that Salts are more soluble in hot than in cold Water. 21 



It is efflorescent, rapidly losing its watei* of crystallization 

 when exposed to the air, and falling down in a white powder. 



The crystals were drained, purified with great care by re- 

 peated agitation with water, and finally thrown upon a filter with 

 more water, and allowed to dry. Solutions were obtained by 

 occasionally agitating the salt with pure water during three or 

 four days, in the proportion of 2 ounces phosphate of magnesia 

 to 1 pint of water. The solutions were then decanted off and 

 filtered. Although the water drained from the crystals upon 

 the filter was nearly tasteless, yet the solutions thus obtained 

 were of a sweetish taste, which was sufficiently perceptible. 



A quantity of the solution, in the preparation of which dis- 

 tilled water only had been employed, was gradually heated by 

 immersion in the water-bath. Before the bath had arrived at 

 120°, the solution became turbid, and it assumed more and 

 more of a milky appearance as the heat increased, till the 

 temperature settled at 212°, when a cloudy precipitate slowly 

 subsided, and the supernatant liquid became nearly transpa- 

 rent. The precipitate was found not to differ in its sensible 

 properties from phosphate of magnesia deprived of its water 

 of crystallization. 



To determine the solubility of this salt at different tempe- 

 ratures, a solution was prepared by repeated agitation with 

 water, for more than a week, of a quantity of the salt from 

 which already three solutions had been derived. The tempe- 

 rature was about 45°. 



8000 grains of this solution, carefully filtered, were evapo- 

 rated to dryness on the sandbath. The residue was found to 

 be 10*75 grains anhydrous phosphate of magnesia. Hence 

 744 grains water dissolve 1 grain of the anhydrous salt. 



8000 grains of the same solution, in a glass stoppered phial, 

 were heated to 212° in the water-bath and retained for some 

 time at that temperature. When the precipitate had subsided, 

 a large portion of the transparent liquid was decanted off, and 

 the remainder with the precipitate thrown upon a filter while 

 still hot. It weighed when accurately dried 3'8 grains. Hence 

 8000 grains water at 212° retain in solution 10-75 — 3-8 = 6-95 

 grains ; or 1151 grains water retain in solution 1 grain of an- 

 hydrous phosphate of magnesia. Hence 1 part water dissolves 

 of anhydrous phosphate of magnesia, 



at 45° j\^; 



at 212° . ttVt- 



Of the hydrate, or phosphate of magnesia in the state of cry- 

 stals, 1 part water will therefore dissolve 



'■It 45 5^2 ; 



"I -^12^^ ^U' 



The 



