332 



Rain FaUinfj at Rothamsted 



Table 2. Nitrogen as ammonia and nitric acid in rainwater 

 collected at Rothamsted. 



The analjrtical determinations are carried out once a month on a sample made up from 

 the daily collections. After each wet day a sample is taken from the gauge proportional 

 in amount to the rainfall : one decigallon per inch of rain : this is kept in a Winchester 

 quart bottle. At the end of the month the whole sample is measured and should corre- 

 spond with the total rainfall. 



The average figures quoted in the tables are true averages of rainfall and Iba. per acre 

 but not of parts per million. In the latter case the figure shows the number of parts which 

 when multiplied by the average rainfall gives the average number of lbs. per acre. This 

 is the old Rothamsted convention and has been in use so long that change would be a 

 serious matter. The figures are usually not widely different from the true averages, but 

 no definite relationship exists between them. 



