Mr Saunders, Hydrogen Ion Concentration of Natural Waters 351 



ground, there is no debris and the bottom is swept clean by the 

 force of running water. But further on the stream expands, its 

 pace slackens and debris accumulates at the bottom. In rivers and 

 streams, however sluggish, there is sufficient stream to mix the 

 waters thoroughly and to bring up the acid waters from the bottom. 

 Hence the Ph of rivers and streams is variable and not constant, 

 depending on the pace of the stream and the amount of disturbance 

 of the bottom. 



In ponds and lakes that are large and deep, no disturbance of 

 the bottom will occur and there is no general mixing of the waters. 

 Here again we find the Ph to be constant mthin the hmits 8-25-8-5 

 as the following table shows: 



Locality 



Upton Broad, Norfolk 



S. Walsham Broad, Norfolk 



Railway Ballast Pits, Chesterton, Cambridge.. 



Large Brick Pit, Cambridge 



,, „ Madingley 



The two Broads in Norfolk are large shallow waters not more 

 than 6-8 ft. deep. The pits at Cambridge and Madingley are 

 20-30 ft. deep. The area in all cases exceeds an acre. In small 

 shallow ponds no such constancy occurs. Here the influence of 

 the bottom will cause a lowering of the Ph; the presence of masses 

 of vegetation, however, may increase the Ph, for plants, during 

 photosynthesis, extract COg from bicarbonates and render the 

 water alkaline. If, on a sunny day, water be taken from a small 

 pond containing masses of Spirogyra the value of the Ph will be 

 found to be as much as 9-0. 



On shaking in a test tube well or spring waters from these 

 districts where lime in some form or other is abundant in the soil 

 or sub-soil, it is found that Ph rises to a value varying from 8-25-8'5 

 and remains constant within these hmits. Bubbhng air through the 

 water produces the same effect. If the effects of decomposition and 

 photosynthesis be avoided it will be found that the Ph of waters 

 in these districts when saturated with air in solution has a value 

 that is constant within the hmits 8-25-8-5. 



The method used for the determination of the value of Ph has 

 been that developed by Clark and Lubs. 



REFERENCES. 



Clark and Lubs. "The Colorimetric Determination of Hydrogen Ion Con- 

 centration." J. Bad. 1917, II. 1, 109, 191. 



OsTERHOUT and Haas. "The Dynamic of Photosynthesis." J. Oen. Physiol. 

 1918, I. 1. 



23—2 



