My dear Sir,

In my former letter I reminded you that three of the supposed
elements of the ancients represent the forms or state in which all
the ponderable matter of our globe exists; I would now observe, that
no substance possesses absolutely any one of those conditions; that
modern chemistry recognises nothing unchangeably solid, liquid, or
aeriform: means have been devised for effecting a change of state in
almost every known substance. Platinum, alumina, and rock crystal,
it is true, cannot be liquified by the most intense heat of our
furnaces, but they melt like wax before the flame of the
oxy-hydrogen blowpipe. On the other hand, of the twenty-eight
gaseous bodies with which we are acquainted, twenty-five may be
reduced to a liquid state, and one into a solid. Probably, ere long,
similar changes of condition will be extended to every form of
matter.

There are many things relating to this condensation of the gases
worthy of your attention. Most aeriform bodies, when subjected to
compression, are made to occupy a space which diminishes in the
exact ratio of the increase of the compressing force. Very
generally, under a force double or triple of the ordinary
atmospheric pressure, they become one half or one third their former
volume. This was a long time considered to be a law, and known as
the law of Marriotte; but a more accurate study of the subject has
demonstrated that this law is by no means of general application.
The volume of certain gases does not decrease in the ratio of the
increase of the force used to compress them, but in some, a