The Intermediate Compound Hypothesis 



the case of combination and k is only constant below y = 70 per cent 

 in the case of dissociation. Above these respective ranges, k' tends to 

 rise quite appreciably and k to fall very appreciably (see pp 70 — 72). 

 For average sheep haemoglobin at p\\ 9-3, 19°C, it is found that 

 k = 12 and k' = 6*5 when 2 concentrations are measured in mm Hg 

 of partial pressure of dissolved 2 (so as to be uniform with the units 

 used in the dissociation curve calculations). 



Case A of the previous section assumes that the first three inter- 

 mediate reactions are governed by statistical relations, but that the 

 fourth reaction shows large interaction. 



Accordingly 



ky! : k«' : k 3 ' : : 4 : 3 : 2 



I * _ * 3 * ■ " * 



K x :K 2 :K 3 :: 1 :| r^and/^ =0-32 



The values of & 4 ' and & 4 remain to be settled, subject of course to the 

 condition that k^'/k^ = K^ (= 8-8 in the present instance). The 

 investigation now proceeds as follows : — 



First the question of the combination velocity is tackled. The 

 relationship between y and t (on the basis of equation (3)) is worked 

 out for a series of cases, in all of which k x = 4, k 2 ' — 3, k 3 = 2 but 

 kl is given the values of 1-0, (i.e. the fourth reaction also ' statistical ') 

 6-0, 20-0, 36-0, 440 and co . For fc 4 ' = 20 and above, the values of y 

 are found to be the same to within 0-4 per cent at all times, and the 

 value of k', as calculated for various intervals, ranges from 1-07 (from 

 y = to y = 35) to 1-42 (from y = to y = 80). For /c 4 ' = 1, the 

 calculated value of k' remains equal to 1-0 over the whole range, and 

 for 1 < k\ < 20, k' shows a smaller rising trend than at &Y = 20. 

 To account for the observed value of k' = 6-5 from y = to y = 50 

 per cent we therefore take ^' = 6x4= 24, k 2 ' — 18, k z ' = 12 and 

 for the moment fc 4 ' must be left undecided, since, as just shown, it 

 can be varied over a very wide range without affecting the calculation 

 of k' appreciably. 



Next, the relation between y and / is worked out for the dissociation 

 velocity for a series of cases in all of which k 4 = 1 and k s : k 2 : k x : :3 

 : 2: 1, but k x is given the values 0-25 (the complete ' statistical ' case), 

 2-0, 3-0, 5-0, 9-0 and co . The values of k are calculated for various 

 intervals over the range of saturation from y = 100 per cent to y = 5 

 per cent. For k x -+ co , it is found that k = 1 over the whole range, i.e. 

 the reaction is kinetically unimolecular from start to finish. For 

 k x = 9, it is found that k = 0-59 (for y = 100 per cent to y = 90 per 

 cent) and = 0-93 (for y = 90 per cent to 77 per cent), whilst from 

 y = 11 per cent to y = per cent, k = 1 throughout. For k x = 5, 



91 



