lly
and filled with water, which was kept thoroughly mixed by means of
agitators. This second vessel stood inside a third one, the sides and
bottom of which were covered with the skins of swans with the down on,
and the whole was immersed in a fourth vessel tilled with water, kept
at the average temperature of the laboratory. Suitable thermometers of
great delicacy were provided, and all manner of precautions were taken
to prevent loss of heat.

[Illustration: THE GENERATION OF STEAM. Fig 1.]

It is impossible not to admire the ingenuity and skill exhibited in
the details of the apparatus, in the various accessories for
generating and storing the gases used, and for absorbing and weighing
the products of combustion; but it is a matter of regret that the
experiments should have been carried out on so small a scale. For
example, the little cage which held the solid fuel tested was only 5/8
inch diameter by barely 2 inches high, and held only 38 grains of
charcoal, the combustion occupying about sixteen minutes. Favre and
Silbermann adopted the plan of ascertaining the weight of the
substances consumed by calculation from the weight of the products of
combustion. Carbonic acid was absorbed by caustic potash, as also was
carbonic oxide, after having been oxidized to carbonic acid by heated
oxide of copper, and the vapor of water was absorbed by concentrated
sulphuric acid. The adoption of this system showed that it was in any
case necessary to analyze the products of combustion in order to
detect imperfect action. Thus, in the case of substances containing
carbon, carbonic oxide was always present to a variable extent with
the carbonic acid, and corrections were necessary in order to
determine the total heat due to the complete combination of the
substance with oxygen. Another advantage gained was that the
absorption of the products of combustion prevents any sensible
alteration in the volumes during the process, so that corrections for
the heat absorbed in the work of displacing the atmosphere were not
required. The experiments on various substances were repeated many
times. The mean results for those in which we are immediately
interested are given in Table I., next column.

Comparison with later determinations have established their
substantial accuracy. The general conclusion arrived at is thus
stated:

"As a rule there is an equality between the heat disengaged or
absorbed in the acts, respectively, of chemical c