INTRODUCTION 7 



consideration of the following figures showing the output in 1920 

 of the various grades of basic slag. 



TABLE V. 



PRODUCTION IN 1920 



GRADE (in tons) 



1. Over 33 % CagPaOg 46,300 



2. 26-33% 121,400 



3. 22-26% , 90,900 



4. 15-22% , 302,500 



5. 11-15% 118,000 



6. Under 11%,, 22,000 



Total all grades 701,100 



The production of high grade basic slag, even if slag containing 

 only 33 % of phosphate is so classed, had fallen by 1920 to less than 

 one-tenth of the amount necessary to satisfy the demands of the 

 farmer, and it is probable that a comparatively short time will see 

 the last of this type of basic slag. 



Of the basic slags forming grades 3, 4, 5 and 6, a large proportion, 

 how large it would be difficult to say, are of low citric solubility due 

 to the use of fluorspar. It has been shown that the action of fluorspar 

 results in the replacement of the calcium silicate in the phosphate 

 compound of high soluble slags by calcium fluoride (19) and Bainbridge 

 has demonstrated that the resulting slag phosphate consists largely 

 of apatite (2). 



There are thus three types of slag available for agricultural purposes : 



1. High grade containing 16-20 % phosphoric acid. Part of this 

 supply consists of the rapidly diminishing remnants of the basic 

 Bessemer slags and the other part of the slags obtained from the 

 basic open hearth process by fractionating before the addition of 

 fluorspar. 



2. Open hearth basic slag containing 7 14 % phosphoric acid. 



3. Open hearth fluorspar basic slag containing 6 12 % of phos- 

 phoric acid. 



Numbers 1 and 2 have a citric solubility of 80-95 % whilst no. 3 

 has a citric solubility of from 6-50 %. 



Open hearth fluorspar basic slag is a new material containing 

 totally different phosphate compounds to those in nos. 1 and 2. It 

 is not the type of basic slag which produced the remarkable results 

 at Cockle Park and elsewhere. Its value compared with such slags 

 is unknown, and its low solubility suggests that it will prove less 

 effective as a fertiliser than the more soluble types. 



