MANUFACTUEE OF BONE SUPEEPHOSPHATE. 195 



requires a slight excess of lime to form an insoluble phosphate — one 

 part P.>05 requires 0*4 of CaO, as the following equations show : — 



CaH,(POj^^H.,0 + CaO + H.,0 = Ca,H,(POJ,2H.O 

 CaH,(POj^H;0 + 2CaO ' = CaSPASH^O 



To prepare the acid phosphoric solutions, a wooden vat is fitted 

 with a mechanical agitator also of wood. No mechanical agitator is 

 required working with bones. The bones are covered completely 

 by an 8 per cent solution of hydrochloric acid, and left in contact 

 for two to three days. All the mineral matter is dissolved, whilst 

 the ossein, a white soft substance, remains undissolved. The 

 benzine fat-extracted bones decompose more easily than steamed 

 bones. The decomposition is ascertained to be finished when a 

 hollow bone placed at the surface as a sample is soft and supple, 

 and shows well the characteristics of swollen ossein. The solu- 

 tion is then run off through a tap in the bottom of the vat, the 

 ossein is washed with the smallest possible amount of 4 per cent 

 hydrochloric acid, and the liquid is collected in a tank. The 



lait de cbau 



6ac 

 de precijailafior 



1 



Vi 



ac 

 coliecteuf 



jL=^ \A/ajcn 



Fig. 87. — Plant for Manufacture of Precipitated Phosphate of Lime. 



Lnit de cliaux — Milk of Lime. Bac de precipitation = Precipitation Vat. 



Pompc = Pump. 



Bac collecteur — Collecting Vat. 



wash water is used afterwards to dilute the strong hydrochloric 

 acid, that is why a more methodical extraction is not pursued. As 

 to the quantity of hydrochloric acid, a little more than the theo- 

 retical quantity calculated on the lime must be used. When the 

 phosphate is finally ground, solution is effected in ten to fifteen 

 minutes ; it is pumped into a filter press by means of a pump with 

 lead armature. The phosphatic solution is collected in an open 

 lead-lined vat, not too deep, in which it is neutralized by milk of 

 lime. To precipitate the Ca^HoPO^, milk of lime, in quantity just 

 sufficient to neutralize the free HCl, is added, the HCl used, 

 and the phosphoric acid content of the substance must be known, 

 then one molecule of CaO for each molecule of CaH^P.^Og. For 

 this purpose there is installed on a level with the top of the 

 neutralizing vat, a second lead-lined vat fitted with a tap 15 cm. 

 above the bottom, in which a milk of lime is prepared, which is run 

 into the neutralizing vat, care being taken to stir the mixture in the 

 latter. To make sure that enough milk of lime has been added, a 



