For analyzing the gases of blast-furnaces the various apparatus of Orsat
have long been employed; but, by reason of its simplicity, the burette
devised by Dr. Bünte, and shown in the accompanying figures, is much
easier to use. Besides, it permits of a much better and more rapid
absorption of the oxide of carbon; and yet, for the lost fractions of
the latter, it is necessary to replace a part of the absorbing liquid
three or four times. The absorbing liquid is prepared by making a
saturated solution of chloride of copper in hydrochloric acid, and
adding thereto a small quantity of dissolved chloride of tin. Afterward,
there are added to the decanted mixture a few spirals of red copper, and
the mixture is then carefully kept from contact with the air.
To fill the burette with gas, the three-way cock, _a_, is so placed that
the axial aperture shall be in communication with the graduated part, A,
of the burette. After this, water is poured into the funnel, t, and the
burette is put in communication with the gas reservoir by means of a
rubber tube. The lower point of the burette is put in communication with
a rubber pump, V (Fig. 2), on an aspirator (the cock, _b_, being left
open), and the gas is sucked in until all the air that was in the
apparatus has been expelled from it. The cocks, _a_ and _b_, are turned
90 degrees. The water in the funnel prevents the gases communicating
with the top. The point of the three-way cock is afterward closed with a
rubber tube and glass rod.
If the gas happens to be in the reservoir of an aspirator, it is made
to pass into the apparatus in the following manner: The burette is
completely filled with water, and the point of the three-way cock is
put in communication with a reservoir. If the gas is under pressure, a
portion of it is allowed to escape through the capillary tube into the
water in the funnel, by turning the cock, _a_, properly, and thus all
the water in the conduit is entirely expelled. Afterward _a_ is turned
180°, and the lower cock, _b_, is opened. While the water is flowing
through _b_, the burette becomes filled with gas.
_Mode of Measuring the Gases and Absorption_.--The tube that
communicates with the vessel, F, is put in communication, after the
latter has been completely filled with water, with the point of the
cock, _b_ (Fig. 2). Then the latter is opened, as is also the pinch cock
on the rubber tubing, and water is allowed to enter the burette through
the bottom until the level is at the zero of the graduation. There are
then 100 cubic centimeters in the burette. The superfluous gas has
escaped through the cock, _a_, and passed through the water in the
funnel. The cock, _a_, is afterward closed by turning it 90°. To
cause the absorbing liquid to pass into the burette, the water in the
graduated cylinder is made to flow by connecting the rubber tube, s, of
the bottle, S, with the point of the burette. The cock is opened, and
suction is effected with the mouth of the tube, r. When the water has
flowed out to nearly the last drop, _b_ is closed and the suction bottle
is removed. The absorbing liquid (caustic potassa or pyrogallate of
potassa) is poured into a porcelain capsule, P, and the point of the
burette is dipped into the liquid. If the cock, _b_, be opened, the
absorbing liquid will be sucked into the burette. In order to hasten
the absorption, the cock, _b_, is closed, and the burette is shaken
horizontally, the aperture of the funnel being closed by the hand during
the operation.
If not enough absorbing liquid has entered, there may be sucked into the
burette, by the process described above, a new quantity of liquid. The
reaction finished, the graduated cylinder is put in communication with
the funnel by turning the cock, _a_. The water is allowed to run from
the funnel, and the latter is filled again with water up to the mark.
The gas is then again under the same pressure as at the beginning.
After the level has become constant, the quantity of gas remaining is
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_.
When an acid solution of chloride of copper is employed, dilute
hydrochloric acid is used instead of water.
Fig. 2 shows the arrangement of the apparatus for the quantitative
analysis of oxide of carbon and hydrogen by combustion. The gas in the
burette is first mixed with atmospheric air, by allowing the liquid to
flow through _b_, and causing air to enter through the axial aperture of
the three way cock, _a_, after cutting off communication at v. Then, as
shown in the figure, the burette is connected with the tube, B, which is
filled with water up to the narrow curved part, and the interior of the
burette is made to communicate with the combustion tube, v, by turning
the cock, a. The combustion tube is heated by means of a Bunsen burner
or alcohol lamp, L. It is necessary to proceed, so that all the water
shall be driven from the cock and the capillary tube, and that it shall
be sent into the burette. The combustion is effected by causing the
mixture of gas to pass from the burette into the tube, B, through the
tube, v, heated to redness, into which there passes a palladium wire.
Water is allowed to flow through the point of the tube, B, while from
the flask, F, it enters through the bottom into the burette, so as to
drive out the gas. The water is allowed to rise into the burette as far
as the cock, and the cocks, _b_ and _b¹_, are afterward closed.
[Illustration: DR. BÜNTE'S GAS BURETTE]
By a contrary operation, the gas is made to pass from B into the
burette. It is then allowed to cool, and, after the pressure has been
established again, the contraction is measured. If the gas burned is
hydrogen, the contraction multiplied by two-thirds gives the original
volume of the hydrogen gas burned. If the gas burned is oxide of carbon,
there forms an equal volume of carbonic acid, and the contraction is the
half of CO. Thus, to analyze CO, a portion of the liquid is removed from
the burette, then caustic potash is allowed to enter, and the process
goes on as explained above.
The total contraction resulting from combustion and absorption,
multiplied by two-thirds, gives the volume of the oxide of carbon.
The hydrogen and oxide carbon may thus be quantitatively analyzed
together or separately.--_Revue Industrielle_.
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