302 Ayi'icujtural Chemistry. 



stituents of these minerals acquire a deg^ree of solubility in sol- 

 vents, which, while in the form of natural silicates, they either do 

 not possess, or possess in a far lower degree. While the silicates 

 are thus acted on, their silica or silicic acid (which is indispen- 

 sably necessary to the gramineae) is brought into a state in which 

 it is soluble in water, so that all the rain-water which comes in 

 contact with it finds and dissolves a certain quantity of silicic 

 acid beyond that quantity which the same amount of rain-water 

 would have found available without the ammoniacal salts.* By 

 means of the atmospheric constituents accumulated in the soil, 

 by means, for example, of ammonia, the action of the mineral 

 constituents which are present in available or soluble forms is 

 accelerated, that is, increased in a given time. 



By means of ammoniacal salts a part of the insoluble mineral 

 constituents present in the soil is rendered soluble, and a larger 

 fraction of the entire sum of mineral constituents is rendered 

 active, or capable of entering into the plant ; consequently, by 

 manuring with ammoniacal salts, there is removed from the soil, 

 in the excess of produce reaped in the first year, a part of those 

 mineral constituents which would have been rendered soluble and 

 available by natural causes in the second year. The soil, in the 

 second year, is i^oorer in these available mineral constituents than 

 it would have been had no ammoniacal salts been applied in the 

 preceding year. 



Of two fields, of which one has been manured with ammoni- 

 acal salts, and the other left unmanured, the former will give in 

 the first year a larger produce ; but if the same two fields be left 

 unmanured the second year, the proportions of produce will be 

 reversed. The field not manured in the first year must yield in 

 the second a decidedly higher produce than the other, because 

 the higher produce of the manured field in the first year must 

 have caused a greater consumption of mineral constituents, and 

 this must have produced a corresponding exhaustion of these con- 

 stituents ; consequently, a copious supply of ammoniacal salts 

 alone (if the mineral constituents removed in the excess of pro- 

 duce caused by this manure in the first year are not replaced) 

 cannot naturally exert any influence in the augmentation of the 

 produce of a field in the succeeding years, because the action of 

 these salts is in -part a chemical one. 



* Hydrated silicic acid is more soluble in pure watei' than in water containing 

 ammoniacal salts ; since, accoi-ding to the experiments of Way, and my own, am- 

 moniacal salts are removed from water by the soil, and lose their solubility, they 

 do not present any obstacle to the absorption of silica by the roots ; and lastly, 

 since on 1 acre of laud more than a million of pounds of rain-water falls, the 

 proportion of ammoniacal salts which can remain dissolved, where an excess of 

 them has been applied, is too trifling to form any material obstacle to the absorption, 

 of silica. 



