116 The Phosphates of America. 



Total phosphoric anhydride soluble in hydrochloric acid. . .18.93 

 Of which there was found to be 



Water-soluble phosphoric anhydride 15 .03 



Citrate-soluble " " 17.01 



Unless our conclusions are ill-founded in every particular, these 

 figures and details confirm the position we have assumed. 



In the first place, they prove that raw mineral phosphates con- 

 taining a fair proportion of carbonate of lime may carry a high 

 percentage of iron and alumina and yet 'yield a perfectly dry and 

 pulverulent product, in which nearly all the phosphoric acid is in 

 a readily soluble or available form. As a necessary consequence, 

 while this amount of carbonate certainly calls for an increased 

 outlay of sulphuric acid and thereby adds somewhat to the cost of 

 manufacture, it is, nevertheless, in the end a source of the truest 

 kind of economy and profit. 



In the second place, they prove what we have never ceased to 

 claim, that the prevalent custom of calcining Florida phosphates is 

 unscientific and harmful, and that whereas the production of a dry 

 and porous " super " always follows the use of carbonate, the pres- 

 ence of free lime always retards the drying action. 



In the third place, they prove the necessity for complete chemical 

 analysis of the raw material, and demonstrate the utter worthless- 

 ness of analytical reports which merely give the percentage of total 

 phosphoric acid, calculated to its equivalent of tricalcic or "bone" 

 phosphate. What kind of iron and steel would be produced, if 

 those concerned in that industry were content to know the mere 

 percentage of metallic iron contained in a sample of iron ore ? 



Turning now from the purely chemical, to that side of the 

 industry which calls for mechanical details, we come first to the 

 operation of grinding the raw phosphate, and we may be allowed 

 to say that this is a matter for the most serious attention. 



A growing recognition of the necessity for extremely fine 

 grinding is one of the most satisfactory results of scientific teach- 

 ings, and we are glad to see that progressive manufacturers now ad- 

 mit it to be the only means of attaining high dissolving efficiency. 



In proportion to the natural hardness of the phosphate rock 

 this necessity for fine separation of the particles increases, and it 

 has been the experience, with Canadian apatites for example, that 

 unless the material is so disintegrated as to pass freely through a 

 70 or even an 80 mesh screen, it is only very slowly and incom- 

 pletely acted upon by 50 B. sulphuric acid. 



