measured. The contraction that has taken place gives, in hundredths of
the total volume, the volume of the gas absorbed.

When it is desired to make an analysis of smoke due to combustion,
caustic potassa is first sucked into the burette. After complete
absorption, and after putting the gas at the same pressure, the
diminution gives the volume of carbonic acid.

To determine the oxygen in the remaining gas, a portion of the caustic
potash is allowed to flow out, and an aqueous solution of pyrogallic
acid and potash is allowed to enter. The presence of oxygen is revealed
by the color of the liquid, which becomes darker.

The gas is then agitated with the absorbing liquid until, upon opening
the cock, _a_, the liquid remains in the capillary tube, that is to say,
until no more water runs from the funnel into the burette. To make a
quantitative analysis of the carbon contained in gas, the pyrogallate of
potash must be entirely removed from the burette. To do this, the liquid
is sucked out by means of the flask, S, until there remain only a few
drops; then the cock, _a_, is opened and water is allowed to flow from
the funnel along the sides of the burette. Then _a_ is closed, and
the washing water is sucked in the same manner. By repeating this
manipulation several times, the absorbing liquid is completely removed.
The acid solution of chloride of copper is then allowed to enter.

As the absorbing liquids adhere to the glass, it is better, before
noting the level, to replace these liquids by water. The cocks, _a_ and
_b_, are opened, and water is allowed to enter from the funnel, the
absorbing liquid being made to flow at the same time through the cock,
_b_.