838 ANNUAL REPORT OF THE Off. Doc. 



are six grades of bone tankage recognized in the trade: 1st grade, 

 containing 18 or 19 per cent, of phosplioric acid; 2d grade, 16 per 

 cent, phosphoric acid; 3d grade, 13^ per cent, phosphoric acid; 4th 

 grade, 11^ per cent, phosphoric acid; 5th grade, 9 per cent, phosphoric 

 acid, and 6th grade, 7 per cent, phosphoric acid. The nitrogen of 

 tankage increases as the percentage of phosphoric acid decreases. 



OTHER ORGANIC SOURCES OF PHOSPHORIC ACID. 



There are numerous other sources of phosphoric acid which may 

 all be included in the class of refuse or by-product materials. Dried 

 fish, which contains about 7 or 8 per cent, of phosphoric acid, is the 

 most important of this class. Cottonseed meal and castor pomace 

 are also important sources of phosphoric acid. 



PHOSPHATIC GUANO. 



There are two classes of phosphatic guanos; those which are 

 largely lime phosphates and another class which are largely iron 

 and alumina phosphates. Both these classes are called guanos 

 because they resemble one another very closely in general appear- 

 ance, and were probably of the same origin. These guanos were 

 formed from the dung of birds. The Peruvian guano was the first 

 to come into general use and it gave remarkably good results, but 

 it contained some nitrogen and potash, as well as phosphoric 

 acid. The other phosphates of this class, while resembling the 

 Peruvian guano much in appearance, yet were formed in rainy 

 regions, which w'ashed out the nitrogen and potash of the original 

 dung. The following are the principal phosphate of lime guanos: 

 Baker Island guano, which contains 65 to 85 per cent, of lime; How- 

 lands Island and Jarvis Island are both nearly as good. These three 

 islands are in the Pacific ocean. Majellones and Patagonia phos- 

 phates are both rich in phosphate of lime, and also contain some 

 nitrogen. The Mona Island, Navassa and Orchilla guanos contain 

 considerable phosphate of lime, but also have a marked per cent, 

 of iron and alumina phosphates, which places them in the latter 

 class as far as their value for manufacturing purposes is con- 

 cerned. 



(2) IRON AND ALUMINA PHOSPHATES. 



Very large deposits of phosj)hates of iron and alumina have been 

 discovered in many places of the West India Islands. They were 

 at first mistaken and shipped in large quantities for phosphate of 

 lime. Upon complete analysis their true nature was determined, 

 and because they were unsuitable for the manufacture of super-phos- 

 phates, giving, when treated with sul])hnri(' add. a sticky mass 



