CHLORIDE OF POTASSIUM. 4 -I. 1 ) 



phurets giving red solutions. They may indeed be prepared 

 by boiling sulphur, in proper proportions, with caustic potash. 

 A simultaneous formation of hyposulphurous acid then occurs, 

 as already explained (page 331.) The preparation, Precipitated 

 sulphur, is obtained by adding an excess of hydrochloric acid 

 to these solutions, when much sulphur is thrown down, although 

 the potassium be only in the state of protosulphuret, for the 

 sulphuretted hydrogen arising from the action of the acid on 

 that sulphuret, meets sulphurous evolved at the same time from 

 the decomposition of hyposulphurous acid, and these gases 

 mutually decompose each other, with the formation of water 

 and sulphur. The excess of sulphur in the alkaline sulphuret 

 also precipitates at the same time. The peculiar whiteness of 

 precipitated sulphur is owing, acording to Rose, to its containing 

 a little persulphuret of hydrogen. 



Chloride of potassium ; KC1; 932.6 or 74. 7 Formed by the 

 combustion of potassium in chlorine, or by neutralising hydro- 

 chloric acid by potash or its carbonate. It is also derived in 

 considerable quantity from kelp (page 384.) It crystallizes in 

 cubes and rectangular prisms, resembles common salt in taste, 

 is soluble in 3 times its weight of water at 60, and in less at 

 212. When pulverised and dissolved in 4 times its weight 

 of cold water, it produces a depression of temperature of 

 20j degrees ; while chloride of sodium, dissolved in the same 

 manner, lowers the temperature only 3.4 degrees. Upon the 

 difference between the two salts in this property is founded a 

 rude mode of estimating their proportions in a mixture. Chlo- 

 ride of potassium is principally consumed in the manufacture 

 of alum. 



Iodide of potassium; IK; 2069.4 or 165.82. This salt is 

 obtained by dissolving iodine in solution of potash till neutral, 

 evaporating to dryness, and heating to redness, to decompose 

 the portion of iodate of potash formed. It is more soluble than 

 the chloride, and may be obtained in cubes or rectangular 

 prisms, which are generally white and opaque, and have an alka- 

 line reaction from the presence of a trace of carbonate of potash. 

 The dry salt does not combine with more iodine, but in conjunc- 

 tion with a small quantity of water, (I believe 4 equivalents) it 

 absorbs the vapour of iodine with great avidity, and runs into 

 a liquid of a deep red, almost black, colour. According to 

 Baup, a saturated solution of iodide of potassium may dissolve 



c G 2 



