68 BOARD OF AGRICULTURE. [Jan., 



these places are subject to more or less frequent rains which wash. 

 back into the ocean whatever is freely soluble in the bird deposits, 

 or else these soluble matters enter into chemical reaction with the 

 coral limestone and are in part retained. As a rule the nitrogen 

 and potash are lost while the phosphates are retained and become 

 a valuable source of phosphoric acid, forming what are called the 

 phosphatic guanos. 



In former years we received a great deal of this material from 

 some small Pacific islands of coral formation under the name of 

 American guano. In 1856 the United States assumed the pro- 

 tection of all the guano islands in the Pacific which lay within 10° 

 of the equator north and south, and between longitude 150° and 

 180°. The islands chiefly worked were Baker's, Rowland's, and 

 Jarvis'. 



The guano was brown, pulverulent and coarse grained, and 

 could be shoveled without picks. It contained from 30 to 40^ of 

 phosphoric acid, and that from Jarvis' Island was largely neutral 

 phosphate of lime instead of basic phosphate, a point in its favor 

 when used for the preparation of superphosphate, for it required 

 less oil of vitriol to dissolve it. 



But at present nothing is imported from these places into our 

 own country. It is said that Howland's Island is far from being 

 exhausted, and there is still left some guano of excellent quality 

 on Jarvis' Island, but it finds its way chiefly to the German market. 



Our main supply of material of this kind comes now from the 

 West Indies. Just at the mouth of the Gulf of Venezuela, in the 

 Caribbean Sea, lie great Curasao and little Curacao Islands. For 

 some years they have furnished large quantities of guano to Ger- 

 many and the United States. 



The little Cura9ao guano from which most of our supply comes 

 is poorer in phosphoric acid than the other, averaging from 25 to 

 28 ^. Its mechanical condition however is better. It is fine and 

 dusty with some hard lumps. Great Curagao guano goes largely 

 to Germany. It is hard and rocky but has from 38 to 42^ of 

 phosphoric acid, not over 2^ oxide of iron and alumina, and 

 some &fo carbonate of lime. 



Orchilla guano has a somewhat similar composition, though 1 

 believe it is of inferior value and importance. 



Another rock phosphate, the Navassa, is now extensively used 

 in this country as material for the superphosphate manufacture. 

 Probably it is not largely used in fertilizers which find their way 



