276 



AMMONIA AND NITRIC ACID. 



risk of error, that the plants which grow in the culti- 

 vated fields of Europe have as much ammonia and nitric 

 acid furnished to them by the air and the dew, as is con- 

 veyed to them in rain-water. A sandy plain, where no 

 plants grow, receives from the rain as much ammonia 

 and nitric acid as a cultivated field ; but the latter de- 

 rives a greater quantity through the plants, and more 

 from the leafy plants, than from those which are poor 

 in leaves. Let us assume that in the Saxon experi- 

 ments the cereal plants, potatoes, and clover, raised 

 upon the unmanured land, derived the whole of their 

 nitrogen from the ground, and that nitrogenous food 

 had not been received either from the air or from the 

 dew ; then the profit and loss of the field in nitroge- 

 nous nutriment (according to the assumptions made p. 

 220, that T V of the nitrogenous constituents in clover 

 and potatoes were carried off in the form of cattle), 

 may be thus represented : 



The field at Cunnersdorf. 



At the beginning of the fifth year the field was therefore richer, 



in nitrogen, by 40'6 



