GENEEAL MANTJEES ANIMAL AND VEGETABLE 295 



is therefore immediately available, and the remainder 

 readily becomes so. Such conditions are associated with 

 the highest degree of fertilising power of any given 

 quantity of plant food, and they do not generally, 

 obtain in artificial guanos. 



Nitrogenous and Phosphatic Guanos. In moist climates 

 fermentation takes place much more rapidly, and a large 

 proportion of the nitrogen and other soluble constituents 

 is lost. In some cases they have been completely re- 

 moved and only the insoluble tricalcic phosphates remain. 

 These are the phosphatic guanos previously referred to. 

 They are chiefly employed for the manufacture of super- 

 phosphates. The latter are sometimes called dissolved 

 phosphatic guanos, but they have no greater manurial 

 value than the superphosphates prepared from mineral 

 apatites and phosphorites. Guanos which contain con- 

 siderable, or even appreciable quantities of nitrogen, are 

 by contrast, called nitrogenous guanos, but it is to these 

 and these only that the unqualified word guano usually 

 and properly refers. 



Sources and Quantities. Nitrogenous guanos were first 

 discovered in Peru, and the largest quantities are still 

 obtained from that country. Deposits were subsequently 

 found in various parts of South and North America, West 

 Indies, Australia, Pacific Islands, etc., but most of them 

 were of inferior quality and some were purely phosphatic. 

 Peruvian guanos were mostly of very high grade, and the 

 term has sometimes been regarded as synonymous with 

 nitrogenous guano. 



The quantity of guano consumed in this country has 

 varied considerably from time to time as new deposits 

 were discovered and became exhausted. In the year 1870 

 it amounted to nearly 250,000 tons, and in 1887 it was 

 only a little over 5,000 tons. 



The following table shows the quantity of guano im- 



