34 Chapter III 



In the present chapter we have established a value for the heat 

 of molecular combination of oxyhaemogiobin : this involves the idea 

 that K is constant at any temperature but not the assumption that 

 haemoglobin is necessarily Hbj rather than Hb 2 or Hb 3 , i.e. that 

 its molecular weight is approximately 16,700 rather than 33,400 or 

 50,100. We are therefore in this position ; osmotic pressure experi- 

 ments have yielded all of these values as well as many others, our 

 own results hitherto lean to the first, do not exclude the second but 

 seem to exclude the third. Can we use the heat of formation of 

 a gram-molecule of oxyhaemogiobin, Hb n O 2w , to decide the question? 

 We can. For it proved possible to determine the actual amount of 

 heat developed when one gram of haemoglobin unites with oxygen : 

 calling this quantity H, then the molecular weight of the molecule 



We need hardly remind the reader that as compared with the 

 accuracy of chemical analysis this determination may be rather 

 rough. If, for instance, we obtain a value for the molecular weight 

 of say 13,000 or 20,000 we might in either case regard n as unity. 

 In practice the observation of the heat of combination of oxygen 

 with haemoglobin proved much simpler than we had expected. The 

 haemoglobin was reduced in a vacuum pump and allowed to run 

 directly from the pump into a cylindrical De war's flask, the surface 

 of the solution being protected from air by a coating of neutral olive 

 oil. A sample of haemoglobin solution was analysed and oxygen was 

 then bubbled through the fluid for a given time about 5 minutes 

 at the end of which a second sample was withdrawn and analysed. 

 The rise of temperature was observed with a simple Beckmann's 

 thermometer. The necessary corrections were made for the amount 

 of heat which the solution acquired if standing by itself, and so 

 forth, and when this had been done we arrived at the rise of tem- 

 perature in the haemoglobin solution as the result of the oxidation. 

 We have therefore two measurements: (1) the amount of heat 

 produced by the oxidation and (2) the amount of oxygen absorbed. 

 On the assumption, the correctness of which has been shown in 

 Chapter I, that each gram of haemoglobin unites Avith 1'34 c.c. of 

 oxygen we may calculate the number of grams of haemoglobin which 

 have been oxidised ; we therefore have all the data which we re- 

 quire. The result of our observations was that H, the quantity 

 of heat evolved when 1 gram of haemoglobin unites with oxygen, is 



