12 



Prof. A. J. Ewart. 



38 per cent, in volume to 80 c.e. It contained 79 7 c.c. of carbon dioxide 

 and - 3 c.c. of nitrogen* On adding cold alcohol to the film it formed a 

 pure yellow solution of xanthophyll, leaving a slight white insoluble portion 

 on the glass. The water from the tube contained no perceptible amount of 

 formaldehyde or of reducing sugar. 



A similar experiment was repeated with a large tube with exactly similar 

 results, the residual gas being less in amount and consisting of 99 - 8 CO2 and 

 0*2 per cent, nitrogen. The yellow film when dried weighed 044 grm., 

 whereas the original chlorophyll weighed - 34 grm. 



Evidently, therefore, chlorophyll, when exposed to sunlight in the presence 

 of carbon dioxide and water, increases in weight and forms xanthophyll and a 

 colourless waxy solid, but liberates no free oxygen. 



The same change takes place in darkness, but more slowly, and in the same 

 way the oxidation of chlorophyll takes place slowly in darkness, although it 

 is very greatly accelerated by exposure to light. 



In a second experiment a film of dry chlorophyll weighing 0174 grm. 

 was exposed to air in darkness for 10 days. It lost 0'006 grm. of weight, 

 and, during the next seven days, - 004 grm. The next week it was kept 

 in a mixture of dry air and carbon dioxide. It lost a further - 003 grm. 

 in weight but was still quite green. During the next week it was kept still 

 in darkness, but in water saturated with CO2. The film became dull, 

 contained mainly xanthophyll with a trace of chlorophyll at one point only, 

 and on drying showed a bright yellow colour and weighed - 165 grm. 

 The water contained no perceptible formaldehyde, and, although it gave no 

 distinct reduction with Fehling's test, left a residue of - 052 grm. In spite 

 of its long exposure, therefore, in the presence of an excess of C0 2 dissolved 

 in water, the chlorophyll combined with carbon dioxide forming xanthophyll 

 and a colourless, waxy residue dissolving readily in petrol ether. 



Water alone has no effect on chlorophyll. Thus, films kept for one week 

 in darkness in water deprived of all carbon dioxide were still quite green and 

 apparently unaltered. On keeping the water saturated with carbon dioxide, 

 the films after two weeks' darkness became dull yellow, and gave a pure 

 yellow solution of xanthophyll soluble in cold alcohol, and leaving a colour- 

 less, waxy skin, soluble in petrol ether. This waxy material in all cases 

 prevents the xanthophyll from dissolving in the water, which remains 

 colourless, but when the xanthophyll is isolated it has the same properties 

 as that obtained directly in chlorophyll extraction. 



If oxygen is present as well as carbon dioxide, the water in the beaker 



* This nitrogen may have come from the chlorophyll, but more probably remained 

 dissolved in the water when the tube was sealed. 



