THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 443. 



annual yield of Nitrogen in our crops. The amount of Nitrogen derivable from these 

 sources is, moreover, perhaps more readily quantitatively estimated than that from any 

 of the other sources enumerated. Accordingly, much labour has, of late years, been 

 bestowed in determining the amounts of ammonia and nitric acid in these several aqueous 

 deposits. Extensive series of observations have been made on these points by Boussix- 

 gault, Bakral, Way, and two of ourselves; and others have experimented on a more 

 limited scale. It may be stated, generally, that the rain of the open country has indi- 

 cated an average of very nearly the same amounts of ammonia in the hands of Boussix- 

 gault in Alsace, and of Wat and ourselves in England. The most numerous and reliable 

 determinations of the amount of nitric acid in rain-water are probably those of Mr. Way. 



By the aid of numerous determinations of the ammonia by ourselves, and of both the 

 ammonia and nitric acid by Mr. Way, we are enabled to form an estimate of the total 

 amount of Nitrogen coming down as ammonia and nitric acid in the total rain, hail, 

 and snow, and in some of the minor aqueous deposits, during the years 1853, 1855, 

 and 185G, here at Rothamsted, where the experiments relating to the acreage yield of 

 Nitrogen in the different crops were made. The result was, that in neither of the three 

 years did the Nitrogen so coming down as ammonia and nitric acid amount to 10 lbs. 

 per acre. 



Supposing the combined Nitrogen coming down in the direct aqueous deposits were 

 to be estimated, in round numbers, at 10 lbs. per acre, per annum, this amount would 

 supply less than half as much Nitrogen as was annually removed in the continuously 

 grown wheat and barley crops. It would amount to only about one-fourth of that 

 which was obtained in the hay, and in the turnips ; to a less proportion of that obtained 

 in beans ; and to a still less proportion of that obtained in the clover. Lastly, it would 

 amount to only about one-fourth as much as was obtained per annum, over twelve years 

 of ordinary Rotation, but without manure of any kind either during that period or for 

 some year's previously. 



We are driven, then, to seek for other sources of the Nitrogen of our crops, than 

 that which comes down as ammonia and nitric acid in the more direct and more easily 

 measurable aqueous deposits from the atmosphere. Nor does it appear, so far as can 

 be judged from the results of Boussingault on this point, that the amounts of combined 

 Nitrogen deposited by dew are such as to lead to the supposition that our approximate 

 estimate would require any material modification, were as large a proportion of dew 

 included in our collected and analysed aqueous deposits as is probably received by the 

 soil itself or the vegetation which may cover it. 



(3) With regard to the amounts of combined Nitrogen accumulated by the soil from 

 the atmosphere by virtue of surface absorption, or chemical action, it is probable that 

 they constitute no inconsiderable proportion of that which is annually available for 

 vegetation over a given area of land. Numerous investigations have indeed been under- 

 taken during the last few years, both by ourselves and others, to determine the actual or 

 relative capacities for absorption of different soils, or constituents of soils. Unfortu- 



