8 CHEMICAL MANURES. 



the excitation of the nervous centres which it produces. Its anti- 

 dote is spirits of turpentine. The vapours of phosphorus frequently 

 respired induce necrosis of the bones, chiefly those of the face. The 

 ordinarv phosphorus industry and the manufacture of matches are 

 amongst the most unhealthy of unsanitary trades. Chemical Pro- 

 perties. — (2j Ordinary phosphorus oxidizes slowly in the air, and this 

 oxidation is accompanied by a phosphorescent glow, from which 

 phosphorus takes its name. Its suffices, moreover, to cut it with a 

 knife to inflame it, by the heat produced by the friction ; that is 

 whv it should be cut under water. Chemically combined oxygen 

 exercises on phosphorus the same oxidizing action as free oxygen. 

 Water, which is a very stable compound of oxygen and hydrogen, 

 is destroyed, though slowly, by this body with formation of phos- 

 phoric acid and phosphoretted hydrogen. The transformation is 

 more rapid when the water is rendered alkaline by caustic potash, 

 soda, or lime. Nitric acid oxidizes phosphorus very energetically, 

 converting it mostly into phosphoric acid. Owing to its great 

 affinity for oxygen, phosphorus is not found in nature in the free 

 state, it is always met with as phosphoric acid combined with 

 bases. 



Oxygenated Compounds of Phosphorus. — Phosphorus forms 

 with oxvgen and hvdrogen the following anhydrides and acids : — 



Hypophosphorous acid ... 

 Phosphorous acid .... 

 Phosphoric acid .... 



There are three phosphoric acids known, viz. :- — 



Metaphosphoric acid H.,OP.,0, = HPO., 

 Pyrophosphorie acid 2HoOP.,6, = H^P-.O; 

 Orthophosphoric acid .3H..OP.,6- = H-PO^ 



Hypophosphorous acid is monobasic, that is to say, only one of its 

 atoms of hydrogen can be replaced by a metallic atom. Phos- 

 phorous acid is dibasic, and phosphoric acid tribasic. There are, 

 therefore, three phosphoric acids, which differ in the fact that one, 

 two, or three atoms of H may be replaced by as many basic atoms. 

 It is to Graham that we owe the discovery of their characteristic 

 reactions. Metaphosphoric acid only gives one species of meta- 

 phosphate. Pyrophosphorie acid gives two species of pyrophos- 

 phates. Orthophosphoric acid gives three species of salts corre- 

 sponding to the formulae M._,PO, ; M.,HPO^ ; MH.PO,. These acids 

 are distinguished the one from the other by the following reaction : 

 the meta acid gives a white precipitate, with barium chloride and 

 silver nitrate, and .coagulates a solution of albumen ; the pyro acid 

 gives no precipitate with barium chloride, gives a white precipitate 

 with silver nitrate, and does not coagulate albumen ; the ortho acid 



