Organic Manures 



flesh of the fish the proportion of phosphates 

 diminishes, and that of nitrogen increases. The 

 flesh of fish, like that of other animals, contains 

 about 15I per cent, nitrogen, and only a little 

 phosphoric acid, while the bones contain many 

 phosphates and a good quantity of nitrogenous 

 organic matter. Guano made by drying over an 

 open fire loses a part of its nitrogen during the 

 process. 



Generally in well-managed works the prepara- 

 tion is made in closed pans, and there is no loss. 

 In such places the oil is extracted more or less per- 

 fectly to be used in the manufacture of soap. 



Some makers dry the fish insufficiently, and 

 then the guano can contain as much as 35 per 

 cent, water. This water not only uselessly takes 

 the place of the manure, which is consequently im- 

 poverished, but when the guano is stored causes loss 

 of nitrogen in ammoniacal form by fermentation and 



fungi. 



Fish guano rarely contains any great quantity 

 of silicate matter, when present in any quantity it 

 denotes impurity. 



It is obvious, then, that fish guano varies con- 

 siderably in quality. Its purchase needs close 

 attention, and it must never be bought without 

 analysis, because its value can vary from single to 

 double or even more, and will do so especially 

 according to the proportion of nitrogen which is 

 found in it. The price of the units must be com- 

 pared with those of other commercial products, and 

 purchase only be made when the prices are found 

 to be favourable. 



112 



