e Davy and Faraday
more than partially to bridge. A long list of gases, including the
familiar oxygen, hydrogen, and nitrogen, resisted all their efforts
utterly--notwithstanding the facility with which hydrogen and oxygen
are liquefied when combined in the form of water-vapor, and the relative
ease with which nitrogen and hydrogen, combined to form ammonia, could
also be liquefied. Davy and Faraday were well satisfied of the truth of
Dalton's proposition, but they saw the futility of further efforts
to put it into effect until new means of producing, on the one hand,
greater pressures, and, on the other, more extreme degrees of cold,
should be practically available. So the experiments of 1823 were
abandoned.

But in 1844 Faraday returned to them, armed now with new weapons, in the
way of better air-pumps and colder freezing mixtures, which the labors
of other workers, chiefly Thilorier, Mitchell, and Natterer, had made
available. With these new means, and without the application of any
principle other than the use of cold and pressure as before, Faraday now
succeeded in reducing to the liquid form all the gases then known with
the exception of six; while a large number of these substances were
still further reduced, by the application of the extreme degrees of
cold now attained, to the condition of solids. The six gases which still
proved intractable, and which hence came to be spoken of as "permanent
gases," were nitrous oxide, marsh gas, carbonic oxide, oxygen, nitrogen,
and hydrogen.

These six refractory gases now became a target for the experiments of a
host of workers in all parts of the world. The resources of mechanical
ingenuity of the time were exhausted in the effort to produce low
temperatures on the one hand and high pressures on the other. Thus
Andrews, in England, using the bath of solid carbonic acid and ether
which Thilorier had discovered, and which produces a degree of cold
of--80 deg. Centigrade, applied a pressure of five hundred atmospheres, or
nearly four tons to the square inch, without producing any change of
state. Natterer increased this pressure to two thousand seven hundred
atmospheres, or twenty-one tons to the square inch, with the same
negative results. The result of Andrews' experiments in particular was
the final proof of what Cagniard de la Tour had early suspected
and Faraday had firmly believed, that pressure alone, regardless of
temperature, is not sufficient to reduce a gas to t