STRONG MANURES.

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hair, wool, skin, and lastly horns, hoofs, and bones.These substances are all more or less valuable, asyielding to the soil a large quantity of the substanceswhich constitute the food of plants; they putrefy,and their elements form new combinations with greatrapidity. Those which change most readily of courseyield ammonia and carbonic acid most rapidly, andthese constitute the most powerful manures: thosewhich decompose more slowly are less powerful, butmore lasting in their effects.

418. Urine, dung, and the decaying carcases ofanimals are for manypurposes considered to be too strong,and means are adopted to diminish their power. Thesemanures evolve during their rapid decay, a very largequantity of ammonia, carbonic acid, &c. far more in factthan plants require or can absorb. The excess is hurtfuland must be prevented.

419. There are two ways by which this may beeffected, the one is to mix strong manure with a con-siderable quantity of some substance far less prone todecomposition, so as to dilute it, or check its decay; theother, and certainly infinitely the worst way, is toexpose it to the air for some time, and not to use it untila great part of the ammonia evolved by its decay is dissi-pated,—what remains is then sufficiently mild to be usedwith safety.

420. In order to save as much as possible the valuableparts of these manures, they should be mixed with acertain quantity of vegetable refuse matters, such as