300 AMMONIA AND NITKIC ACID. 



lixiviated the guano, and manured a plot of ground in tlie 

 first year with the insoluble constituents of the guano, and 

 in the subsequent years, with the soluble constituents — and 

 if he had maintained that these soluble constituents, 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 

 liimself ; for, in pomt of fact, the field had been manured, 

 not with salts of ammonia alone, but with all the consti- 

 tuents of the guano. 



What has here been said in reference to guano, 

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

 mixture of superphosphate, potash, and salts of ammonia, 

 may be hterally applied to the experiments of Lawes and 

 Gilbert. 



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

 tity of soluble phosphoric acid, hme, and potash, which 

 very nearly corresponds with the amount of these sub- 

 stances in 1750 lbs. of guano ; and in the subsequent 

 years they apphed salts of ammonia. The arable surface 

 soil of the field had, by previous cultivation, been mani- 

 festly 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 

 with ammonia. 



These experiments are worth notice in the history of 

 agriculture, because they show what statements could be 

 laid before farmers, at a time when ignorance of first 

 principles did not yet permit scientific criticism. 



With regard to the influence of ammonia and salts of 

 ammonia, there was instituted in the years 1857 and 



I 



