PHOSPHATES. 433 



PHOSPHATE OF AMMONIA. 



1. PREPARATION. 



(a.) By saturating pure phosphoric acid with ammonia. 



(b.) By decomposing, by carbonate of ammonia, the acidulous 

 liquor proceeding from the action of sulphuric acid upon bone ashes. 

 (See phosphate of lime.) 



2. PROPERTIES. 



(a.) Its crystals are rhombic prisms, terminated by dihedral sum- 

 mits ; the primary form is an oblique rhombic prism, whose smaller 

 lateral angle is 84, 30' ; sometimes it is obtained in needles. 



(b.) Its taste is sharp, cooling, and ammoniacal. 



re.) Sp. gr. 1.8051. 



(d.) Soluble in 4 parts of water at 60, and in less at 212; 

 crystallizes on cooling, but not beautifully, unless by spontaneous 

 evaporation. 



(e.) Not affected by the air. 



(/.) Suffers the aqueous fusion, and is decomposed by heat; the 

 ammonia is exhaled, and the phosphoric acid melts into a vitreous 

 globule. 



(g.) This is one mode by which the phosphoric acid is obtained 

 pure, or nearly so. 



(h.) On account of the facility with which this salt is decomposed 

 by heat, it affords phosphorus when heated with charcoal. 



3. COMPOSITION. Acid 28 -{-17 ammonia, or 62.22, and 37.78. 

 There is said to be also Ij equivalent of water.* 



4. MISCELLANEOUS. 



(a.) It exists in urine, mixed with the phosphate and muriate of 

 soda, from which it is difficult to free it ; in that state it forms the 

 long famed microcosmic salt. 



. (b.) In its pure state not employed; but the microcosmic salt has 

 been much used as a flux for the mineralogist, and in the composi- 

 tion of the pastes. 



BI-PHOSPHATE OF AMMONIA. 



1 . PREPARATION. By adding to phosphoric acid, ammonia or its 

 carbonate, till the solution ceases to precipitate muriate of baryta. 



2. PROPERTIES. Less soluble than the natural phosphate ; no 

 change in the air ; primary form, an octahedron, with a square base, 

 but the right square prism, with a rhombic base is most frequent.f 



3. COMPOSITION. Acid, 2 equivalents, 56+2 of ammonia, 34 

 + 3 of water, 27=117 for its equivalent. 



* Turner, quoting Mistcherlich. 

 t Turner. 



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