CHAPTER IX 



THE MOLECULAR WEIGHT OF HAEMOGLOBIN 



_r ROM the chemist's point of view the molecular weight of haemo- 

 globin is one of those things which is of first importance. Yet it has 

 proved most illusive. Needless to say almost every worker has been 

 anxious to determine it, but the determination has till recently 

 proved a veritable will-o'-the-wisp and even now the subject is 

 surrounded with many difficulties. The thermal method at one time 

 held out great hopes. The perusal of Chapters xvi and xvn shows 

 to how small an extent these hopes have been realised. There is no 

 question of vapour pressure. We turn therefore to the osmotic 

 pressure. We know as a starting-point that the least possible 

 molecular weight — that which contains 56 grams of iron — would be 

 somewhere around 16,700. If then we caU the molecular weight 

 (16,700)„, what is the value of n? 



I may pass rather rapidly over the work of Hiifner and Gansser(i), 

 who came to the conclusion that the osmotic pressure of a 1 per cent, 

 solution of haemoglobin would be 10 mm. of mercury — a result which 

 would give a value oi n = 1. By what happy accident Hiifner and 

 Gansser arrived at this result is likely to remain a mystery. Waymouth 

 Reid(2), in a research which is too little quoted, concluded that 3 

 was the nearest whole number to his determinations of n. Roaf (3> 

 made the material but rather depressing discovery that n might 

 appear to be almost anything — ^less than unity, for instance — ac- 

 cording to the circumstances in which the measurements were made. 

 It has remained for Adair (4) to reduce to some sort of order the 

 apparently chaotic readings which were found. The possibilities of 

 adsorbed salts, of variable ionisation of the hydrogen or sodium ions,^ 

 of membrane potentials, of polymerisation of the haemoglobin, of 

 the onset of putrefaction, of the attainment of a true equilibrium, etc., 

 all had to be taken into account. Take the last two considerations, 

 the avoidance of putrefactive changes and the attainment of equi- 

 Ubrium. In ordinary circumstances it proved quite impossible to 

 complete a measurement in a time so short as to guarantee freedom 

 from putrefaction. This difficulty was overcome by working at — 0-6° C. , 

 at which temperature a haemoglobin solution remains good indefinitely. 



