284 AMMONIA AND NITKIO ACID. 



If the crops were equal, it would be manifest that the 

 insoluble constituents of the guano had no effect : if the 

 crop upon the plot manured with guano was greater, 

 it would be certain that the insoluble constituents 

 (mineral constituents, as Messrs. Lawes and Gilbert 

 would term them) had some share in producing the 

 additional crop. The extent of this share could per- 

 haps be determined, if a third plot were manured with 

 the insoluble constituents, i. e. with the lixiviated resi- 

 due of an equal quantity of guano. 



If an experimentalist, in carrying out his proof, in- 

 stead of following this method, had, on the contrary, 

 lixiviated the guano, and manured a plot of ground in 

 \hsfirst year with the insoluble constituents of the guano, 

 and in the subsequent years, with the soluble constitu- 

 ents and if he had maintained that these soluble con- 

 stituents, in other words, the salts of ammonia in the 

 guano, had alone produced the high additional crops, 

 and that these bore a' proportion rather to the salts of 

 ammonia than to the incombustible constituents in the 

 guano, we should have good grounds for concluding 

 that he had simply deceived himself ; for, in point of 

 fact, the field had been manured, not with salts of am- 

 monia alone, but with all the constituents of the guano. 



What has here been said in reference to guano, 

 which, as before mentioned, has the same effect as a 

 mixture of superphosphate, potash, and salts of am- 

 monia, may be literally applied to the experiments of 

 Lawes and Gilbert. 



They manured their field, in the first year, with a 

 quantity of soluble phosphoric acid, lime, and potash, 

 which very nearly corresponds with the amount of these 

 substances in 1750 Ibs of guano ; and in the subsequent 

 years they applied salts of ammonia. The arable sur- 

 face soil of the field had, by previous cultivation, been 

 manifestly exhausted of nitrogenous food ; and, under 

 these circumstances, the only wonder would have been 

 if the nutritive substances which operate in guano had 

 been able, without ammonia, to yield as large a crop as 

 wiih> ammonia. 



