298 LOSS OF MANURE. 



789. When animal substances are left for some 

 time exposed to the air, they undergo decomposition, 

 and there at last remains nothing but the more fixed 

 substances which they contained, together with a 

 quantity of salts of ammonia, formed during the de- 

 composition of the easily putrefiable matters. This 

 residue is a valuable manure, though in forming it a 

 very large portion of the ammonia produced is lost 

 by evaporation. The guano or huano of South 

 America, which has of late excited so much attention, 

 is the remains of the excrements of sea-fowl, which 

 has partly undergone this change (813). 



790. There are other modes besides that already 

 adverted to (162), whereby the loss of ammonia may 

 h& prevented. Both ammonia and its carbonate are 

 volatile, and though by the addition of water it is 

 easy to retard their escape, it cannot be entirely pre- 

 vented. It has therefore been proposed to add to 

 liquid manure a small quantity of some acid, which 

 shall combine with the ammonia to form a neutral 

 salt, and so prevent further loss from volatility. The 

 trials which have hitherto been made appear per- 

 fectly satisfactory, and the only question is — which 

 is the best method of thus neutralizing or fixing it ? 



791. The simplest method of fixing ammonia is to 

 add to the manure a small quantity of a weak solu- 

 tion of any acid; but we may also fix it by the addi- 

 tion of any salt containing an acid united to a base 

 by a less afiinity than the acid has for ammonia ; 



