mercury, and placed it with its mouth downwards in a dish B, likewise
filled with mercury, and having introduced about two gross of water into
the jar, which rose to the top of the mercury at CD; we then plunged the
whole apparatus into an iron boiler EFGH, full of boiling sea-water of
the temperature of 85 (123.25 ), placed upon the furnace GHIK.
Immediately upon the water over the mercury attaining the temperature of
80 (212 ), it began to boil; and, instead of only filling the small
space ACD, it was converted into an aeriform fluid, which filled the
whole jar; the mercury even descended below the surface of that in the
dish B; and the jar must have been overturned, if it had not been very
thick and heavy, and fixed to the dish by means of iron-wire.
Immediately after withdrawing the apparatus from the boiler, the vapour
in the jar began to condense, and the mercury rose to its former
station; but it returned again to the aeriform state a few seconds after
replacing the apparatus in the boiler.
We have thus a certain number of substances, which are convertible into
elastic aeriform fluids by degrees of temperature, not much superior to
that of our atmosphere. We shall afterwards find that there are several
others which undergo the same change in similar circumstances, such as
muriatic or marine acid, ammoniac or volatile alkali, the carbonic acid
or fixed air, the sulphurous acid, &c. All of these are permanently
elastic in or about the mean temperature of the atmosphere, and under
its common pressure.
All these facts, which could be easily multiplied if necessary, give me
full right to assume, as a general principle, that almost every body in
nature is susceptible of three several states of existence, solid,
liquid, and aeriform, and that these three states of existence depend
upon the quantity of caloric combined with the body. Henceforwards I
shall express these elastic aeriform fluids by the generic term _gas_;
and in each species of gas I shall distinguish between the caloric,
which in some measure serves the purpose of a solvent, and the
substance, which in combination with the caloric, forms the base of the
gas.
To these bases of the different gases, which are hitherto but little
known, we have been obliged to assign names; these I shall point out in
Chap. IV. of this work, when I have previously given an account of the
phenomena attendant upon the heating and cooling of bodies, and when I
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