New York Agricultural Experiment Station. 69 



to 5 per cent, of iiitroo;en and from 20 to 25 per cent, of phosphoric 

 acid ; about one-third to one-fourth of the latter appears to be in 

 readily available condition. Raw bone-meal generally contains 

 somewhat more nitrogen (1 or 2 per cent.) and rather less phos- 

 phoric acid than steamed bone-meal. 



The fineness of the meal affects its value ; the finer the meal, the 

 more readily available is it as plant-food. On account of the in- 

 creased demand for bones for various purposes, and on account of 

 their increasing value, there is considerable tendency to adulterate 

 hone-meal with such substances as lime, gypsum, coal-ashes, ground 

 oyster-shells, ground rock -phosphate, etc. 



Phosphatic Guanos, or Rock-Guanos. — Guanos generally con- 

 sist chiefly of the dung of sea-fowls, though the term is applied to 

 other animal products. They are generally found in beds resembling 

 earthy deposits. The guanos which are called phosphatic contain 

 little or no nitrogen. Their phosphoric acid is generally in the form 

 of insoluble phosphate of lime, iron and alumina. These guanos 

 come mainly from certain islands in the Pacific ocean, and from 

 Caribbean sea and West India islands. The amount of phosphoric 

 acid in different guanos is very variable, ranging from below 15 to 

 over 30 per cent. 



Rock-Phosphates are known under several different names, 

 which generally designate the localities from which they come, as 

 South Carolina Rock, Florida Rock, Tennesee Rock, West India 

 Rock, etc. Other forms of mineral phosphates are known under 

 the names of Apatite, Coprolite and Phosphorite, which are found 

 in various places in America and Europe, and some of which are 

 used in making commercial fertilizers. However, the greatest 

 source of supply of j^hosphoric acid is the phosphate rock of our 

 Southern States. The rock-phosphates are extensively used in 

 making superphosphates. When ground to a very fine flour-like 

 powder, rock-phosphates are called " floats." Rock-phosphates con- 

 tain usually from 25 to 30 per cent, of phosphoric acid, and some as 

 much as 35 or 40 per cent. 



Superphosphates are known under several different names, 

 such as acid phosphate, dissolved bone, dissolved rock, dissolved 

 bone-black, etc. Superphosphates are formed by treating some 

 form of insoluble phosphate of lime, as rock-phosphate, bone, bone 

 ash, etc., with sulphuric acid. By this treatment there are formed 

 soluble phosphate of lime and gypsum (sulphate of lime) in nearly 



