70 Report of the Acting Director and Chemist of the 



equal proportioris. Owing to their comparative cheapness and 

 abundance, rock-phosphates are more often used in. making super- 

 phosphates than bones, bone-ash or bone-black. The value of a 

 superpliosphate depends upon the amount of soluble phosphate of 

 lime present in it together with the amount of reverted phosphate 

 of lime. The amount of sohible phosphoric acid compounds in 

 superphosphates varies with the kind of phosphate used in making 

 superphosphate, and also with other conditions whicli we need not 

 mention here. Good quality of dissolved bone contains 12 to 18 

 per cent, of soluble phosphoric acid. Dissolved bone-black contains 

 from below 15 to over 17 per cent, of soluble phosphoric acid. 

 Superphosphate made from rock-phosphate may contain from 12 to 

 18 per cent, of soluble phosphoric acid. 



Thomas Slag is more familiarly known as odorless phosphate. 

 It is also known under several other names, such as basic iron slag, 

 Thomas scoria, phosphate slag, etc. This is a comparatively new 

 source of phosphoric acid compounds. It is a by-])roduct formed in 

 the manufacture of iron and steel from certain kinds of iron ore 

 containing phosphorus compounds. In the process phosphate of 

 lime is formed, which is ground to a fine powder. Odorless phos- 

 phate is insoluble in water but is somewhat soluble in ammonium 

 citrate solutions and its phosphoric acid is, therefore, available to 

 some extent. The samples of odorless phosphate which we have 

 analyzed at this station generally contained between 19 and 20 per 

 cent, of total phosphoric acid, with 6 to 7 per cent, of available 

 phosphoric acid. The practical results coming from the use of this 

 form of phosphoric acid compounds have been varied, often being 

 most excellent and again very indiiferent. 



In the table following, we give the amounts of different forms of 

 phosphoric acid found in different phosphate materials : 



