THE INDIVIDUAL GROUPS OF PROTEINS 501 



(2) Barcroft and Haldanes Method. 



Barcroft and Haldane in 1902 described a method for estimating the 

 oxygen in small quantities of blood (i c.c.). The apparatus required is shown 

 in Fig. 67. 



It consists of two bottles of about 25 c.c. capacity with glass stoppers 

 prolonged into the interior in the form of a cup. They are connected by 

 india-rubber tubing to pressure gauges upon each of which there is a 3-way 

 tap connecting the bottle and manometer to the air. The bottles and gauges 

 are fixed upon a stand so that the two bottles can be immersed together in 

 the same bath of water and thus have the same temperature. One of the 



FIG. 67. (From J. Physiol., 28, 233, Cambridge University Press.) 



bottles is not used and simply serves as a control for recording temperature 

 changes, etc. The blood is placed in ammonia solution in one of the bottles 

 and ferricyanide in the cup. On upsetting the ferricyanide into the blood the 

 volume of gas evolved causes a change of level in the pressure gauge which 

 is observed. The volume of gas is measured by the change of pressure. This 

 is effected by the use of rubber tubing at the base of the gauges, which can 

 be -compressed by a screw. Before the experiment the levels of the two 

 gauges are set at the zero point with the taps open to the air and therefore at 

 atmospheric pressure. The tap of the bottle in which the experiment is 

 performed is shut to the air, the ferricyanide is upset, and when the temperature 

 is the same throughout, the levels of both gauges are brought to the original 

 levels in the" limbs attached to the bottles by altering the pressure of the screws 



