300 Agricultural Chemistry. 



When the ammoniacal salts used as manure are accompanied by 

 mineral substances Avhicb are also elements of nutrition for plants, 

 the produce is proportional, not to the nitrogen in the manure, but 

 to the effect of these mineral substances. 



By the use of the phosphate of lime, the effect of the ammonia 

 in sal ammoniac was almost doubled. By the action of the sub- 

 stances which in guano accompany the ammonia, the effect of the 

 latter was made seven times greater than that of the same quantity 

 in the shape of sal ammoniac alone. By the addition of common 

 salt to the sulphate of ammonia, the effect of the ammonia in that 

 salt was increased 25 per cent. 



Since the effect of a manure is not proportional to the quantity 

 of nitrogen it contains, it will be easily understood why the value 

 of a manure cannot be estimated by its percentage of nitrogen. 



According to the best analyses, it may be assumed that meadow 

 hay contains 1 per cent, of nitrogen; consequently, in 100 parts 

 of nitrogen are contained 10,000 parts of hay. If we compare 

 with this quantity of hay the increased produce of hay produced 

 by 100 parts of nitrogen in Kuhlmann's experiments with ammo- 

 niacal salts, it appears that in this increase we only receive from 

 one-fifth to one-fourth of the quantity of nitrogen supplied in the 

 manure, and therefore that an apparent loss of four-fifths, or 

 three-fourths, of this nitrogen has taken place. 



In reality, no loss has occurred. That which might be re- 

 garded as loss is the portion of ammonia which has not acted ; 

 and this portion has not acted, because ammonia, by itself, pro- 

 duces no effect ; and only then does or can act, when the other 

 conditions are present which enable it to take a share in vege- 

 tation. 



It might be supposed that the portion of ammonia which has 

 not been assimilated, from want of the necessary conditions, has 

 yet been taken up by the roots, and has evaporated through the 

 stem and leaves, and that consequently no ammoniacal salt is left 

 in the soil after the harvest. Tliis idea is very unlikely to be 

 true, for it presupposes that the whole residue of ammonia, and 

 indeed every atom of it, has come into contact with the absorbent 

 root- fibres and been absorbed. This is impossible, for the ammo- 

 niacal salts are conveyed to every part of the soil ; but there are 

 not root-fibres in every part of the soil to absorb it, unless we 

 suppose the root-fibres to exert on the particles of ammonia scat- 

 tered in the soil the same influence which a pov/erful magnet 

 exerts on the particles of iroii filings, diffused through a heap of 

 sand. But we know that the root-fibres can only absorb those 

 particles which are in immediate contact with them, and that 

 they exert no attractive power even at the shortest distance. 

 Observation supplies no fact to prove, either that ammonia 



