TJie Phosphates of America. 129 



Selecting an acid strength of 50 B. for our illustration, we 

 shall find that our sum will work out thus : 



55 Ibs. phosphate of lime X 1 . 517 = 83 . 44 Ibs. vitriol of 50 B. 



3.50 " carbonate of lime X 1.565= 5.48 " " " 



6.50 " phosphate of iron and alumina X 1.930 = 12. 55 " " " 



0.75 " carbonate of magnesia X 1.860= 1.40 " " " 



2.25 " fluoride of lime... ...X2.010= 4.52 " " " 



Total sulphuric acid of 50 B. strength re- 

 quired for every 100 pounds of the above 

 phosphate 107.39 Ibs. 



The decomposition of the raw material is effected in large wood- 

 en tanks made of suitable wood and provided with wooden agitators. 



2147 pounds 60 B. sulphuric acid are run into each tank and 

 diluted with water until its strength is reduced to 14 B. The 

 agitators are now set in active motion, and 2000 pounds of the phos- 

 phate, finely ground as directed for superphosphate manufacture, 

 are slowly added and the stirring is continued for five hours. Open 

 steam is occasionally blown in by an injector through the side of 

 the tank, in order to keep up the temperature of the mixture. 



At the end of the specified time the cream from each tank is 

 run off into filters large wooden vessels lined with lead and pro- 

 vided with false bottoms. 



The hydrated sulphate of lime here separates from the solution 

 of phosphoric acid, the latter passing through the filter as a bright 

 straw-colored fluid, of a gravity which, at first, is about 12 B., 

 but which gradually gets reduced by careful washing to 1 B. 



By the exercise of ordinary care and precautions, all cracks on 

 the surface of the gypsum contained in the filters may be avoided, 

 for were they to be formed, too ready an outlet would be afforded 

 for the washing-water. The washing is stopped directly the grav- 

 ity reaches 1 B., and the hydrated sulphate of lime is first piled 

 up in the centre of the filters to drain, and is then carried to the 

 dump ; the last runnings from the filters, which are too weak for 

 economical concentration everything under 5 B. being used to 

 dilute the sulphuric acid in subsequent operations. 



If the wooden tanks be put up on the large scale in series of 

 ten, a batch of the emulsion can be discharged from them, one 

 after the other, every half-hour, when once they are all in proper 

 working order, and in this manner twenty tons of phosphate can be 

 treated per day. 





