ELEMENTAEY DEMONSTRATIONS 



143 



water in Gr and H protects the pyro solution from the air. F is emptied 

 and refilled through K. The tap on the 

 absorption pipette places either E or F in 

 connection with the gas-burette. 



A sample of expired air is obtained by 

 breathing through the tube into the 

 burette B (Fig. 126). A and B are filled 

 with acidulated water, and B is controlled 

 by a clip. 



The portion of B which lies beyond the 

 clip is squeezed empty of air before it is 

 inserted over the entrance tube of the 

 Haldane gas-burette. The sample is then 

 taken over by lowering the levelling tube 

 and opening the clip. 



The Respiratory Exchange of Gases. 

 Atmospheric air measured dry at C. 

 and at 760 mm. pressure has the following 

 composition : 



o, N 2 . co 2 . 



Atmospheric air, 20 95 79*02 0'03 



Average expired air, 16 '03 79 '59 4 '38 



Expired air is warmed nearly to body 

 temperature, and from 50 to 100 kilo- 

 calories of heat are lost per diem in this 

 way. It is saturated with water vapour. 

 One cubic metre of air takes up 42-2 

 grms. of water at 37 C. The total loss 

 per diem varies from 250 to 500 grms. 

 The heat lost by evaporation of this water 

 equals 145 to 290 kilo-calories. 



One third of the 250 c.c. tidal air is 

 breathed out from the large air tubes at 

 the following expiration, the rest (170 c.c.) mixes by diffusion with 



independent of changes in temperature and barometric pressure during analysis a 

 control tube N is employed. N is connected with the potash solution by means 

 of a T-tube 0. The tap at P makes it possible to render the pressure in N equal 

 to that of the atmosphere. At the beginning of the experiment the potash is 

 adjusted to the mark R by altering S, P being open. P is then closed, and not 

 opened again till the analyses are complete. The barometer and temperature of 

 the water-jacket are read. Each time a reading of the burette is made the potash 

 is brought to the mark R by altering S, and to the mark M by means of the level- 

 ling tube B. As the control tube and the gas-burette are kept moist, variations in 

 the tension of aqueous vapour in the burette are also corrected by the control tube 



FIG. 126. Hempel's burette for col- 

 lecting a sample of expired air. 



