E. J. Russell and E. H. Richards 315 



Anderson^ has argued that the values for nitric nitrogen are a function 

 of the weather type which they may therefore help to characterise. 



At Rothamsted the rain falling during the months May, June, 

 July, August and October is richer in nitrate than that falling in 

 January, February, March and April. This is similar to the distribution 

 of ammonia. Examination of the curves of Fig. 1 shows that the nitric 

 nitrogen fluctuated with the rainfall in nuich the same way as the 

 animoniacal nitrogen until 1910, but since then there has been no simple 

 relationship. The monthly fluctuations shown in Fig. 2, also follow the 

 rainfall and the ammonia. 



For most of the period the relationship between ammoniacal and 

 nitric nitrogen has been close and was almost exactly 2:1. Since 

 1912, however, the nitric nitrogen has increased so that on the four 

 year average the nitric nitrogen is equal to the ammoniacal nitrogen, 

 instead of being only half as much. This is not the result of a general 

 rise throughout the whole of the year, but of a few exceptionally high 

 values in the months February, March, July, August and October. 

 During this period it happened that the rainfall in February and March 

 has been unusually high; there was also one very wet July. 



Ammoniacal and nitric nitrogen in rain: four year periods. 



Four years' Deriod f^^P*- 1^^^- ^^^'^- ^^^'^- ^^^^- ^^^^ ^^^^ ^^^^ 

 rour years perioQJQ^j^ jgg, iggg 1900 1904 1908 1912 1916 



Nitric nitrogen ... 0-98 1-08 l-2(i 1-43 1-28 1-48 1-75 



Ammoniacal nitrogen 2-82 2-63 2-68 2-98 2-54 2-97 1-84 



Sum ... 3-80 3-71 3-94 4-41 3-82 4-45 3-59 



imonia( 

 Nitric 



Ratio: ^^nE~l nitrogen 3:1 5:2 2:1 2:1 2:1 2:1 1:1 



The increase is jiresumably due to some artificial cause, though it 

 is not easy to say what. During the period 1886 to 1908, which saw 

 an enormous expansion of London into the Home Counties and a pushing 

 out both of industrial concerns and of private residences, there was only 

 a small rise in nitrate and none in ammonia. It is possible that the 

 changes in stoves and gas-burners, which had become marked by 1912, 

 and which have reduced the frequency of London fogs, have also tended 

 to increase the nitrous fumes rather than the ammonia in the atmosphere. 



The rain coming from the Atlantic contains much less nitrate than 

 that falling in inland stations (see p. 317). 



1 V. G. Ancler.son, Joiirii. Roij. Melenml. Hoc, 191."), 41, 99. 



