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Mr Saunders, The Ammonia Content of the Waters, etc. 471 
The Ammonia Content of the Waters of Small Ponds. By 
J. T. Saunpers, M.A., Christ’s College. 
[Read 4 May 1914.] 
Notre. The ammonia referred to in this paper is the “free” 
ammonia and the amount is expressed in grammes of NH, per 
million cubic centimetres of water. 
Free ammonia is always present in the waters of small ponds, 
but the amount varies very greatly. In ponds where there is 
sewage contamination such as horseponds, the amount is very 
high, as much as 16:2. Here the variation is chiefly affected by 
the amount of sewage that is introduced. Where there is no 
sewage contamination the amount is much lower, the maximum 
quantity for such a pond is about ‘500—‘600. 
Broadly speaking it is in the winter that the greatest quantities 
of ammonia are found in uncontaminated ponds, and the amount 
falls off during the spring to rise again in the autumn to its winter 
maximum. This is the annual cycle of changes. Changes how- 
ever take place from day to day, and even different layers of 
water show slightly different quantities of ammonia. 
One of the chief factors controlling the ammonia content in 
these small ponds is the amount of the rainfall. Copious rain 
after a period of sunshine effects a very considerable reduction in 
the ammonia present, a reduction that is out of all proportion to 
the extra amount of water that has entered the pond. 
During the present year February was a dry month; there 
was only a total of ‘85 inch* of rain on 13 days. But “March 
was extremely wet, the wettest but one on record for 50 years. 
On 24 February the ammonia content of a small pond on Sheeps’ 
Green, Cambridge, was -425. It continued to remain at about 
this evel until the beginning of March. On 4 March the amount 
contained was ‘400, but on 10 March the amount had fallen to 
‘213. This fall I attribute to the heavy rains, for on the two 
previous days 58 inch of rain had fallen and ‘there had been 
‘75 inches since 1 March. The ammonia content continued at 
-a low level during the wet weather of March. On 17 March 
the ammonia content had sunk to ‘115, and on 18 March it was 
further lowered to 060. This second fall again may be attributed 
to heavy rain, for on 16 March °25 inch of rain had fallen and 
* The rainfall was measured by Mr Pain of Sidney Street, Cambridge, who very 
kindly allowed me to use his records. 
31—2 
