66 ■ CHEMICAL MANURES. 



solution, in special precipitation vats, taking care to stir, until a 

 slightly acid reaction ensues. There is thus formed crystalline 

 precipitate of acid phosphate of lime bicalcic. It is freed as- 

 completely as possible from the mother liquor, by filtration and 

 washing, which is greatly facilitated bv the solubility of the phos- 

 phates. The yield is very satisfactory, because only about 1 per 

 cent of the phosphate in the raw material remains in the solution.. 

 The latter, which contains a third of the amoant of lime originally 

 eliminated from the apatite, is mixed with the residual alkaline 

 cathode liquid, and the greater part of the lime is precipitated as 

 hydrate ; finally a current of carbonic acid gas is injected. After 

 precipitating the lime the solution is withdrawn and run into the- 

 electrolyzer. The electrolyte is thus continuously regenerated. 

 The product so obtained generally contains 86 to 38 per cent of 

 total phosphoric acid (the formula CaHPO^ + 2H.p requires 46-07 

 per cent of ^.Pr,). About 95 per cent of the phosphoric acid is 

 soluble in Petermann's solution of ammoniacal citrate of ammonia. 

 The composition of the product depends, moreover, on the amount 

 of lime in the raw material ; when it is rich in lime it requires a 

 greater amount of acid, and consequently of electric energy. There- 

 is a bye-product of slaked lime equal to 33 per cent of the bicalcic 

 phosphate formed. This process, which was the subject of several 

 years' laboratory work, was applied industrially last year [? 1909] in 

 an installation of 6 to 8 electric horse- power. One electric horse- 

 power can produce annually 20 cwt. of bicalcic phosphate soluble 

 in citrate, or 23 cwt. of 32 per cent. The cost of manufacture has 

 been provisionally estimated at 8-44: Swedish crowns per cwt. These 

 figures refer to an annual production of 2200 tons of bicalcic phos- 

 phate of 34 per cent. Comparative experiments on oats cultivated 

 in pots and continued for five years, show that the phosphate pre- 

 cipitated by electrolysis, provided that its composition responds 

 to that of bicalcic phosphate, exerts as energetic a fertilizing action 

 and as durable a one as superphosphate. The addition of important 

 amounts of carbonate of lime has not diminished the assimilability of 

 the former, whilst with tribasic phosphate the contrary is the result. 



