Procedure.—­ Weigh out into the flask (B) about 1 gram of limestone.  Cover it with 15 cc. of water.  Weigh the absorption apparatus (F) or (F’) accurately after allowing it to stand for 30 minutes in the balance case, and wiping it carefully with a lintless cloth, taking care to handle it as little as possible after wiping (Note 1).  Connect the absorption apparatus with (e) and (f).  If a soda-lime tube is used, be sure that the arm containing the soda lime is next the tube (E) and that the glass stopcocks are open.

To be sure that the whole apparatus is airtight, disconnect the rubber tube from the flask (A), making sure that the tubes (a) and (b) do not contain any hydrochloric acid, close the pinchcocks (a) and (k) and open (h).  No bubbles should pass through (D) or (G) after a few seconds.  When assured that the fittings are tight, close (h) and open (a) cautiously to admit air to restore atmospheric pressure.  This precaution is essential, as a sudden inrush of air will project liquid from (D) or (F’).  Reconnect the rubber tube with the flask (A).  Open the pinchcocks (a) and (k) and blow over about 10 cc. of the hydrochloric acid from (A) into (B).  When the action of the acid slackens, blow over (slowly) another 10 cc.

The rate of gas evolution should not exceed for more than a few seconds that at which about two bubbles per second pass through (G) (Note 2).  Repeat the addition of acid in small portions until the action upon the limestone seems to be at an end, taking care to close (a) after each addition of acid (Note 3).  Disconnect (A) and connect the rubber tubing with the soda-lime tube (K) and open (a).  Then close (k) and open (h), regulating the flow of water from (H) in such a way that about two bubbles per second pass through (G).  Place a small flame under (B) and !slowly! raise the contents to boiling and boil for three minutes.  Then remove the burner from under (B) and continue to draw air through the apparatus for 20-30 minutes, or until (H) is emptied (Note 4).  Remove the absorption apparatus, closing the stopcocks on (F) or stoppering the open ends of (F’), leave the apparatus in the balance case for at least thirty minutes, wipe it carefully and weigh, after opening the stopcocks (or removing plugs).  The increase in weight is due to absorption of Co_{2}, from which its percentage in the sample may be calculated.

After cleaning (B) and refilling (H), the apparatus is ready for the duplicate analysis.

[Note 1:  The absorption tubes or bulbs have large surfaces on which moisture may collect.  By allowing them to remain in the balance case for some time before weighing, the amount of moisture absorbed on the surface is as nearly constant as practicable during two weighings, and a uniform temperature is also assured.  The stopcocks of the U-tube should be opened, or the plugs used to close the openings of the Geissler bulb should be removed before weighing in order that the air contents shall always be at atmospheric pressure.]