130 NATURAL MANURES. VI. 



Moisture ... .. ... 19-00% 



Organic and volatile matters ... 33-94% 



Including Total nitrogen ... ... 7'72% 



Ammoniacal nitrogen ... 3-26 



Organic nitrogen ... 4*00 



Nitric nitrogen ... 0*46 



Ash ..- ... ... ... 47-06% 



Including Total phosphorus pentoxide 11-22% 



Soluble ,, ,, 3-87 



Potash ... ... 2-44 



Sulphur trioxide ... 5-06 



100-00 



In some samples the phosphorus pentoxide and potash are 

 higher in quantity. 



As types of the less valuable products, Baker Island, 

 Mexillones, and Lacepede guanos may be quoted. In these 

 the nitrogen varies from 0'5 to 2'0%, while the phosphorus 

 pentoxide may reach as high as 34% and is usually above 

 23 %. 



The nitrogenous guanos are particularly valuable from the 

 fact that a large portion of their phosphates are soluble and 

 the nitrogen which they contain is in a readily available form, 

 being present as ammonium salts or in such easily decom- 

 posable substances as uric acid, C 5 H 4 N 4 O S , or yuanine, C 5 H 5 N 5 0, 

 a body first obtained from guano. 



Uric acid and guanine are interesting from their close rela- 

 tionships to xanthine, C 5 H 4 N 4 0. 2 , found in meat extracts ; to 

 theobromine, C 7 H 8 N 4 0. 2 (dimethyl xanthine), the characteristic 

 ingredient in cocoa; and to caffeine or theine, C K H 10 N 4 O 2 

 (trimethyl xanthine), the main valuable constituent of coffee 

 and tea (v. Chap. XI.). 



In the phosphatic guanos the phosphoric acid is mainly 

 present as tricalcium phosphate, and therefore not easily 

 available to plants. Such guanos are often used for conversion 

 into superphosphate. 



The chemical nature of guano is highly complex, as is indi- 

 cated by what has already been said. It is almost impossible 

 to say how the various acids and bases present in such a 

 mixture are distributed, but attempts to do so have been made. 



