_Of the Doctrine of Phlogiston and the Composition of Water._
It was supposed to be a great discovery of Mr. Stahl, that all
inflammable substances, as well as metals, contain a principle, or
substance, to which he gave the name of phlogiston, and that the
addition or deprivation of this substance makes some of the most
remarkable changes in bodies, especially that the union of a metallic
calx and this substance makes a metal; and that combustion consists in
the separation of phlogiston from the substances that contain it. That
it is the same principle, or substance, that enters into all inflammable
substances, and metals, is evident, from its being disengaged from any
of them, and entering into the composition of any of the others. Thus
the phlogiston of charcoal or inflammable air becomes the phlogiston of
any of the metals, when the calx is heated in contact with either of
them.
On the contrary, Mr. Lavoisier and most of the French chemists, are of
opinion, that there is no such principle, or substance, as phlogiston;
that metals and other inflammable bodies are simple substances, which
have an affinity to pure air; and that combustion consists not in the
separation of any thing from the inflammable substance, but in the union
of pure air with it.
They moreover say, that water is not, as has been commonly supposed, a
simple substance, but that it consists of two elements, viz. pure air,
or _oxygene_, and another, to which they give the name of _hydrogene_,
which, with the principle of _heat_, called by them _calorique_, is
inflammable air.
The principal fact adduced by them to prove that metals do not lose any
thing when they become calces, but only gain something, is, that mercury
becomes a calx, called _precipitate per se_, by imbibing pure air, and
that it becomes running mercury again by parting with it.
This is acknowledged: but it is almost the only case of any calx being
revived without the help of some known phlogistic substance; and in this
particular case it is not absurd to suppose, that the mercury, in
becoming precipitate per se, may retain all its phlogiston, as well as
imbibe pure air, and therefore be revived by simply parting with that
air. In many other cases the same metal, in different states, contains
more or less phlogiston, as cast iron, malleable iron, and steel. Also
there is a calx of mercury made by the acid of vitriol, which cannot be
revived without the help of inflammable air, or some other substance
supposed to contain phlogiston: and that the inflammable air is really
imbibed in these processes, is evident, from its wholly disappearing,
and nothing being left in the vessel in which the process is made beside
the metal that is revived by it. If precipitate per se be revived in
inflammable air, the air will be imbibed, so that running mercury may
contain more or less phlogiston.
The antiphlogistians also say, that the diminution of atmospherical air
by the burning of phosphorus is a proof of their theory; the pure air
being imbibed by that substance, and nothing emitted from it. But there
is the same proof of phosphorus containing phlogiston, that there is of
dry flesh containing it; since the produce of the solution of it in
nitrous acid, and its effect upon the acid, are the same, viz. the
production of phlogisticated air, and the phlogistication of the acid.
Their proof that water is decomposed, is, that in sending steam over hot
iron, inflammable air (which they suppose to be one constituent part of
it) is procured; while the other part, viz. the oxygene, unites with the
iron, and adds to its weight. But it is replied, that the inflammable
air may be well supposed to be the phlogiston of the iron, united to
part of the water, as its base, while the remainder of the water is
imbibed by the calx; and that it is mere water, and not pure air, or
oxygene, that is retained in the iron, is evident, from nothing but pure
water being recovered when this calx of iron is revived in inflammable
air, in which case the inflammable air wholly disappears, taking the
place of the water, by which it had been expelled.
In answer to this it is said, that the pure air expelled from the calx
uniting with the inflammable air in the vessel, recomposes the water
found after this process. But in every other case in which any substance
containing pure air is heated in inflammable air, though the inflammable
air be in part imbibed, some _fixed air_ is produced, and this fixed air
is composed of the pure air in the substance and part of the inflammable
air in the vessel. Thus, if _minium_, which contains pure air, and
_massicot_, which contains none, be heated in inflammable air, in both
the cases lead will be revived by the absorption of inflammable air; but
in the former case only, and not in the latter, will fixed air be
produced. The calx of iron, therefore, having the same effect with
massicot, when treated in the same manner, appears to contain no more
pure air than massicot does.
Besides this explanation of the facts on which the new theory is
founded, which shews it to be unnecessary, the old hypothesis being
sufficient for the purpose, some facts are alledged, as inconsistent
with the new doctrine.
If the calx of iron made by water, and charcoal made by the greatest
degree of heat, be mixed together, a great quantity of inflammable air
will be produced; though, according to the new theory, neither of these
substances contained any water, which they maintain to be the only
origin of it. But this fact is easily explained upon the doctrine of
phlogiston; the water in this calx uniting with the phlogiston of the
charcoal, and then forming inflammable air; and it is the same kind of
inflammable air that is made from charcoal and water.
Also the union of inflammable and pure air, when they are fired together
by means of the electric spark, produces not pure water, as, according
to the new theory, it ought to do, but _nitrous acid_.
To this it has been objected, that the acid thus produced came from the
decomposition of phlogisticated air, a small portion of which was at
first contained in the mixture of the two kinds of air. But when every
particle of phlogisticated air is excluded, the strongest acid is
procured.
They find, indeed, that by the slow burning of inflammable air in pure
air, they get pure water. But then it appears, that whenever this is the
case, there is a production of phlogisticated air, which contains the
necessary element of nitrous acid; and this is always the case when
there is a little surplus of the inflammable air that is fired along
with the pure air, as the acid is always procured when there is a
redundancy of pure air.
That much water should be procured by the decomposition of these kinds
of air, is easily accounted for, by supposing that water, or steam, is
the basis of these, as well as of all other kinds of air.
Since air something better than that of the atmosphere is constantly
produced from water by converting it into vapour, and also by removing
the pressure of the atmosphere, and these processes do not appear to
have any limits; it seems probable, that _water_ united to the principle
of _heat_; constitutes atmospherical air; and if so, it must consist of
the elements of both dephlogisticated and phlogisticated air; which is a
supposition very different from that of the French chemists.