20 II. METHODS OF INVESTIGATION 



Under illumination, let the residual respiration he changed to n' with 

 corresponding dissociation constant of the carbon monoxide compound K'. 

 Then it follows that: 



the alteration of n to ?;' being due to the additional photodissociation velocity 

 constant 2'. From equations 3 and 4 we get: 



?^ = ^- (5) 



K. z 



If / is the intensity of the light, /3 the molar absorption coefficient, and 

 V the frequency, the photochemical equivalence law of Einstein gives: 



.' = f (6) 



N being Avogadro's number and h Planck's constant. 



For light of the same energy Vjut of different frequencies, v, and Vo cor- 

 responding to wavelengths Xi and X,, we have, attaching the subscripts 1 

 and 2 to the relevant terms: 



Ki — K _ 2i^ ^ j Si V2 _ 01 Xi - . 



K, — K 2, /So VI 02 X2 

 Since Xi and X2 are known, and K, K|, and K2 can be measured by means 

 of equations 2 and 4, the ratio 0\/02 can be found. 



The respiration of the cells is first measured in the dark in oxygen- 

 nitrogen and oxygen-carbon monoxide mixtures of the same oxygen 

 concentration. Thus n is measured and K calculated. The system 

 is then exposed to strong monochromatic light of different wave- 

 lengths and of measured intensity and thus K^ and Ko are obtained. 

 Finally the respiration is measured once more in the dark in order 

 to establish whether any irreversible alteration has occurred. 



By measuring the rate of change of respiration under intermittent 

 light it is possible by varying the periods of illumination and dark- 

 ness, to measure z, the velocity constant of dissociation of the carbon 

 monoxide compound in the dark. Then the absolute values of /8, 

 and the concentration of the catalyst in the cell, can be determined. 



The theory was tested on compounds the absorption spectrum of 

 which could be measured spectrophotometrically, first with carbon 

 monoxide ferrocysteine {51,2) and later with carbon monoxide 

 pyridine hemochrome {1579). In each case the photochemical method 

 gave the correct absorption spectrum. The law of Einstein was found 



