Some Photochemical Experiments with Pure Chlorophyll. 351 



of carbon dioxide cannot be employed. Accordingly a pressure of 380 mm.. 

 CO2 + 38O mm. N 2 was used. In sucb a system the colour of the chlorophyll 

 remained unchanged. 



4. The yellow-green derivative, produced by the action of carbon dioxide 

 on chlorophyll, was precipitated by magnesium chloride and extracted with 

 ether. The ethereal extract was evaporated to dryness and the pigment 

 dissolved in alcohol. On addition of a trace of copper acetate to the boiling 

 alcohol solution a bright green colour appears. This reaction is character- 

 istic of the magnesium-free derivatives of chlorophyll. When the magnesium 

 of the chlorophyll molecule is replaced by hydrogen in the formation of 

 phseophytin this is accompanied by the colour change from green to yellow 

 or brownish- green already noted. On treating phseophytin with copper 

 acetate the hydrogen is replaced by copper, and with the re-entrance of a 

 metal (copper) into the chromogen complex, the colour changes back to a 

 brilliant green. This colour change is very striking. A similar green 

 compound is obtained when zinc acetate is used. 



The compound obtained with boric acid behaves in a similar way towards, 

 copper acetate. 



5. The yellow-green substance in ethereal and alcoholic solution was- 

 submitted to a careful spectroscopic examination. 

 It gave the characteristic absorption spectrum of 

 phseophytin, chiefly characterised by a strong 

 absorption band before the line E and another one 

 between the lines E and F. 



The substance obtained with boric acid gave an 

 identical spectrum. 



The experiments described under 4 and 5 were 

 also carried out with a true solution of chlorophyll in 

 alcohol (about 98 per cent.) which was subjected to 

 the action of carbon dioxide ; identical results were 

 obtained. A much greater amount of carbon dioxide 

 is necessary here, owing probably to the lesser 

 degree of ionisation of the carbonic acid in alcohol. 



Formaldehyde Test. — Tests for formaldehyde were 

 made after short and long exposures of the colloidal 

 solution in the presence of carbon dioxide and also 

 with the bicarbonate system. Various sources of illumination were used,, 

 sunlight, arc-lamp, mercury-vapour lamp, but in no case was any indication 

 obtained of the presence of formaldehyde. 



We have attempted, by means of the apparatus figured (fig. 1), to- 



