ELEMENTARY EXPERIMENTAL PHYSIOLOGY 



191 



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 



Pio. 187.^-Ferricyanide method of estimating the oxygen capacity of blood. 



the barometer are taken and the gas is reduced to its volume at 

 and 700 mm. 



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

 cyanide 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. Oxygen 

 is rendered available for the formation of methaemoglobin after the 

 oxygen of the oxyhaemoglobin has been liberated. 



Hb/ | + 4Na 3 (Cy 6 Fe) + 4NaHC0 3 = 0. 2 + Hb<Q 



+ 4Na 4 (Cy 6 Fe) + 4C0 2 + 2H 2 O. 



/ O 



In this case Hb/ | represents oxyhaemoglobin, and Hb^^ 



^O 



methaemoglobin, for it is held that the oxygen atoms are united 

 together in oxyhaemoglobin but not in methaemoglobin. 



