OXYHEMOGLOBIN IN DILUTE SOLUTIONS 139 



To pass now from the method to the results which it achieved ; 

 they are of course subject to a large percentage error, considerably 

 over 20 per cent. 



The results of an experiment at ^H 7-7 and temperature 17-5 are 

 as follows : 



The times are measured from the earHest obtainable reading. It 

 will be noted that the time taken to reach half-completion is less 

 than one seven-hundredth of a second. 



The value of k' for the interval t = 0—0-00184 sec. is 106, and 

 for the interval t^ 0-00184 — 0-00370 sec. is 157; the mean being 132. 



Our interest in the above experiment hes in the fact that the 

 velocity constant in the later portion of the reaction is not less than 

 in the earUer portion. 



A second experiment, carried out on similar hnes, gave results which 

 varied from 120 to 130. Taking the mean of observations made under 

 those particular conditions of temperature and hydrogen-ion con- 

 centration the value for k' averages out at 128 plus or minus over 

 10 per cent. 



Though particular pains were taken in the regulation of the 

 hydrogen-ion concentration by means of a buffer and in the 

 observation of the temperature, it is noteworthy that the velocity 

 of the reaction 



Hb + O2 ^- HbOa 



is almost independent of changes in either of the factors mentioned. 

 It has been observed above that the velocity constant of the re- 

 action is the same over the whole of its course. This does not mean 

 that the rate of formation of oxyhsemoglobin is the same at the end 

 of the reaction as at the commencement, and indeed Fig. 41 shows 

 it to be otherwise. Towards the end of the reaction less oxyhsemo- 

 globin is being formed in a given interval of time than at the com- 

 mencement. There are two reasons for this. The first is that the 

 formation of oxyhsemoglobin at any moment is proportional to the 

 products of the concentrations of reduced hsemoglobin and oxygen, 

 which are ever becoming diminishing quantities. The second is that 

 as oxyhsemoglobin is present in increasing amounts it tends more 

 and more to break up and set the reaction in the opposite direction. 

 The measurement would in theory be much easier if the oxyhsemo- 

 globin immediately on formation were removed from the system. It 

 has not been found possible to do this, and therefore the eflfect of the 



