itre can attract phlogiston in varying quantity, when
it likewise receives other properties with each proportion. (_a._) When
it becomes, as it were, saturated with it, a true fire arises, and it is
then completely destroyed. (_b._) When the inflammable principle is
present in smaller quantity, this acid is converted into a kind of air
which will not unite either with the alkalies or with the absorbent
earths, and with water only in very small quantity. When this acid of
nitre, resembling air, meets with the air, the latter takes the
inflammable substance from it again, it loses its elasticity (Sec. 13), the
vapours acquire redness, and the air undergoes at the same time this no
less remarkable than natural alteration, that it is not only diminished,
but also becomes warm. (_c._) When the acid of nitre receives still
somewhat less phlogiston, it is likewise converted into a kind of air,
which, like the air, is also invisible, but unites with the alkalies and
earths, and along with them can bring forth real intermediate salts.
This phlogisticated acid is, however, so loosely united with these
absorbing substances, that even the simple mixture with the vegetable
acids can drive it out. It is present in this condition in nitre which
has been made red hot, and also in _Nitrum Antimoniatum_. When this acid
of nitre meets the air it also loses its elasticity and is converted
into red vapours. When it is mixed in a certain quantity with water,
this acquires a blue, green, or yellow colour. (_d._) When the pure acid
of nitre receives but very little of the inflammable substance, the
vapours only acquire a red colour, and are wanting in expansive power;
it is, however, more volatile than the pure acid. This acid holds this
small quantity of phlogiston so firmly that even the air, which so
strongly attracts the inflammable substance, is not able to separate
this from it.

* * * * *

+29.+ I took a glass retort which was capable of holding 8 ounces of
water, and distilled fuming acid of nitre according to the usual method.
In the beginning the acid went over red, then it became colourless, and
finally all became red again; as soon as I perceived the latter, I took
away the receiver and tied on a bladder, emptied of air, into which I
poured some thick milk of lime (Sec. 22) in order to prevent the corrosion
of the bladder. I then proceeded with the distillation. The bladder
began to expand gradually.