PHOSPHATES OF SODA. 475 



tion. If half an equivalent only of oil of vitriol is added, a 

 sesquisuJphate of soda is obtained in fine crystals, according to 

 Mitscherlich. 



Nitrate of soda; NaO, NO 5 ; 1067-9 or 85.57- This salt 

 crystallizes in the rhomboidal form of calc-spar. It is soluble 

 in twice its weight of cold water, and has a tendency to deli- 

 quesce in damp air. It burns much slower with combustibles 

 than nitrate of potash, and cannot therefore be substituted for 

 that salt in the manufacture of gunpowder. It is now gene- 

 rally had recourse to, as the source of nitric acid. Nitrate of 

 soda is found abundantly in the soil of some parts of India ; and 

 at Atacama in Peru, it covers large districts, from which it is 

 exported in considerable quantity. 



Chlorate of soda (NaO, C1O 5 ) is formed by mixing strong so- 

 lutions of bitartrate of soda and chlorate of potash, when the bi- 

 tartrate of potash precipitates, and the chlorate of soda remains 

 in solution. It crystallizes in fine tetrahedrons, and is consi- 

 derably more soluble than chlorate of potash. 



Phosphates of soda. There are three crystallizable phos- 

 phates of soda belonging to the tribasic class, which I shall de- 

 scribe under their old names. 



Phosphate of soda ; HO, 2NaO, PO 5 + 24HO; 4486.6 or 

 359.15.- This is the salt known in pharmacy as phosphate 

 of soda, and formed by neutralising phosphoric acid from 

 burnt bones (page 346) with carbonate of soda. It crystal- 

 lizes in oblique rhombic prisms, which are efflorescent, and es- 

 sentially alkaline. The taste of phosphate of soda is cooling 

 and saline, and less disagreeable than sulphate of magnesia, for 

 which it may be substituted as an aperient. It dissolves in 4 

 times its weight of cold water, and fuses in its water of crystal- 

 lization, when moderately heated. When evaporated above 90, 

 this salt crystallizes in another form with 1 4 instead of 24 atoms 

 of water (Clark). It is deprived of half its alkali by hydro- 

 chloric acid, but not by acetic acid. 



Subphosphate of soda ; 3Na O, PO 5 + 24HO ; 4?64.5 or 38 1 .78. 

 Formed when an excess of caustic soda is added to the preced- 

 ing salt. It crystallizes in slender six-sided prisms with flat 

 terminations, which are unalterable in air ; but the solution of 

 this salt rapidly absorbs carbonic acid, and is deprived of one- 

 third of its alkali by the weakest acids. The crystals dissolve 

 in 5 times their weight of water at 60, and undergo the watery 



