502 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



on the rubber tubes. The liquid in the gauge in the other limbs rises. The 

 difference in level between the two limbs gives the increase of pressure due 

 to the evolution of oxygen. 



The pressure gauges are filled with water; at 15 the normal barometric 

 pressure equals 10,340 mm. of water. 



The volume of oxygen evolved at 760 mm. 



volume of air in the apparatus x corrected reading of gauge 



10340 



If the bottle had a capacity of 23-35 c - c - a nd the fluids used had a volume 

 of 275 c.c., then the volume of air is 20*6 c.c. 



Supposing the gauge to read 100 mm. the oxygen evolved is 



100 



20'6 X - - = '201 C.C. 



10340 



This volume is corrected to o. 



The capacity of the bottle is ascertained by weighing it empty and full 

 of water ; the capacity of the connections by adjusting the gauge to zero 

 and raising the pressure to a definite amount (i) with the vessel attached, (2) 

 with a stopper in place of the bottle. 



Capacity of bottle : capacity of connecting tubes = 

 Change of volume in (i) : change of volume in (2). 



This method has been improved and modified by Brodie and by Barcroft 

 and his co-workers. In its original form it is seldom used, but the principle 

 of using pressure change to determine the volume is maintained. 



(3) Barcrofts Method. 



The apparatus in its most convenient form for estimating oxygen in i c.c. 



of blood was illustrated in 1910 and again 

 in 1911 1 (Fig. 68). It consists of two 

 glass egjj-snaped bottles fused to a pres- 

 sure gauge, which at the top is provided 

 with 3-ways taps and at its base is con- 

 nected by a wider piece of tubing by 

 means of a cork, A, to a i c.c. pipette. 

 X, graduated in T J a ths. To the pipette 

 is attached a piece of rubber tubing, C, 

 upon which a screw can be tightened or 

 relaxed. A piece of glass tubing, B, is 

 put into the rubber tubing ; it is sealed 

 when the level of the liquid in the limbs 

 of the gauge has been adjusted. The 

 bottles are furnished with hollow stoppers 

 inside which there are small tubes. These 

 are to contain the ferricyanide solution. 

 They are open at the side of the stopper, 

 but the contents do not flow out until 

 the opening is in contact with a small 

 ampulla on the neck of the flask. The 

 bottles have a capacity of about 30 c.c. 

 and the bore of the gauge is i mm. 



The gauge is filled with clove oil (10,000 mm. = 760 mm. of mercury) which 

 is introduced at the wide part of the gauge, A, nearly filling it. The cork carry- 

 ing the pipette, X,is inserted avoiding air bubbles and the oil ascends in the limbs 



1 J. Physiol.,42, 513. 





3k-:--'-"? 



AIMD& TATLOCK 

 (LONDON 



FIG. 68. 



