280 AMMONIA AND NITRIC ACID. 



with regard to the rapidity of its action. The fact that 

 the influence of guano in increasing the crops was gen- 

 erally more rapid than that of other manures contain- 

 ing an equal amount of nitrogen, made it evident that 

 some one of its constituents possessed a peculiar power 

 which was not present in the other manures ; and this 

 constituent was supposed to be more conducive than 

 other nitrogenous compounds to the growth of plants. 



The discovery of this constituent presented no diffi- 

 culty. Chemical analysis showed that Peruvian guano 

 was very rich in salts of ammonia, and that one-half of 

 its nitrogen existed in the form of ammonia. But am- 

 monia was already well known as an element of nutri- 

 tion for plants, and this afforded an easy solution of the 

 rapidity which marked the operation of guano. Peru- 

 vian guano accordingly contained in a concentrated 

 state in the ammonia one of the most important nutri- 

 tive substances for plants, and this nutriment when 

 dispersed in the soil could be directly assimilated by 

 their roots. 



From this time forward a distinction was drawn 

 between the various kinds of nitrogenous manures, and 

 ' assimilable ' nitrogen was discriminated from that 

 which was termed ' sparingly assimilable.' Assimila- 

 ble nitrogen was understood to mean ammonia and 

 nitric acid ; but the term ' hard of assimilation ' was 

 applied to other nitrogenous substances, which could 

 not be made effective until their nitrogen had been con- 

 verted into ammonia. 



The effect of guano in raising large crops of corn 

 was undeniable ; hence it was according to theory as- 

 sumed as incontestable, that its operation depended 

 upon the amount of nitrogen contained in it ; it was 

 further considered as certain, that ammonia was the 

 most effective portion of the nitrogen in guano. It fol- 

 lowed, therefore, as a matter of course, that the opera- 

 tion of guano could be produced by substituting a cor- 

 responding quantity of salts of ammonia ; and the par- 

 tisans of this theory believed that to increase corn crops 

 at pleasure, nothing further was necessary than to pro- 



