236 PERUVIAN GUANO, ETC. [chap. 



mittently, when the requirements of Cape Colony 

 have been satisfied. 



Ichaboe guano only represents the deposit of a 

 single year, it is thus very fresh and distinguished by 

 the undecomposed feathers it contains. With about 8 

 per cent, of nitrogen, it is usually proportionally less 

 rich in phosphoric acid than a similar grade of Peruvian 

 guano would be. It usually also contains more sand. 



On the many other oceanic islands where guano has 

 been deposited, the occasional rains or heavy dews have 

 been sufficient to remove the soluble nitrogen com- 

 pounds and even in time the organic nitrogen bodies, 

 which in the presence of moisture have been able to 

 decay and break down into soluble material, leaving 

 behind a residue consisting mainly of phosphate of 

 lime. In other cases chemical reactions have taken 

 place with the calcium carbonate of the coral rock on 

 which the deposit happened to be formed, resulting in 

 the production of a calcium phosphate, containing some- 

 times rather a large proportion of iron and alumina. 

 These phosphates, at one time of importance in the 

 manufacture of superphosphates, will be dealt with 

 under phosphatic manures. 



Besides the true guanos derived from bird drop- 

 pings and the closely allied bat guanos, small deposits 

 of which are found in caves in America and South 

 Africa but which possess no commercial importance, a 

 good many other substances containing nitrogen and 

 phosphoric acid are called guano, though they have no 

 proper claim to the title. For example, the residues 

 from various processes dealing with fish {e.g., in the 

 preparation of cod liver oil, the curing of herrings, the 

 tinning of sardines, etc.), are dried and reduced to a 

 powder, which is sold as " fish guano " ; and again, meat 

 residues, such as accumulate in the manufacture of meat 



