SULPHATES OF POTASH. 455 



is partially decomposed by that liquid, and deposits sulphate of 

 potash. It crystallizes from a strong solution in rhombohedral 

 crystals, of which the form is identical with one of the forms of 

 sulphur. But this salt is dimorphous and crystallizes from a 

 state of fusion by heat in large crystals, which have the form 

 of felspar (Mitscherlich.) It was the only bisulphate of potash 

 known before the unexpected discovery of another salt de- 

 scribed below. Its density is 2.163. The excess of acid in this 

 salt acts upon metals and alkaline bases, very much as if it 

 were free. 



Hydrated sesquisulphate of potash ; HO, SO 3 + 2 (KG, SO 3 ). 

 A salt in prismatic needles discovered by Mr. Phillips, and 

 which has also accidentally occurred since to M. Jacquelin. It 

 is decomposed by water; the circumstances necessary for its 

 formation are unknown. 



Anhydrous bisulphate of potash ; KO-f2SO 3 ; 1592.2 or 

 127.59. It appears, by M. Jacquelin's researches*, that this 

 salt almost uniformly presents itself when sulphate of potash, 

 and not less than one and a half equivalents of oil of vitriol are 

 dissolved together in distilled water, and the solution evapo- 

 rated. It crystallizes in prismatic needles, of which the den- 

 sity is 2.277; and point of fusion 410 (210 cent.) Left in 

 their mother liquor, these crystals gradually disappear, and in 

 their place^ large rhombohedral crystals of the hydrated bisul- 

 phate are formed. The anhydrous salt may be dissolved and 

 crystallized again from a quantity of hot water, not more than 

 sufficient for its solution, but is decomposed by a larger quan- 

 tity of water. This sulphate is analogous to the bichromate of 

 potash ; the constitution of these anormal salts has already been 

 made the subject of remark (page 328). 



Sulphate of potash combines with hydrated nitric and phos- 

 phoric acids, as well as with hydrated sulphuric acid. On dis- 

 solving the neutral salt in nitric acid, a little nitre and hydrated 

 bisulphate of potash are formed, with a large quantity of a salt 

 in oblique prisms, of which the formula is HO, NO 5 -f 2(KO, 

 SO 3 ). This last salt fuses at 302 (150 cent.); its density is 

 2.38 (Jacquelin). The compound with phosphoric acid is formed 

 by dissolving sulphate of potash in a syrupy solution of that 

 acid, and crystallizes in oblique prisms of six sides, which fuse 



* An. dc Ch. ct cle Ph. t. 70, p. 311. 



