398 



Mr. H. Wager. 



on the chlorophyll of laminaria brings about the production of an oxidising 

 substance capable of effecting the decomposition of iodine compounds which 

 may be contained in the chlorophyll cells of the plant, and that the iodine 

 thus set free may either escape or be re-absorbed by the slime which occurs 

 in such abundance in laminaria. 



The Photo-decomposition of Chlorophyll takes place only in the Presence of 



Oxygen. 



Three test-tubes were taken and lined with a film of chlorophyll by the 

 careful evaporation of a petroleum ether solution of grass chlorophyll. 

 One was placed with its open end in a strong solution of potassium hydrate 

 and pyrogallol, to absorb the oxygen ; the second was placed in a strong 

 solution of potassium hydrate to absorb the carbon dioxide, and the third 

 was placed in distilled water. All three were kept in the dark for 

 24 hours, and were then exposed to the light. The second and third 

 bleached very rapidly. The first, which contained no free oxygen, remained 

 unbleached even after an exposure of some months. At the time of 

 writing, it has been exposed for four months in a south window and is 

 still unbleached. The second and third gave strong reactions both for 

 aldehyde and for the oxidising agent. The experiment shows quite clearly 

 that the bleaching of chlorophyll is the result of oxidation brought about 

 under the influence of light. 



If this is correct, it occurred to me that we ought to be able to show that 

 oxygen is absorbed in the process. To test this, I obtained four tubes 

 16 cm. long and 4 mm. in diameter ; they were drawn out at one end 

 to a point, which was then broken off, so as to leave an opening less than 

 1 mm. in diameter. Three of these were lined with chlorophyll from a 

 petroleum ether solution. Care was taken to get rid of all traces of the 

 ether by forcing a stream of air through the tubes for some time. I found 

 a bicycle pump useful for the purpose. The fourth tube contained no 

 chlorophyll and was simply used as a control. The three chlorophyll tubes 

 and the empty tube (No. 4) were then placed with their open ends down- 

 wards in distilled water contained in two separate beakers. The water 

 was at a sufficient depth to allow of its entry into the tubes to a height 

 of 2 cm. This was done to allow of the expansion of the air in the tubes 

 when they were exposed to the heat of the sun. The upper narrow ends 

 of the tubes were then sealed with the bunsen flame. They were all 

 placed in the dark for 12 hours. The next day they were all carefully 

 measured, and it was found that the water was at the same height in 

 each tube. One of the chlorophyll tubes and the control tube were then 



