VI. MANUEING AND GENEKAL MANUEES 121 



An analysis of Damaraland guano l gave the following numbers : 



Moisture . . 19-00 per cent. 



Organic and volatile matters .... 33-94 



Including 



Total nitrogen . 7-72 



Ammoniacal nitrogen 

 Organic nitrogen 



Ash 



Nitric nitrogen 



3-26 

 4-00 

 0-46 



47-06 per cent. 



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 per cent, while the phosphorus pentoxide may reach 

 as high as 34 per cent and is usually above 23 per cent. 



The nitrogenous guanos are particularly valuable from the fact 

 that a large portion of their phosphates is soluble and the nitrogen 

 which they contain is in a readily available form, being present as 

 ammonium salts or in such easily decomposable substances as uric 

 acid, C 5 H 4 N 4 O 3 , or guanine, C 5 H 5 N 5 O, a body first obtained from 

 guano. 



Uric acid and guanine are interesting from their close relationships 

 to xanthine, C.H 4 N 4 O 2 , found in meat extracts ; to theobromine, 

 C 7 H 8 N 4 O 2 (dimethyl xanthine), the characteristic ingredient in cocoa ; 

 and to caffeine or theine, C 8 H 10 N 4 O 2 (trimethyl xanthine), the main 

 valuable constituent of coffee and tea (vide Chap X). 



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 indicated 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. 



Wagner 2 gives the table on the following page as the composition 

 of three samples of Peruvian guano. 



Pigeon and fowl dung. These substances, according to Storer, 3 

 were formerly much prized as manures, and played an important part 

 in Eoman, Persian and Egyptian husbandry. In France, too, large 

 dovecotes formerly constituted an almost necessary adjunct to farm- 

 steads. Their importance has diminished since the introduction of 

 nitrate of soda, kainite and other artificial manures. 



1 Earth, Jahr. iiber Agric. Chem., 1900, 118. 



3 Chemical Technology, 1892, p. 424. 3 Agriculture, Vol. I, 368. 



