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phate rock, from the fossilized remains of extinct animals, 

 or from the soft phosphate deposits of tropical islands, and 

 quite recently large supplies of this element have been fur- 

 nished by the Thomas slag, a by-product of the Thomas- 

 Gilchrist steel process. In this country, for the past twenty- 

 five years, a large proportion of the phosphoric acid con- 

 sumed by our agricultural economy has been furnished by 

 the deposits of phosphate rock contiguous to Charleston, 

 S. C, but within more recent years the supplies of South 

 Carolina phosphate have been largely supplemented by the 

 soft phosphates from South Florida. 



The mechanical condition of fertilizers of all classes 

 greatly affects the utility and availability of their fertilizing 

 constituents, and in order to more readily meet the needs of 

 the plant the crude phosphate rock is crushed to a state of 

 impalpability, and the resulting powder so finely divided 

 that its particles can "float" in the air, is placed upon the mar- 

 ket under the name of "floats." 



Phosphates from some of the tropical islands of the Carib- 

 bean sea and adjacent waters are also utilized to some extent 

 as a source of phosphoric acid, though the deposits are be- 

 ing rapidly exhausted. 



The phosphatic formations of this character owe their 

 origin largely to the deposits of sea birds, and in rainless 

 climates nitrogen in the form of nitrates and ammonia salts 

 is also found, but in localities where the rainfall is at all con- 

 siderable, the proportion of this element is extremely small, 

 if it be not entirely absent. Large quantities of phosphor- 

 ic acid are also supplied from the wastes of our large 

 slaughter houses, and the fertilizers obtained from this 

 source contain also considerable proportions of nitrogen. 



Refuse bone black from the sugar refineries, after being 

 utilized for the decolorization of sugars, is frequently treated 

 with sulphuric acid and sold as a fertilizer under the name 

 of "dissolved bone-black," or else is used in the preparation 

 of many of our mixed fertilizers. 



The phosphoric acid in most of our complete fertilizers is 



