132

LOSS OP MANURE.

acid and ammonia; the latter, those very substanceswhich we require to add to the soil, those very substanceswhich are removed with crops. In consequence of thevolatile nature of the products of decay, every meansmust be employed to prevent their loss.

409. When animal substances are left for some timeexposed to the air, they undergo decomposition, and thereat last remains nothing but the more fixed substanceswhich they contained, together with a quantity of salts ofammonia, formed during the decomposition of the easilyputrefiable matters. This residue is a valuable manure,though in forming it a very large portion of the ammoniaproduced, is lost by evaporation. The guano of South America , which lias of late excited so much interest, is theremains of the excrements of sea-fowl, which has under-gone this change.

410. There are other modes besides that alreadyadverted to (403), whereby the loss of ammonia maybe prevented. Both ammonia and its carbonate arevolatile, and though by the addition of water it is easyto retard their escape, it cannot be entirely prevented.It has therefore been proposed to add to liquid manurea small quantity of some acid, which shall combine withthe ammonia to form a neutral salt, and so preventfurther loss from volatility. The trials which havehitherto been made appear perfectly satisfactory, and theonly question is—which is the best method of thus neu-tralisms or fixing it ?

411. The simplest method of fixing ammonia is to