296 A3IM0NIA AND NITRIC ACID. 



nitrogenous substances, which could not be made effective 

 until their nitrogen had been converted into ammonia. 



The effect of guano in raising large crops of com was 

 undeniable ; hence it was according to theory assumed 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 followed, therefore, 

 as a matter of course, that the operation of guano could 

 be produced by substituting a corresponding quantity of 

 salts of ammonia ; and the partisans of this theory 

 beheved that to increase corn crops at pleasure, nothing 

 further was necessary than to procure the requisite quan- 

 tity of salts of ammonia at a reasonable price. Humus is 

 the only thing wanting ; such was the earher opinion. 

 Now, it is ammonia is the only thing wanting. 



This conclusion was an immense step in advance as 

 regards the views of the importance of nitrogen for 

 plants. Instead of attaching no determinate idea to the 

 word ' nitrogen,' the term had now a fixed and definite 

 meaning. That which formerly was called nitrogen was 

 now termed ' ammonia,' an intelhgible, ponderable com- 

 pound separable from all other substances which are 

 likewise constituents of nitrogenous manures, and capa- 

 ble of being used in experiments, in order to test the 

 truth of the theory itself. 



If the operation of guano bore any proportion to its 

 nitrogen, then a quantity of ammonia containing an equal 

 amount of nitrogen must produce not only the same, but 

 a much greater effect; for one-half of the nitrogen in 

 guano exists in the form which is difficult of assimilation, 

 whereas the ammonia could be entirely assimilated. 



If in any single experiment, the guano produced a 

 powerful effect, and the corresponding quantity of am- 



