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.