PHOSPHORUS. 109 



15. PHOSPHOEUS. 

 Piii = 31 (30 96). 



Occurrence in nature. Phosphorus is found in nature chiefly in 

 the form of phosphates of calcium (apatite, phosphorite), iron, and 

 aluminum, which minerals form deposits in some localities, but occur 

 also diffused in small quantities through all soils upon which plants 

 will grow, phosphorus being an essential constituent of the food of 

 most plants. Through the plants it enters the animal system, where 

 it is found either in organic compounds, or and this in by far the 

 greater quantity as tricalcium phosphate principally in the bones, 

 which contain about 60 per cent, of it. From the animal system it 

 is eliminated chiefly in the urine. 



Manufacture of phosphorus. Phosphorus was discovered and 

 made first in 1669 by Brandt, of Hamburg, Germany, who obtained 

 it in small quantities by distilling urine previously evaporated and 

 mixed with sand. 



The manufacture of phosphorus to-day depends on the deoxida- 

 tion of metaphosphoric acid by carbon at a high temperature in 

 retorts. 



The acid is obtained by adding to any suitable tricalcium phophate sulphuric 

 acid in a quantity sufficient to combine with the total amount of calcium 

 present. The first action of sulphuric acid upon the phosphate consists in a 

 removal of only two-thirds of the calcium present, and the formation of an 

 acid phosphate : 



Ca 3 (PO 4 ) 2 + 3H 2 SO 4 = CaH 4 (PO 4 ) 2 + 2CaSO 4 + H 2 SO 4 . 



The nearly insoluble calcium sulphate is separated by filtration, and the 

 solution of acid phosphate containing free sulphuric acid is evaporated to the 

 consistency of a syrup, when more calcium sulphate separates and a solution 

 of nearly pure phosphoric acid is left : 



CaH 4 (PO 4 ) 2 + H^O, == CaS0 4 + 2(H 3 PO 4 ). 



This syrupy phosphoric acid is mixed with coal and heated to a temperature 

 sufficiently high to expel water and convert the ortho- into meta-phosphoric 

 acid: 



2(H 3 PO 4 ) = 2HP0 3 + 2H 2 O. 



The dry solid mixture of this acid and charcoal is now introduced into 

 retorts and heated to a strong red heat, when the following decomposition 

 takes place : 



2(HPO 3 ) + 5C = H 2 O + 5CO + 2P. 



The three products formed escape in the form of gases from the retort, and by 

 passing them through cold water phosphorus is converted into a solid. The 

 reaction in the retorts is somewhat more complicated than above stated in the 



