212 STEAM BOILERS, ENGINES, AND TURBINES
passing into a tank filled with caustic potash, this forming the usual
seal, and the bell contains a number of concentric tubes in communi-
cation with each other, their surfaces being wetted with the caustic
potash solution. The flue gases to be measured are made to pass
into the bell, and over the whole of the surfaces of the concentric
tubes, and the quantity of CO₂ absorbed is measured by the amount
the bell falls, this being marked on the scale S, shown on the right,
and also by a line on the chart, as with the Sarco. Fig. 85 shows
two charts taken with the Simmance and Abady apparatus.
The Orsat Apparatus for Flue Gas Analysis
This apparatus is designed for a more accurate analysis of the
flue gases, but it does not give a continuous record, as the others that
have been described do. It has three absorbing apparatus, designed
to absorb carbonic acid, oxygen, and carbonic oxide, the absorption of
these forming a complete analysis of the flue gases. It will be
evident that while the apparatus that have been described for giving
a continuous record of the carbonic acid present in the flue gases,
forms a very valuable check upon the stoking and the working of
the boilers generally, it is not so complete as the analysis which
gives the full percentage of the other gases present. In the vessel
that is to absorb carbonic acid, a solution of caustic potash is held,
made by dissolving one part by weight of caustic potash in 2
parts of water in that for oxygen, pyrogallol, made by dissolving
one part by weight of pyrogallic acid in two parts of hot water, and
three parts of the caustic potash solution made for the absorption
of CO₂. In the vessel for absorbing carbonic oxide, a solution of
cuprous chloride is held, made by dissolving one part by weight of
cuprous chloride in seven parts of hydrochloric acid, adding two
parts of copper clippings, allowing to stand for twenty-four hours,
and then adding three parts of water.
As in the other apparatus described, exactly 100 cubic centi-
meters of the flue gases are drawn for examination, and are passed.
into a graduated measuring burette. The measuring burette is
surrounded by a vessel of water, so that the temperature of the gas.
in the burette may be maintained constant. The lower part of the
burette is connected to a bottle by a flexible tube, and the gases are
drawn into the burette, and thence forced into the absorption vessels
in succession, by raising and lowering the bottle, and opening the
cocks leading to the different vessels in succession. For rapid work,
an aspirator must be employed to draw the gas into the apparatus.
