432 PHOSPHATES. 



Dry phosphoric acid, 1 equivalent, 28 or 46.67 

 Soda, 1 " 32 or 53.33 



Its equivalent, 60 100.00 



In crystals ; Phos. acid, 1 equivalent, 28* 16.39 



Soda, 1 " 32 18.73 



Water, 12 " 108 64.88 



Its equivalent, 168 lOO.OOf 



According to Mr. Dalton's opinion, the salt above described is a 

 bi-phosphate, having 2 atoms of acid, and 1 of base, with double 

 the acid, making a quadro-phosphate it is neutral as to test colors. > 



To render the common or bi-phosphate neutral, Mr. Dalton says 

 that its sodaf must be doubled, when it will acquire much more sol- 

 ubility, and crystallize in fine needles. 



Mr. Dalton recommends this form of the salt as a test. Dr. Hen- 

 ry remarks, that fresh experiments are necessary to reconcile these 

 discordant statements.^ 



By heat on a sand bath, the crystals loose 12 equivalents of water, 

 without changing their properties. It is said that they still retain 

 an equivalent of water, which they give up at ignition ; and then 

 being redissolved in water, and the solution spontaneously evap- 

 orated, irregular four sided prisms are obtained, whose primary is a 

 rhombic octahedron ; they do not effloresce, are much less soluble 

 than before, and consist of 1 equivalent of acid, and 1 of soda, 

 with 5 of water. The solution precipitates nitrate of silver, white, 

 and not yellow, like the common phosphate. A phosphate of soda 

 has also been obtained, from a solution evaporated at 90, con- 

 taining 7 J equivalent of water ; they are permanent in the air, and 

 have a different form from the common phosphate. || 



4. MISCELLANEOUS. 



(a.) Exists in human urine, with phosphate of ammonia and, the 

 concrete salts, obtained by evaporation, are principally these two ; 

 formerly, under the name of microcosmic salt, much employed as a 

 flux, with the blowpipe. 



(b.) The phosphate of soda is used for the same purpose, and be- 

 sides its use in medicine, it is advantageously employed as a substi- 

 tute for borax in the soldering of metals. 



(c.) It is useful in chemistry ; by double exchange, we can thus 

 form almost all other phosphates. 



* 35.71, Mitscherlich, quoted by Turner, 2d Ed. p. 581. 



t Thomson's, First Prin. I, 201. 



t By adding as much again caustic soda. Turner, Vol. I, p. 568. 



{I Turner, 2d Edition, p 281, and Edin. Jour. XIV, No. p. 298. 



