PRACTICAL EXERCISES 275 



(3) Repeat (i) with the tube connected to the mouth by a glass 

 tube held between the lips, and the nostrils open. 



(4) Repeat (2) with the tube in the mouth and nostrils closed. 



5. Determination of Carbon Dioxide and Oxygen in Inspired and 

 Expired Air (i) Estimation of Carbon Dioxide. Fill a burette 

 with water, and close the pinchcock on the rubber tube. Immerse 

 the wide end of the burette in a large vessel of water, and fill it with 

 carbon dioxide by putting into it below the water a tube connected 

 with a bottle in which carbon dioxide is being evolved by the action 

 of hydrochloric acid on marble chips. See that gas has been coming 

 off freely from the bottle for a little time before the tube is put under 

 the burette. Do not fill the burette with gas beyond the graduated 

 part. Hold the burette in the vertical position, its mouth being still 

 immersed, make the level of the water the same inside and outside^ 

 and read off the meniscus. Then introduce a piece of stick sodium 

 hydrate, close the burette with a finger or the palm of the hand, lift 

 it out of the water, and by a sort of see-saw movement shake the 

 sodium hydrate repeatedly from end to end of it. Again immerse 

 the burette, and read the level of the meniscus. Most of the gas 

 will be absorbed. Repeat the shaking. If the reading is still the 

 same, absorption is now complete. 



(2) Estimation of Oxygen (Analysis of Inspired Air). Fill the 

 burette with the air of the laboratory. Open the pinchcock, and 

 immerse the wide end of the burette till the water reaches the gradua- 

 tion. Then close the cock, and read off the meniscus. Introduce a 

 piece of sodium hydrate, and proceed as in (i). Notice that there 

 is no appreciable absorption. (This method is not suitable for the 

 measurement of the small quantity of carbon dioxide in ordinary 

 air.) Now introduce, under water, some pyrogallic acid. This can 

 be done conveniently by wrapping up some of the crystals in thin 

 paper so as to form a kind of small cigarette, which is pushed up into 

 the burette. A little more sodium hydrate may also be added, if the 

 piece first introduced is entirely dissolved. Shake as described in 

 (i), till no more absorption takes place. Then read off the meniscus 

 again (always making the level the same inside and outside the burette). 

 The difference in the two readings gives the amount of oxygen present. 

 What remains in the burette is nitrogen (and a little argon). Its 

 amount is, of course, equal to the reading of the burette, plus the 

 capacity of the ungraduated part at the narrow end of the burette, 

 which must be determined once for all by a separate measurement. 



(3) Analysis of Expired Air. (a) Fill the spirometer with water, 

 breathe into it several times in your ordinary way, but be careful not 

 to inspire any air from the spirometer ; then fill the burette with the 

 expired air from it. Or simply expire several times through the 

 burette, seeing that none of the inspired air comes through it. 

 Determine, as in (i) and (2), the percentage amount of carbon 

 dioxide, oxygen and nitrogen, (b) Repeat (a) with air expired 

 after the lungs have been thoroughly ventilated by taking a number 

 of deep breaths in succession, and determine whether there is any 

 difference in the percentage amounts. 



