6 



Prof. A. J. Ewart. 



surface, which is almost impermeable to oxygen. Thus, in one case, 

 - 73 grm. of dry chlorophyll (petrol-ether extract), after one week's 

 exposure in dry C0 2 -free air, was partly bleached and weighed 04 grm. 

 For full bleaching four months' exposure was necessary, the weight then 

 being 02 grm., and after extraction with water and drying being - 13 grm. 

 of white insoluble waxy solid. 



Filter paper saturated with chlorophyll is unsuitable for exact experiments, 

 and in addition moist filter paper after long exposure to sunlight may develop 

 appreciable traces of reducing sugar, which can be extracted by water. Hence 

 thin sheets of glass and mica were used on which solutions of chlorophyll in 

 petrol ether were allowed to evaporate and form even films. For certain 

 experiments thin-walled glass tubes 6 feet in length were employed. 



To determine the influence of carbon dioxide on oxidation, dry films were 

 exposed to sunlight in nearly dry air with and without carbon dioxide. In 

 the presence of a little carbon dioxide the bleaching appeared to be accelerated 

 and - 44 and 04:53 grm. of chlorophyll left - 198 and 0-22 grm. of white 

 residue, whereas in the absence of carbon dioxide 0"462 aud 043 grm. of 

 chlorophyll left 0*145 and - 123 grm. of dry white residue. This residue 

 contains a little matter soluble in water and this is slightly more abundant 

 in the films oxidised in the presence of carbon dioxide and the weight of the 

 residue is greater. Dry films oxidised in dry air contain relatively little 

 matter soluble in water. 



Tubes were then lined with dry chlorophyll, filled with pure dry nitrogen 

 and pure dry carbon dioxide and exposed to light for periods of 1 to 8 weeks. 

 All remained green, but the films in CO2 become a little more yellowish, and 

 a little of the CO2 disappeared. No oxygen or formaldehyde was formed. 

 Similar tubes filled with dry air were exposed until bleaching ceased. The 

 residual gas contained no oxygen but 2"2 per cent, of gas removable b} T potash. 

 Further tests showed that this gas consisted wholly of formaldehyde gas. 



Additional evidence that chlorophyll is able slowly to combine with CO2 

 during its oxidation was obtained by exposing thick films to sunlight in air 

 containing a little moisture and carbon dioxide until fully bleached, which 

 took just over a month. In one case 0*8 grm. left a dry bleached residue of 

 - 785 grm. dry weight, whereas in pure air the bleaching was much slower 

 and a similar quantity lost 68 per cent, by weight. A portion of this may be 

 due to the fact that in pure dry air a slow loss of weight by photo-oxidation 

 continues for some time in the bleached residues, whereas if the film is thin 

 and the oxidation rapid in moist air, there may be little or no loss of weight 

 by the time the film is bleached, the oxygen absorbed weighing nearly as 

 much as the gas lost. Thus 049 grm. of chlorophyll spread out in a thin film 



