CH. XXIV.] GAS ANALYSIS 385 



positions, the stopcock cuts off all communication from d to all parts of the apparatus 

 above it ; d is connected by tubing to a receiver, R, which can be raised or lowered 

 at will. At first the whole apparatus is filled with mercury, R being raised. Then, 

 a being closed, R is lowered, and when it is more than the height of the barometer 

 (30 inches) below the top of B. B. the mercury falls and leaves the blood bulb empty ; 

 by lowering R still further, d can also be rendered a vacuum. A few drops of 

 mercury should be left behind in B.B. B.B. is then detached from the rest 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 with- 

 drawn to fill about half of one of the* bulbs. This is defibrinated by shaking it with 

 the few drops of mercury left in the bulbs. 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. 338, and the blood gases boiled off; these pass into d, which has 

 been made a vacuum ; and then by raising R again, the mercury rises in d, pushing 

 the gases in front of it, through the tube, e (the stopcock being 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. 



Gas analysis. There are many pieces of apparatus devised for this purpose. 

 In physiology, however, we have generally to deal with only three gases, oxygen, 

 nitrogen, and carbonic acid. 



Waller's modification of Zuntz's more complete apparatus will be found very 

 useful in performing gas analysis, say, of the expired air, or of the blood gases. 

 A 1 00 c.c. measuring-tube graduated in tenths of a cubic centimetre between 75 

 and 100 ; a filling bulb (A) and two gas pipettes are connected up as in the diagram 

 (fig. 339). 



It is first charged with acidulated water up to the zero mark by raising the 

 filling bulb, 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 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 filling 

 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 of oxygen) in the air 

 when drawn back into the tube. 



