THE CHEMISTRY OF RESPIRATION 



1105 



It is determined by finding what rise of pressure in the apparatus is produced by 

 the liberation of a known volume of oxygen from hydrogen peroxide, which is placed in 

 the bottle, the liberation being effected by the addition of potassium. 



To determine, the oxygen capacity of a sample of blood. Place 2 c.c. of ammonia solution 

 (made by adding 4 c.c. of strong NH 3 to a litre of water) in one of the bottles and add 

 1 c.c. of blood. Thoroughly lake the blood. Rub vaseline on the large and small stoppers. 

 Put 0*2 c.c. of a saturated solution of potassium ferricyanide in the sma.ll tube in 

 the stopper of the bottle containing the blood (this is best done with a fine pipette 

 which goes down this tube). Insert the small stopper. Place the apparatus on the 

 side of a large water bath (such as a pail) with both taps open. In about five minutes close 

 the tap on the side of the blood and rotate the bottle on the stopper till the ferricyanide 

 trickles into the laked blood. Shake thoroughly, replace in the bath, and repeat this 

 several times till a constant difference of level is obtained. By means of the screw clamp 



FIG. 506. Barcroft's blood-gas apparatus. 

 A, for 1 c.c.; B, for O'l c.c. blood. 



bring the column of oil on the side of the blood to its original level, and then measure 

 the difference of level between the two sides. Let this difference of level be y mm. ; 

 let p be the height of the barometer in millimetres of clove oil, and x the volume of 



/V N 

 oxygen given off in cubic millimetres ; then x = y ( J. Except in the most exact work 



y 



p may be taken as 10,000 mm., in which case the expression may be determined once 



for all and called C, the constant of the apparatus : then x y X C. 



To determine the gaseous contents of a given blood. If we wish to determine the actual 

 amount of oxygen as oxyhsemoglobin in the sample, the blood must be carefully intro- 

 duced so as to lie below the ammonia and not to come in contact with the air. The 

 stopper is then replaced in the bottle and immersed in the bath, with both taps open 

 until it has attained a constant temperature. The tap is then closed and the height of 

 the column of oil noted. The blood is then laked by rotating the apparatus, and after 

 allowing five minutes for complete laking the ferricyanide is run in. The rest of the 

 determination is carried out as above. 



The carbon dioxide may be determined hi the same sample of blood by adding 

 tartaric acid in the same way as potassium ferricyanide was previously added. It is 

 necessary always to determine the oxygen before the carbon dioxide, since the mere 



70 



