i 



35 



by year niid month by month in the same way as the ammoniacal 

 nitrog-en and the rainfall until 1910, since when there has been no 

 simple relationship. 



Reasons are adduced for supposing- that the ammonia arises 

 from several sources. The sea, the soil and city pollution may all 

 contribute. Neither the sea nor city pollution seems able to 

 account for all the phenomena : the soil is indicated as an important 

 source by the fact that the ammonia content is high during periods 

 of high biochemical activity in the soil, .md low during periods cf 

 lo\\ biochemical activity. 



The close relationship between the .imounts of ammoniacal 

 and nitric nitrogen suggests either a comtnon origin or the produc- 

 ti<^n of nitric compounds from ammonia. 



'I'he average amoutU of chlorine is 2.4.S parts per million, 

 bringing down IBlbs. j)er acre per annum. The fluctuations 

 elosely follov. the rainfall both month by month and year by year, 

 but the gen(;ral level is mucli higlier during the months September 

 to April than during the summer months. It seems probable that 

 the chlorine comes from the sea, but some may come from fuel. 



vSince 1888, when the exj^eriments began, to 1916, when they 

 terminated, there has been a rise in the amounts of nitric nitrogen 

 and of chlorine in the rain. In the case of chlorine a parallel 

 series of determinations made at Cirencester over the same period 

 shows a similar rise. There is no rise of ammonia, but on the 

 contrary a tendency to drop : the sum of ammoniacal and nitric 

 nitrogen shows little change over the period. This seems to 

 suggest that a former source of ammonia is now turning out nitric 

 acid : it is possible that modern gas burners and grates tend to the 

 formation of nitric oxides rather than of ammonia. 



Rain contains on an average 10 parts of dissolved oxygen per 

 million, the amount being higher in winter than in summer: 

 66.41bs. per acre per annum were brought down during the two 

 years over which the determinations extended. 



The marked difference in composition between summer and 

 winter rainfall suggests that these may differ in their origin. The 

 winter rain resembles Atlantic rain in its high chlorine and low- 

 ammonia and nitrate content : the summer rain is characterised by 

 low chlorine but Wgh ammonia and nitrate content, suggesting 

 that it arises by evaporation of water from the soil and condensa- 

 tioti at higher altitudes than in the case of winter rain. 



CHANGES OCCURRING IN THE SOIL. 

 IX. E. J. Russell and E. H. Richards. '' The Washing 

 Out of Nitrates by Drainage IVater from Uncropped 

 and Unmanured Land." (Based on analyses made by 

 the late N. H. f. Miller.) Journal of Agricultural 

 Science, 1920. Vol. X. pp. 22-43. 



An investigation of the results obtained by the drain gauges 

 set up by Lawes and Gilbert in 1870. 



At the beginning of the experiment the soil contained 0.146% 

 of nitrogen, or about 3,5001b. per acre in the top 9 inches; it 

 yielded up to about 401b. of nitrogen per acre per annum to the 

 drainage water. At the end of nearly 50 years it still contains 

 0.099% of nitrogen, or 2,3801b. in the top'9 inches, and it still 



