorbed, is
phlogisticated air.
Nitrous air resists putrefaction, but is diminished by the animal
substances exposed to it to about a fourth of its bulk, and becomes
phlogisticated air. It is likewise fatal to plants, and particularly to
insects.
When nitrous air is long exposed to iron, it is diminished and brought
into a state in which a candle will burn in it, though no animal can
breathe it. But this peculiar modification of nitrous air, called
_dephlogisticated nitrous air_, is produced with the greatest certainty
by dissolving iron in spirit of nitre saturated with copper,
impregnating water with this air, and then expelling it from the water
by heat. If bits of earthen ware be heated in this dephlogisticated
nitrous air, a great proportion of it becomes permanent air, not
miscible with water, and nearly as pure as common air, so that the
principle of _heat_ seems to be wanting to constitute it permanent air.