436 PHOSPHATES. 



(6.) The fluid obtained by the filtration is acidulous phosphate and 

 acidulous sulphate of lime;* the two neutral salts being held in solu- 

 tion by an additional quantity, probably an equivalent of their respec- 

 tive acids. To free the fluid from the earthy matter thus dissolved, 

 the liquor may be decomposed by acetate or nitrate of lead, and the 

 precipitate of phosphate of lead may be decomposed by heating it 

 in an earthen retort, with half its weight of charcoal powder. The 

 phosphorus, obtained in this way, may be contaminated with sulphur, 

 because sulphate of lead is thrown down by the acetate or nitrate ; 

 this may be got rid of, by decomposing the phosphate of lead by sul- 

 phuric acid, and then the liberated phosphoric acid by charcoal. 



(c.) This process is complicated, and it is better to decompose the 

 .acidulous phosphate by adding carbonate of ammonia; the phosphate 

 of ammonia, on being evaporated and heated to low redness, gives 

 up its ammonia ; sulphate of ammonia, if present, is volatilized, and 

 the phosphoric acid is obtained nearly or quite pure. But even this 

 is unnecessary, if the object is merely to obtain the phosphorus ; for 

 that purpose the acidulous phosphate may be at once decomposed. 



(d.) The purified acid, mixed ivith one half its weight of charcoal 

 powder and heated in a furnace, affords about one fourth of its iveight 

 of phosphorus.^ 



(e.) The solid residuum from (b) is commonly employed to afford 

 phosphorus. 



(/.) It is mixed with from J to J its weight of dry powdered char- 

 coal and distilled. 



(g.) The acidulous solution, when considerably evaporated, must 

 be suffered to cool, and sulphate of lime will subside, which must be 

 separated. 



(A.) The earthen retort is glased with lime, 1 part, slacked ivith a 

 solution of 2 parts of borax; and with this mixture the retort is wash- 

 ed thoroughly, inside and out ; when it is heated it will melt and fill 

 the pores through which the phosphorus would otherwise escape. 



(i.) The retort is carefully coated with fire lute, and its neck dips 

 into water ; the heat is very gradually raised, and much gas is pro- 

 duced ; it burns spontaneously, with brilliant flashes ; we continue 

 the heat some time after gas has ceased to come. 



(/.) If the neck of the retort is choked, which is ascertained by a 

 wire, a hot iron bar is applied to it externally to melt the phosphorus. 



(/c.) Some phosphorus may come over into the water, but most 

 of it condenses in the neck of the retort, and must be got out by 

 heating it with water poured from a tea kettle. 



* Perhaps bi-phosphate and bi-sulphate. 



t It is said not to be so good for (his purpose as the acidulous phosphate, because- 

 it is more liable to be volatalized. 



