430 PHOSPHATES. 



(d.) Soluble in nitric and phosphoric acid, without effervescence, 

 and precipitated from that solution by lime water or ammonia. 



(e.) Sulphuric acid decomposes them, at least in part, and sepa- 

 rates the phosphoric acid. 



(/.) Often phosphoresce by heat. 



Form bi-phosphates and some triple salts. 



Those of the alkalies, soluble ; of the earths, insoluble. 



PHOSPHATE OF POTASSA. 



1. PREPARATION. 



Sa.) In the mode soon to be mentioned for the phosphate of soda. 

 b.) By heating the bi-phosphate in a platinum crucible, along with 

 pure potassa. 



2. PROPERTIES. 



(a.) Insoluble in cold, but soluble in hot water ; " it precipitates 

 as the solution cools in a brilliant gritty powder." Very fusible 

 producing before the blowpipe a transparent bead opake on cooling, 

 Forms a " thick, glutinous and adhesive" solution in muriatic, nitric, 

 and phosphoric acids ; alkalies occasion no precipitate from these 

 solutions, if much diluted ; otherwise, the reverse. 



The vegetable grains belonging to the Cerealia, contain a small 

 quantity of this salt. 



It is supposed to be a compound of 1 equivalent of water, 2 of 

 acid, and 1 of alkali. 



It is said that a subphosphate of potassa is obtained by fusing po- 

 tassa and phosphate of potassa together, in a platinum crucible. 



It is insoluble in cold, but sparingly soluble in hot water. It is 

 supposed that it has two equivalents of potassa and 1 of acid, while 

 the neutral phosphate contains one equivalent of each constituent, and 

 the bi-phosphate, 2 of acid to 1 of alkali. 



Bl-PHOSPHATE OF POTASSA. 



1. PREPARATION. Formed by dropping liquid phosphoric acid 

 into carbonate of potassa, till effervescence ceases, and the liquid 

 ceases to precipitate muriate of baryta. 



2. PROPERTIES. 



(a.) By evaporation crystallizes in square prisms ; the primary 

 form, an octahedron with square bases. The composition is, 1 

 equivalent of potassa, 2 of phosphoric acid, and 2 of water. 



(b.) Very soluble in water; taste bitter; sp. gr. 2.8516; by 

 heat, melts and loses its water ; becomes dry, and again deliquesces. 

 At ignition, melts into a transparent deliquescent glass. Exists in 

 small quantities in barley.* 



* Hope. Note Book. 



