446 Action of the Atmosphere iipon neivly-deepened Soil- 



The above calculations have, therefore, given the total amount 

 of nitrogen per acre brought down to the ground in a year in the 

 rain-water as under : — 



lbs. avoirdupois. 

 Average of Britain (low grounds) .. .. 11*258 



Alsace 9-092 



Paris 42-696 



It will be seen, therefore, how largely the soils in the neighbour- 

 hood of cities must be benefited by the manurial substances 

 brought down in the rain, if there is any confidence to be placed 

 in these figures.*" It must, however, be borne in mind that these 

 observations have been carried on but for very limited periods, 

 and also that the means at present existing for determining the 

 very minute quantities of these substances in the rain are not 

 very satisfactory ; indeed, with regard to the nitric acid, Mr. 

 Lawes, in a communication which he has favoured me with on 

 the subject, states that, in the opinion of the most eminent 

 chemists, it is doubtful whether there is any process known by 

 which the very small proportions of that ingredient can be accu- 

 rately determined. It may be interesting, however, to compare 

 these results with the quantities of nitrogen found in the crops 

 commonly grown in this country : a table, therefore, from Dr. 

 Anderson, of Glasgow, is subjoined, showing the amount of 

 nitrogen in pounds contained in average crops per impeiial acre 

 of the plants usually cultivated here : — 



Wheat . . 



Barley 



Oats 



Beaus 



Peas 



Turnip 



Potato 



Meadow-hay 



Red clover 



Flax 



Rye-grass 



In the Grain. In the Straw. 



38 



36 



60 



80 



75 



76 bulbs 



81 tubers 



44 



16 

 8 

 14 

 35 

 60 



50 tops 

 24 tops 



16 



Total. 



54 



44 



74 



115 



135 



126 



105 



57 



74 



60 



68 



It will be seen therefore that, according to the figures before 

 given, it is possible the rain in the precincts of a large city like 



* Since the above was written Mr. Way has published the results of an exami- 

 nation of the rain-water collected at Rothamsted in 1855, according to an improved 

 mode of analysis, by -which he found that the amount of nitric acid was very 

 much less than what Bari-al's results had led us to expect ; that indeed it con- 

 tributed far less nitrogen than the ammonia. The latter, however, he found in 

 greater quantity than Mr. Lawes had previously done, reaching to the amount of 

 7-11 lbs. per acre in the year, and in the proportion of r22S parts in a million of 

 water. 



