392 



Mr. H. Wager. 



of distilled water are placed in the flask. A strip of potassium iodide paper 

 about two inches long is then attached to a cork, and the flask is corked up 

 so as to allow the strip of paper to hang down in the neck of the flask. 

 Another flask should be fitted up in precisely the same way but without 

 chlorophyll. Both flasks should now be exposed to the sunlight. The 

 bleaching of the chlorophyll takes place very rapidly. The strip of 

 potassium iodide starch paper becomes purplish blue in the chlorophyll 

 flask, showing that iodine has been liberated, but remains quite unchanged 

 in the control flask. The strip of potassium iodide starch paper is now 

 removed and a few more drops of distilled water are placed in the flask, 

 which is then corked and the contents well shaken up. The water in the 

 flask is then poured into two tubes. To one of these a few drops of Schiff 's 

 solution is added and a pink coloration soon develops, showing the presence 

 of an aldehyde. To the second tube a few drops of a 10-per-cent. solution of 

 potassium iodide is added, and then on the addition of a freshly made starch 

 solution, a blue or reddish-blue coloration is obtained, indicating the presence 

 of an oxidising agent capable of setting free the iodine in the potassium 

 iodide. 



If the bleaching has been continued long enough, the sides of the flask are 

 now covered with a thin white layer of a substance which should be well 

 washed to get rid of the remnants of the soluble aldehyde, and it will then 

 be found that this white substance is insoluble in either hot or cold water. 

 If, however, the bleaching is prolonged for a considerable time a much smaller 

 amount of the insoluble white substance remains. 



If we expose the chlorophyll paper behind coloured filters, we find that 

 both the aldehyde reaction and the potassium iodide reaction are much 

 stronger in the red than in the blue and weakest in the green. If, however, 

 the exposure behind the green and blue filters is prolonged to about 8 or 

 10 times that of the red, the reaction in the blue becomes as strong as in 

 the red. 



The reaction for aldehyde is therefore proportional to the bleaching effect, 

 and is approximately proportional therefore to the synthetic activity in the 

 different parts of the spectrum. 



The longer the light is allowed to act, the more completely does the 

 chlorophyll become bleached, with a corresponding increase in the aldehyde 

 reaction. In the case of the potassium iodide reaction, however, the converse 

 is the case. When chlorophyll films, either on paper or on glass, are sub- 

 mitted to the prolonged action of light, the reaction with potassium iodide is 

 much weakened, and may be completely absent. The explanation of this is 

 probably that the oxidising substance is a volatile gaseous product, which 



