Polytechnic School, an iron cylinder, two feet and a half long and
one foot in diameter, in which carbonic acid had been developed for
experiment before the class, burst, and its fragments were scattered
about with the most tremendous force; it cut off both the legs of
the assistant and killed him on the spot. This vessel, formed of the
strongest cast-iron, and shaped like a cannon, had often been
employed to exhibit experiments in the presence of the students. We
can scarcely think, without shuddering, of the dreadful calamity
such an explosion would have occasioned in a hall filled with
spectators.

When we had ascertained the fact of gases becoming fluid under the
influence of cold or pressure, a curious property possessed by
charcoal, that of absorbing gas to the extent of many times its
volume,--ten, twenty, or even as in the case of ammoniacal gas or
muriatic acid gas, eighty or ninety fold,--which had been long
known, no longer remained a mystery. Some gases are absorbed and
condensed within the pores of the charcoal, into a space several
hundred times smaller than they before occupied; and there is now no
doubt they there become fluid, or assume a solid state. As in a
thousand other instances, chemical action here supplants mechanical
forces. Adhesion or heterogeneous attraction, as it is termed,
acquired by this discovery a more extended meaning; it had never
before been thought of as a cause of change of state in matter; but
it is now evident that a gas adheres to the surface of a solid body
by the same force which condenses it into a liquid.

The smallest amount of a gas,--atmospheric air for instance,--can be
compressed into a space a thousand times smaller by mere mechanical
pressure, and then its bulk must be to the least measurable surface