44 



THE COJIPOSITIONVOF EXPIRED AIR, 



The determinations of the proportions of COj and of O in the air of (he jar at the end of the 

 experiments were made with the Bunte gas burette represented in Fig. 6. For rapid determinations 

 this apparatus gives quite satisfactory results, and one soon learns to manage it easily and obtain 

 results concordant with those obtained by other methods. It is not claimed that the results so 

 obtained are absolutely accurate, but any error resulting from the use ot this burette is a constant 

 one in all the air analyses for the different experiments reported on, and is without influence on 

 the results obtained. 



(I represents the burette proper ; the upi)er portion is of larger size than the lower, which is 

 marked with a scale extending from zero near the bottom to loo c. c. just below the expanded por- 

 tion above, and from the zero mark down to lo c. c. near the lower 

 extremity of the tube. The capacity from the loo c. c. mark to the three- 

 way stop-cock, /', closing its upper end, is 50 c. c. — making the entire ca- 

 pacity of the tube 160 c. c. The lower end is closed by means of a simple 

 glass stopcock, c. e represents a small cup at the top with marks at 20 and 

 25 c. c. respectively, thus facilitating the measurement of the contained 

 volume of gas at a constant pressure of known amount of water in the cup. 

 /represents an iron stand to which the burette is firmly clamped. 

 d represents a glass tube of wider calibre surrounding the burette, 

 filled with water and serving as a water-jacket to prevent rapid changes 

 in temperature of the gases under examination. 



METHOD OF USING BUNTE S GAS BURETTE. 



The burette is filled with water and the three-way stopcock closing 

 its upper end is so turned as to communicate through it with the external 

 air, or with the vessel containing the air to be analyzed, by means of a 

 short piece of rubber tubing connecting this stopcock with such vessel. 

 By opening the stopcock, closing its lower end, some of the water, say 150 

 c. c, is allowed to flow out, and the air or gas to be analyzed flows in to 

 take its place. When the desired amount of the sample of air has been 

 taken, the lower stopcock is quickly closed and the three-way stopcock is 

 turned half-way round, thus bringing it in communication with the small 

 cup at the top, which should also be filled with water to its 25 c. c. mark. 

 The pressure of the contained air is now equalized and the communication 

 with the cup is closed. A few drops of water always lodge just below the 

 upper stopcock ; these must be dislodged by gently tapping the iron stand 



r II — \ on the floor. In a few minutes the volume of air may be read off. The 



\ ^^\ burette is then connected at its lower end with a Chajinian water pump and 



WiBMMiH^H^^H^ a portion of the water in it is drawn off. The water in the cup is then poured 

 out and about 10 c. c. of a 40 per cent, solution of sodium or potassium hy- 

 droxide poured into it, and in turning the stopcock, this flows in to take the 

 place of the water just removed. The fluid and air in the burette are now 

 gently agitated, at intervals, for five minutes, the cup is again filled with water to the 25 c. c. mark, 

 the stop-cock again oi)ened, and the pressure of the gas equalized. If any of the water flows into 

 the burette more must be poured into the cup to retain the gas under the original pressure of 25 c. c. 

 of water in the cup. This part of the operation requires some care and practice in order to prevent 

 the escape of any of the contents of the burette or the entrance of external air. When the pressure 

 is again e(pialized the volume of gas is again read off, the reduction in volume representing the 

 amount of CO» absorbed, this is readily calculated to the per cent, of the original volume of gas. 



The burette is now once more attached to the Chapman water pump to remove a portion of 

 the fluid in the burette. About 10 c. c. of a 12 per cent, solution of pyrogallic acid is poured into 

 the cup and allowed to flow in. The fluid and gas are gently agitated, at intervals, during five 

 minutes, the pressure equalized as before, the volume of gas read off, .uul the calculations for (). 

 made as before. In most instances N. is the only gas remaining. 



Fig. 6. — liunle's Gas 

 Burette (Xi'o). 



