Mr Saunders, Photosynthesis and Hydrogen Ion Concentration 315 



A Note on Photosynthesis and Hydrogen Ion Concentration. By 

 J. T. Saunders, M.A., Christ's College. 



[Read 10 November 1919.] 



Last April (1919) I was testing the hydrogen ion concentration 

 of the water of Upton Broad, a small broad in Norfolk. I had 

 determined the hydrogen ion concentration of the water of the 

 broad itself to be 8-3 and I found this varied very Httle whether 

 the water was taken from the surface or the bottom, from near the 

 edge or the centre of the broad. The determination of the hydrogen 

 ion concentration was made by the use of standard solutions and 

 indicators as recommended by Clark and Lubs. 



When however the water in the shallow lodes and ditches 

 surrounding the broad was tested, great variations in the hydrogen 

 ion concentration occurred. The water became more acid as soon 

 as the broad was left and the ditches entered. At one end of the 

 broad where the water was shallow, not more than 18 inches deep, 

 and when there was no wind to mix it with the open waters of the 

 broad which was 6 feet deep, the hydrogen ion concentration 

 would fall to 8' 15. In the lode itself the hydrogen ion concentration 

 was 7-65. After boiling and rapidly cooling, water from the middle 

 of the broad and from the shallows both showed a hydrogen ion 

 concentration of 8'4, while that from the lode after the same treat- 

 ment was 8"15. 



At one point in the lode, however, I found surprising varia- 

 tions. Dippings of water from the same place gave readings of the 

 hydrogen ion concentration varying from 7-7 to 8-6. At this point 

 there was a certain amount of Spirogyra growing and I found that 

 if I took water from the centre of a mass of Spirogyra I could get 

 a reading as high as 9-0. 



I took some of the Spirogyra back with me and placed it in 

 test-tubes in tap-water which I coloured with indicator solutions. 

 The hydrogen ion concentration was 7-2 at the commencement of 

 the experiment. After standing the test-tube in a window in sun- 

 light the hydrogen ion concentration rose after an hour to 8-6 and 

 in two hours the phenolphthalein indicator had turned bright 

 pink, indicating a hydrogen ion concentration of more than 9-0. 

 I had no standard solutions with me which I could use to test 

 higher values than 9-0 so that I was unable to determine accurately 

 the ultimate result. I left the test-tubes until the next morning, 

 when I found the hydrogen ion concentration had fallen to 7-6. 

 After again placing the test-tubes in sunlight the hydrogen ion 

 concentration rose above 9-0. 



On my return to Cambridge I repeated these rough experi- 

 ments. It is easy to prove that the rise in alkalinity is not due to 

 alkali dissolved out of the glass, nor is it due alone to the abstrac- 



