144 



PRACTICAL PHYSIOLOGY 



The ammonia prevents the evolution of carbon dioxide and the 

 distilled water lakes the corpuscles. The mixture is thoroughly 

 shaken to complete the laking. Into the tube B are placed 4 c.c. 

 of a freshly saturated solution of potassium ferricyanide. The 

 rubber cork is inserted into the bottle A and the water in the 

 burette is brought to a level close to the top by opening the tap 

 and -raising the levelling tube. The tap is closed and the reading 

 of the burette taken. The water gauge attached to the temperature 

 and pressure control tube is adjusted by sliding the rubber tubing 

 backwards or forwards on the glass tube D. 



The bottle A is tilted so that the ferricyanide in B escapes and 



FIG. 139. Ferricyanide method of estimating the oxygen capacity 



of blood. 



the mixture is shaken until the evolution of gas has ceased. If the 

 pressure gauge indicates an alteration in the temperature of the 

 water this is adjusted by the addition of cold or warm water to 

 the bath. After allowing the temperature to become constant and 

 levelling the water in the burette and levelling tube, the amount 

 of gas is read. The temperature of the water surrounding the 

 burette and the height of the barometer are taken and the gas is 

 reduced to its volume at and 760 mm. 



The chemistry of the process appears to be as follows : The 

 ferricyanide is reduced to ferrocyanide, for if ferricyanide be added 

 to laked blood it will be found that the solution gives with ferric 

 chloride the blue colour which indicates the presence of ferrocyanide. 



