454 POTASSIUM. 



purposes by igniting bitartrate of potash, or better by bunr.ng 

 together 2 parts of that salt and 1 of nitre. In the latter pro- 

 cess the carbon and hydrogen of the tartaric acid are destroyed 

 by the oxygen of the nitric acid, and carbonate of potash re- 

 mains mixed with charcoal, from which it may be separate_d by 

 solution and filtration. 



Carbonate of potash has an acrid, alkaline taste, but is not 

 caustic. It gives a green colour to the blue infusion of cabbage. 

 This salt is highly deliquescent, and soluble in less than an 

 equal weight of water at 60. It may be crystallized with two 

 equivalents of water. Added to solutions of salts of lime, lead, 

 &c., it throws down insoluble carbonates. It is more fre- 

 quently used than the caustic alkali, to neutralise acids and to 

 form the salts of potash. 



Bicarbonate of potash ; HO, CO 2 + KO, CO 2 ; 1255.3 or 

 100.61. Formed by transmitting a stream of carbonic acid gas 

 through a saturated cold solution of the neutral carbonate. It 

 is soluble in four times its weight of water at 60, and in less 

 water at 212. The solution has an alkaline taste and reaction, 

 but is not acrid ; it does not throw down magnesia from its 

 soluble salts ; it loses carbonic acid when evaporated at all tem- 

 peratures, and becomes neutral carbonate. The salt contains 

 one proportion of water, which is essential to it, and crystal- 

 lizes well in prisms of eight sides, having dihedral summits. 

 The existence of a sesquicarbonate of potash is doubtful. 



Sulphate of potash; KO, SO 3 ; 1091.1 or 87.43. This salt 

 precipitates when oil of vitriol is added drop by drop to a con- 

 centrated solution of potash. It is generally prepared by neu- 

 tralising the residue, composed of bisulphate of potash, of the 

 nitric acid process, (page 292), and crystallizes in double pyra- 

 mids of six faces, or in oblique four-sided prisms. The crystals 

 are anhydrous, unalterable in air, arid they decrepitate strongly 

 when heated ; their density is 2.400. The sulphate is one of 

 the least soluble of the neutral salts of potash; 100 parts of 

 water dissolve 8.36 parts of this salt at 32, and 0.09666 parts 

 more for each degree above that point. 



Hydrated bisulphate of potash, or Sulphate of water and po- 

 tash; HO, SO 3 + KO, SO 3 ; 1704,7 or 136.59. The fusible salt 

 remaining when nitrate of potash is decomposed in a retort by 

 two equivalents of oil of vitriol. Below 386.6 (197 cent.), it is 

 a white crystalline mass. This salt is very soluble in water, but 



