198 



ESSENTIALS OF CHEMICAL PHYSIOLOGY 



of the apparatus and weighed, the clips, a and 6, being tightly closed. Blood 

 is then introduced into it by connecting the tube with the clip a on it to a 

 cannula filled with blood inserted in an artery or vein of a living animal. 

 Enough blood is withdrawn to fill about half of one of the bulbs. This is 

 defibrinated by shaking it with the few drops of mercury left in the bulb. 

 It is then weighed again ; the increase of weight gives the amount of blood 

 which is being investigated. B.B. is then once more attached to the rest of 

 the apparatus, hanging downwards, as in the side drawing in fig. 80, and 



the blood gases boiled off ; these pass into 



<?, which has been made a vacuum ; and 



then, by raising R again, the mercury 



I rises in d, pushing the gases in front of 



^ it through the tube e (the stopcock being 



f turned in the proper direction) into the 



eudiometer, E, which has been filled with, 



and placed over, mercury. The gas can 



then be measured and analysed. 



ANALYSIS OF GASES 



Waller's modification of Zuntz's more 

 complete apparatus will be found very 

 useful in performing gas analysis, say of 

 the expired air or blood gases : a 100 c.c. 

 measuring-tube graduated in tenths of a 

 cubic centimetre between 75 and 100 ; a 

 filling bulb and two gas pipettes are con- 

 nected up as in the diagram. 



It is first charged with acidulated 

 water up to the zero mark by raising 

 the filling bulb A, tap 1 being open. It 

 is then filled with 100 c.c. of expired 

 air, the filling bulb being lowered till 

 the fluid in the tube has fallen to the 

 100 mark. Tap 1 is now closed. The 

 amount of carbonic acid in the expired 

 air is next ascertained ; tap 2 is opened, 

 and the air is expelled into the gas pipette 

 B containing strong caustic potash solution by raising the filling bulb until the 

 fluid has risen to the zero mark of the measuring tube. Tap 2 is closed, 

 and the air left in the gas pipette for a few minutes, during which the 

 carbonic acid is absorbed by the potash. Tap 2 is then opened and the air 

 drawn back into the measuring tube by lowering the filhng bulb. The 

 volume of air (minus the carbonic acid) is read, the filling bulb being 

 adjusted so that its contents are at the same level as the fluid in the 

 measuring tube. The amount of oxygen is next ascertained in a precisely 

 similar manner by sending the air into the other gas pipette, which contains 

 sticks of phosphorus in water, and measuring the loss of volume (due to 

 absorption /Sf.,p^jg^|||\rn 'the air when drawn back into the tube. The 

 remaining gas is nitrogen. 



A 



Fig. 81. — Waller's apparatus for gas 



analysis. 



