214 



METHODS OF GAS ANALYSIS. 



[BOOK i. 



provided with two scales placed side by side, one of which indicates volumes in 

 tenths of a cubic centimetre, the other is divided into millimetres. Further, 

 these tubes are very much constricted at their upper part, so that exceedingly 

 minute quantities of gas can be very accurately measured; this device 

 renders the tubes of special value in the determination of the gases of the 

 blood, as the volume of nitrogen which has to be read off is always very 

 small. 



We shall suppose, then, that the experimenter has, by employing 

 Alvergniat's pump, collected the gases given off from a known volume of 

 the blood which he is analyzing, in such a graduated tube, the walls of 

 which have been moistened by a drop of water. He now transfers the 



FIG. 49. WELL-SHAPED PNEUMATIC 

 TROUGH FOB MERCURY. (Scale about 



\J 



FIG. 50. PIPETTE WITH BULB, 

 FOR INTRODUCING LIQUID REAGENTS 

 INTO ABSORPTION TUBES STANDING 

 OVER MERCURY. (Scale about ^.) 



tube with its contents to the mercurial trough having the form shewn in 

 Pig. 49 ; the transference being effected by means of the iron spoon shewn 

 in Fig. 48. The tube is then fixed in a clamp and plunged into the mercury 

 so that the level of the metal inside and outside the tube is exactly the 

 same; it should be left for an hour, and a second observation made to see 

 whether the level is still the same. If any change has occurred the tube 

 is again adjusted and the volume of the gas is read off, either by the 

 unaided eye, or still better by means of a telescope magnifying a few- 

 diameters and situated at a distance of a few feet from the tube. 



The observer then reads the thermometer and barometer, and thus 

 obtains the data for calculating the total quantity of gas given off by the 

 volume of blood which he has analyzed. 



With the aid of a pipette such as is shewn in Fig. 50, the observer 

 now throws up into the tube about half a cubic centimetre of solution 



