CARBON DIOXIDE AND OXYGEN 



3 11 



cavity of the mouth, closing the lips firmly about it, leaving the pharyngeal 

 muscles relaxed. Note the variations in pressure at the height of ordinary 

 inspiration and expiration, with the nasal passages open. Repeat with 

 forced inspiration and expiration, close the nasal passages, and make the 

 maximal expiratory and inspiratory effort. The manometer may be ad- 

 justed to write on the smoked paper or one may read the variations directly 

 from the manometer schedule, in which case it facilitates the reading if one 

 clamps the rubber tube at the moment the reading is desired. 



7. Demonstration of Carbon Dioxide in Expired Air. Arrange 

 two flasks, as in figure 246, filling each one-third full of baryta-water or 

 lime-water. Close the lips around the mouthpiece of the apparatus and 

 inhale and exhale the air through it; close the nostrils if necessary. The 



FIG. 246. Apparatus for Demonstrating Excess of CO 2 in Expired Air. Flasks filled with 



lime-water. 



inspired air will come through a, the expired air out through b. The baryta 

 water in b will quickly become clouded with a white precipitate of calcium 

 carbonate while that in a will remain clear or only very slightly clouded, 

 showing the excess of carbon dioxide in expired air. 



8. Quantitative Determination of Carbon Dioxide and Oxygen in 

 Inspired Air and in Expired Air, by Hempel's Method. Inspired Air. 

 Fill a gas buret, see figure 236, with water and close the pinch-cock. Fill 

 it with air taken outside the laboratory. Measure the volume of gas con- 

 tained at the ordinary temperature and barometric pressure of the labora- 

 tory. Connect with a potash pipet, drive the air over into the bulb of the 

 pipet, shake it up until all the carbon dioxide is absorbed. Draw the air 

 back into the buret and measure. The amount of carbon dioxide in the 

 external air is usually so small that it is difficult to measure by this method. 

 Now connect the buret with a pipet containing pyrogallic acid, run the air 

 over into the pyrogallic-acid bulb and shake up thoroughly until no further 

 gas is absorbed, then remeasure the excess in the buret. The loss in volume 

 is due to the absorption of oxygen; the air remaining in the buret is nitrogen. 

 Compute in percentage the amounts of carbon dioxide, oxygen, and nitrogen 

 from the results of your test. 



