An instrument for the speedy volumetric determination of carbonic acid

Abstract

The principle of this instrument is the absorption of carbonic acid in a closed receiver by potassium hydrate, and the accurate measurement of the volume of dry atmospheric air required to re-establish the atmospheric pressure after complete absorption. The volume of air used for that purpose will exactly correspond to that of the carbonic acid gas absorbed. It is obvious that whatever be the reading of the barometer, the volume of air corresponding to that of the carbonic acid absorbed, will give the correct proportion of carbonic acid in the air submitted to' analysis ; but to obtain the weight of the gas present, and its proportion by weight, it will be necessary to reduce both the volumes of air analysed and of carbonic acid found to their volume at 0° (C.), and under a pressure of 760 mm. of mercury. Hence the necessity of recording the height of the barometer at the time of the experiment, or one reading may suffice for a number of determinations. The instrument resembles two small gasometers, and consists of two tanks and two bell-jars, or air-holders, each of the latter being made to hold half a cubic foot of air. The bell-jars hang on a metallic cord which connects them with each other, and passes over two pulleys, allowing the bell-jars to be moved up and down alternately in the tanks. The inside of the bell-jars communicates with the outside air by means of a ⋃ -shaped iron pipe, one limb of which opens inside the bell-jar above the fluid it contains, and the other outside on a somewhat lower level for sake of convenience. The tanks or troughs contain glycerine, over which floats a layer of almond oil an inch or two in thickness, and filling approximately the trough. The opening of the pipe above the surface of the oil enters loosely, so as to leave free passage of air, a neck in the bell-jar admitting a thermometer fitted air-tight through it. By this arrangement when the bell-jar is lowered, the thermometer descends into the inner limb of the ⋃ -pipe or stand-pipe without dipping into the oil or glycerine.