196 CHEMICAL MANUEES. 



sample is filtered from time to time, and tested with molybdate, or 

 phenol phthalein in the case of C^.^V.fl^. To work in a con- 

 tinuous fashion, two neutralizing vats are installed below the milk 

 of hme vat ; the latter is then fitted with two delivery pipes, which 

 are closed when need be by a cork stopper. When the contents. 

 of one of the vats is being neutrahzed, the second is being filled 

 with phosphate solution from the filter press. If excess of milk of 

 lime be added, it is easy to remedy it by running in phosphate 

 solution from the other vat. Finally, there is installed below the- 

 neutralizing vats a pit or collecting vat into which the neutralized 

 solution runs through a pipe fixed in the bottom of the two afore- 

 said vats. To neutralize the solution as exactly as possible, a milk 

 of lime of 15° B. = about 16 per cent CaO is used, of which enough 

 is added for the solution to remain faintly acid ; when the liquid is. 

 clarified it is decanted from the precipitate, and the neutralization 

 finished apart. The first precipitate is CaoH._,(POj2, the second i& 

 partly Ca3(P0J-. From the collecting vat the neutrahzed material 

 is draw^n by a suction and propelling pump and forced into a 

 Phillippe's washing filter press ; the precipitate is freed from adherent 

 calcium chloride by washing with water, followed by steam washing. 

 The precipitate filters well. The cakes extracted from the filter 

 press are dried at a temperature of 60° C. (140' F.) ; at the maximum, 

 best in the steam drying machine. 



They are converted into a fine friable powder containing 30 to- 

 40 per cent of 'P.,0^. At a higher temperature the CaoHo(POJ be- 

 comes slightly soluble. (Formation of PP-Cao.) When local facili- 

 ties lend themselves to it, the vats are installed in such a fashion 

 that they run from the one to the other. The last filter press for 

 the precipitate is then at a sufficient height for the cakes to fall 

 directly into a truck, which conveys them to the drier. The pre- 

 cipitated phosphate is soluble in a solution of citric acid. The- 

 manufacture of this product has been the object of numerous re- 

 searches and several patents.^ ' 



A precipitated phosphate manufactory requires : — 



1 ball mill. 



2 agitating vats. 



10 filter presses of 250 htres (55 gallons). 

 5 pumps. 



2 lime vats with stirrers. 

 2 collecting vats. 

 1 steam dryer. 

 4 pits with agitator, 2 metres x 2| metres. 



1 The whole subject was covered and exhausted, the filter press excepted., 

 by the numerous British patents of the 'sixties and 'seventies.— Ti*. 



