220 NON-METALS AND THEIR COMBINATIONS. 



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 : 



CagCPOJa + 3HaSO 4 = CaH 4 (PO 4 ) 2 -f 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 phosphorig acid is left : 



CaH 4 (PO 4 ) 2 + H 2 SO 4 = CaS0 4 -f 2(H 3 POJ. 



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 POJ = 2HPO 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(HP0 3 ) + 50 = H 2 + SCO + 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 

 equation, as some gaseous hydrogen phosphide and. a few other products are 

 formed in small quantities. 



Also phosphorus is now made by subjecting to the action of a strong electric 

 current a mixture of tricalcium phosphate and carbon, when phosphorus is set 

 free, while calcium carbide and carbonic oxide are formed : 



Ca,(PO 4 ) 2 + 140 = 2P + 3CaC 2 -4- SCO. 



Properties of phosphorus. When recently prepared, phos- 

 phorus is a colorless, translucent, solid substance, which has some- 

 what the appearance and consistency of bleached wax. In the 

 course of time, and especially on exposure to light, it becomes by 

 degrees less translucent, opaque, white, yellow, and finally yellowish- 

 red. At the freezing-point phosphorus is brittle ; as the temperature 

 increases it gradually becomes softer, until it fuses at 44 C. (111F.), 

 forming a yellowish fluid, which at 290 C. (554 F.) (in the absence 

 of oxygen) is converted into a colorless vapor. Specific gravity 1.83 

 at 10 C. (50 F.) 



The most characteristic features of phosphorus are its great affinity 

 for oxygen, and its luminosity, visible in the dark, from which 



