EXPERIMENTS WITH SALTS OF AMMONIA. 281 



cure the requisite quantity of salts of ammonia at a 

 reasonable price. Humus is the only thing wanting ; 

 such was the earlier 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 intelligible, 

 ponderable compound separable from all other sub- 

 stances which are likewise constituents of nitrogenous 

 manures, and capable 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- 

 monia was inoperative or weaker, this experiment 

 would be amply sufficient to confute the notion which 

 had been attached to nitrogen. For if this notion was 

 correct, the ammonia ought to operate in all cases in 

 which the guano operated, and exactly in the same 

 manner. The oldest experiments in this direction were 

 made by Schattenmann (* Compt. rend.' t. xvii.). 



He manured ten plots of a large wheat-field with 

 sal ammoniac and sulphate of ammonia ; an equally 

 large plot remained unmanured. Of the manured 

 plots, one received 162 kilogrammes ( 356 Ibs. Eng.) 

 per acre ; the others received the double, treble, and 

 quadruple quantity of each of these salts. 



The salts of ammonia (says Schattenmann, p. 1130) 

 appear to exert a remarkable influence upon wheat ; 

 for, only eight days after manuring, the plant assumed 

 a deep dark-green colour, the sure sign of high vegeta- 

 tive power. 



