350 Mr Saunders, Hydrogen Ion Concentration of Natural Waters 



A Note on the Hydrogen Ion Concentration of some Natural 

 Waters. By J. T. Saundees, M.A., Christ's College. 



[Read 7 March 1921.] 



The natural waters referred to in this preliminary note are all 

 fresh and all occur in districts where the soil or sub-soil contains 

 chalk, gault or hme in some form or other. In such districts the 

 natural waters have a fairly constant hydrogen ion concentration. 

 When the water issues from the ground as in the case of springs 

 and wells the Ph is found to vary only within the hmits 7- 1-7-2. 

 The following table shows the values of Ph for water issuing from i 



the ground: « 



Locality 



Well at Cherryhinton, Cambs 



Springs at Shelf ord ("Nine Wells"), Cambs.... 

 Siphon spring at Warlingham, Surrey 

 Cambridge tap water (supplied from wells)... 



These four cases are all very different yet the Ph of the water is 

 remarkably constant. The well at Cherryhinton is 8 ft. deep with 

 2 ft. of water at the bottom. The water comes through the gault. 

 At Shelf ord the "Nine Wells" are a number of springs bubbhng 

 up through fissures in the chalk. The siphon spring at Warhngham 

 is intermittent, running freely for eight to ten weeks at intervals 

 varying from two to seven years. Here, as at Shelford, the water 

 comes up through fissures in the chalk. The Cambridge Town 

 supply is derived from deep wells running through the gault to 

 water-bearing strata. 



As the water leaves the source and flows along in the stream 

 that arises from the spring the value of Ph increases gradually 

 until it reaches a value varying only within the Hmits 8-25-8'5, 

 at which value it remains constant. The siphon spring water at 

 Warhngham flowed along a wide grassy ditch. Within half-a-mile 

 of the source the Ph of the water had risen to 8-4 at which value 

 it remained constant for, at any rate, another mile, when I was 

 unable to trace it further. The water flowing from the "Nine 

 Wells" at Shelford behaves in much the same fashion, but here 

 I was able to trace the water further and found that the Ph, after 

 reaching the value 8-3 %\ithin half-a-mile of the source, fell again 

 at a mile and a half from the source to 8-05. This lowering of the 

 Ph is undoubtedly due to the stream, which has now become 

 almost sluggish, mixing with its waters the acid products of de- 

 composition from the bottom. At first the stream flows over clean 



