PRACTICAL EXERCISES 293 



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 ef 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 hydroxide, 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 hydroxide may also be added, if the 

 piece first introduced is entirely dissolved. Shake as described in (i), 



FIG. 133. HALDANE'S APPARATUS FOR MEASURING THE QUANTITY OF C(X AND 

 AQUEOUS VAPOUR GIVEN OFF BV AN ANIMAL. 



A, chamber into which the animal is put ; i and 4, Woulff's bottles filled with 

 soda-lime to absorb carbon dioxide ; 2, 3, and 5, Woulff's bottles filled with 

 pumice-stone soaked in sulphuric acid to absorb watery vapour ; B, glass bell-jar 

 suspended in water, by means of which the negative pressure is known ; P, water- 

 pump which sucks air through the apparatus ; i and 2 are simply for absorbing 

 the carbon dioxide and water of the ingoing air. 



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. 



10. Estimation of the Quantity of Water and of Carbon Dioxide 



