Some Photochemical Experiments with Pure Chlorophyll. 353 



At the end of the experiment the gas was analysed in a Haldane gas 

 analysis apparatus, and was found to consist of 100 per cent, carbon dioxide. 



(c) Oxygen. 



It is well known that chlorophyll bleaches rapidly in air or in 

 oxygen when exposed to light. This was also the case in our own experi- 

 ments with a colloidal solution of chlorophyll. The bleaching is preceded by 

 -a change in colour from green to yellow-green or brown-green, similar to that 

 produced when carbon dioxide was used. Spectroscopic examination 

 indicates the presence of phseophytin. It seems reasonable to suppose 

 that an acid substance is produced during the bleaching, which reacts with 

 the chlorophyll not yet bleached, giving phaeophytin in the usual way. If a 

 small quantity of alkali is added the brown-coloured stage is omitted and 

 bleaching accelerated. 



Formaldehyde Test. — Formaldehyde is not produced in any quantity 

 during the bleaching of chlorophyll in oxygen, but, after bleaching is 

 complete, formaldehyde is formed in amounts which can be easily estimated. 

 We have made estimations of the quantity of formaldehyde produced by the 

 action of oxygen on chlorophyll after various times of exposure to light, 

 using Schryver's method for estimating small quantities (Schryver, 6, 7). 

 The results of these experiments are summarised in the accompanying 

 Table, and are exhibited graphically in the curves shown in fig. 2. 



We have already mentioned the production of formaldehyde from alcohol 

 exposed in quartz vessels. The curve C shows how large is the quantity of 

 formaldehyde produced when this substance is present. In this case a 

 chlorophyll sol (with traces of alcohol) was exposed to light in a large 

 quartz vessel, and samples examined from time to time. In the case of 

 glass vessels, the presence of traces of ethyl alcohol makes no difference 

 in the amount of formaldehyde produced, as is shown by a comparison of 

 curves A and D. 



The small quantities of formaldehyde obtained before bleaching is complete 

 are no doubt produced from the part of the chlorophyll already bleached. 



It seems reasonable to suggest that the production of formaldehyde is due 

 to the oxidation of the methyl or phytyl ester groups of the chlorophyll 

 molecule. According to Willstatter, the alcohol phytol is a primary alcohol 

 of formula C20H39OH, whose structure may be represented thus: — 



CH 3 — CH— CH— CH— CH— CH— CH— CH— C=C— CH 2 OH 



I I I I I I I I I 

 OH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 UH 3 CH 3 



In the oxidation and breaking down of this alcohol, it is evident that 



