156 



CHEMICAL MANUEES. 



the phosphate was then run in and the agitator was wrought for 

 two to three hours. But that was bad working. Systematic manu- 

 facturing tests have led to the following conclusions : — 



1. The percentage of sesquioxides in the weak solution increases 

 with the length of the agitation and with the rise of temperature, 

 and the other impurities behave in the same way, HF, H.,SiF,;, CaO. 



2. The percentage of phosphoric acid in the insoluble residue 

 is least when the agitation only lasts about twenty minutes, from 

 that time onwards it decreases with the duration of the agitation, 

 "but in proportion to the oxide of iron content. There would appear 

 to be a retrogradation of the free phosphoric acid, dissolved under 

 the influence of the oxide of iron, as in superphosphates. 



3. The expenditure of sulphuric acid increases with the duration 

 of the agitation and the elevation of the temperature. Under 

 opposite conditions, the sulphuric acid content of the " weak solu- 

 tions " naturally decreases. These experiments were made in 

 •course of manufacture from Lahn phosphorite ; afterwards they 

 were generalized, especially for verifying the facts pointed out in 

 1 and 3, which are likewise applicable to Liege phosphate. The 

 results thus ascertained were applied immediately in industrial 

 practice. To diminish the duration of the mixing process was 

 •easily done : to lower the temperature of the mixing during working, 

 the sulphuric acid was diluted with the wash water and the hot 

 dilute acid passed through a tubular condenser, cooled by circulation 

 of water ; finally, to decompose the phosphate by sulphuric acid, half 

 quantities were taken. Great advantage arises from this style of 

 working, less handling, abolition of night work by installing of new 

 filter presses, economy of sulphuric acid, more complete extraction 

 of the phosphoric acid from the phosphates, longer life of the filter 

 cloths, and above all, obtaining a product richer in phosphoric 

 acid soluble in water. This product then had the following com- 

 position : — 



TABLE XLVII.— SHOWING THE ANALYSIS OF DOUBLE ST'PEK- 



PHOSPHATE. 



Monocalcic phosphate CaH^ 



(POJ, . . . . 

 Free phosphoric acid H-l'O^ 

 Dicalcic phosphate CaoH., 



(P0,)o . . " : 

 Tri basic phosphate C;;(P04)o . 

 Phosphate of iron and ahimina 



(FeAl)PO, 

 Hydrated pulphate of lime 



CaS0^2H,() 

 Macfne^ia, silica, Hnorine . 

 Sand, etc. .... 

 Moisture . . . . 



Per cent. 



(50-0 

 9-5 



4-.-) 



2 Ml 4S-1 per cent of total PoO-. 



4-U 43-3 per cent of P^.O., soluble in water. 



o-O 

 2-0 

 4-0 

 9-0 



100-0 



