Agricultural Chemistry. 301 



actually evaporates through the leaves of plants, or that sulphate 

 of ammonia, or sal-ammoniac, can evaporate at all under these 

 circumstances. 



The most direct proof against this assumption (which in scien- 

 tific language is called a mere hypothesis, since it is destitute of 

 all foundation in fact) is the circumstance, that, when guano was 

 applied in Kuhlmann's experiments, not only was no loss of 

 nitrogen sustained, but in the hay obtained there was contained 

 64 per cent, of nitrogen beyond what was added to the soil in 

 the guano. This excess of 64 per cent, of nitrogen in the crop 

 was spread over the three years of the experiment as follows : — 



For 100 parts of nitrogen in the guano there was obtained in 

 the hay, — 



In 1844 lOSs parts of nitrogen. 



1845 22i 



1846 36 



Total nitrogen in the crops, including 100 



parts from the guano 164 parts. 



Consequently, in this experiment, not only no evaporation of 

 active or available nitrogen took place, but precisely the reverse 

 of loss occurred ; for an absorption and assimilation of nitrogen 

 from the natural sources, in addition to that in the guano, was 

 observed. 



The opinion or hypothesis that the nitrogen added to the soil 

 in excess, in manuring with nitrogenised manure, for example, 

 with ammoniacal salts, is taken up by the plants, loses its nutri- 

 tive power, and evaporates througli the stem and leaves, and that 

 the soil, by the cultivation of the gramineae, suffers a loss of 

 nitrogen, is shown by the preceding considerations to have no 

 scientific foundation whatever. The fact is, that when a field 

 has been manured with ammoniacal salts in one year, and has 

 jdelded in that year an increased produce, it yields, in the next 

 year, if sown with the same plant, a less abundant cro]) than an 

 equal surface of the same land in the second year, which has re- 

 ceived no ammoniacal salts in the preceding one. This de- 

 ficiency is a result of experiment ; but the conclusion drawn from 

 it, that it is caused by a loss of nitrogen, is not a true or logical 

 conclusion, but a mere fancy, an hypothesis. The deficiency is 

 explained by the following considerations. 



The effect of ammoniacal salts is not the same as that of free 

 ammonia. These salts contain an acid which exerts an action on 

 the constituents of the soil, an action not exerted by pure am- 

 monia. The acids of tlic ainuioniacal salts render the earthy phos- 

 phates more soluble in water tlian they would otherwise be. 

 These acids also render available the silicates : that is, they pro- 

 duce such a decomposition of the natural silicates, that the con- 



