158 IMPORTANCE AND VALUE 



required ; but in most cases a knowledge of its exter- 

 nal qualities will here be sufficient. In the excre- 

 ments and urine of those domestic animals which 

 produce the ordinary stall-manure, the farmer finds all 

 the elements united, that plants in cultivation re- 

 quire for their nourishment ; hence he rightly regards 

 them as a universal manure. It is otherwise with 

 artificial manures, whose constituents are extremely 

 various, and in which are seldom found all the sub- 

 stances necessary to the food of plants, but, as a gen- 

 eral rule, only a few individual ingredients. Hence 

 the farmer should not regard them as representatives 

 or substitutes for stable-muck, but rather as supplemen- 

 tary and accessory agents^ by which he is enabled to 

 heighten and increase the power of the latter. Every 

 practical agriculturist is aware that he cannot sup- 

 plant stall-manure by lime, gypsum, manuring salts, 

 ashes, brown-coal, and the like, but may probably 

 strengthen its action ; so, too, precisely, with most ar- 

 tificial manures ; and it must accordingly be of great 

 importance to the farmer, if he does not wish to make 

 experiments at random, and thereby sustain consider- 

 able loss, to know beforehand the principal constitu- 

 ents of the artificial manure he proposes to employ, 

 in order that he may be able to form a judgment 

 concerning its probable mode of operation. 



2. How rapidly does it act ? Upon this point the 

 chemical analysis of a manure can in many cases 

 furnish a conclusive reply. Those constituents 

 that are soluble in water, or become so by a prompt 



