82 FERTILIZERS. 



those that fit special cases. . . . To compost fish-waste with 

 plaster and earth is more economical than to treat it with 

 acid." " The soil," says Professor Ville, " is the medium 

 in which we convert at pleasure phosphoric acid, potash, 

 and nitrogen into any crop we choose to grow." When 

 the animal matter in bones decays, the phosphoric acid in 

 the bones, say our scientific teachers, is in a reverted con- 

 dition. Says Professor Atwater, " The common impression 

 among farmers, that the best use of artificial fertilizers is 

 to supplement farm manures, is doubtless, in ordinary 

 circumstances, correct." Both Mr. Lawes and Professor 

 Ville are of the opinion that the largest crops are grown 

 by chemical manures. Salt-cake (sulphate of soda) con- 

 tains about forty per cent of sulphuric acid, and is an 

 excellent material to check decomposition. Under this 

 plea, it is used by some manufacturers with altogether too 

 liberal a hand in their fertilizers, for of itself it is of but 

 little value as plant-food. Nitre-cake, the refuse from 

 the manufacture of nitric acid, contains about forty-seven 

 per cent of sulphuric acid, and is an excellent material to 

 scatter over manure heaps, to hold the ammonia. The 

 difference between nitrogen in barnyard manure and in 

 ammoniacal salts (sulphate of ammonia, etc.) was strik- 

 ingly shown in some of the experiments of Mr. Lawes, 

 where forty-one pounds of nitrogen in the latter produced 

 as great effect on a crop of barley as did two hundred 

 pounds in the former. Dr. Voelcker found in perfectly 

 fresh horse-dung but one pound of free ammonia in fifteen 

 tons, though there was nitrogen enough to supply one 

 hundred and forty pounds of it. This suggests the wis- 

 dom of first composting, and so decomposing and making 

 it soluble, when we want prompt effects. Barnyard ma- 

 nures decompose faster in porous (sandy or gravelly) soils 

 than in compact ones. Says Professor Goessmann, " Good 



