448 POTASSIUM. 



oxygen of the salt is carried off as water, and the sulphur 

 remains in combination with potassium,, forming a fusible 

 compound "of a light brown colour. Sulphate of potash cal- 

 cined with one-fourth of its weight of pounded charcoal or pit- 

 coal, in a covered cornish crucible, at a bright red heat, is 

 converted into a black crystalline mass, which is also proto- 

 sulphuret of potassium, with generally a small quantity of a 

 higher sulphuret, arising from the combination of the silica of 

 the crucible with potash of the sulphate. If lamp-black be 

 used instead of charcoal, the sulphuret of potassium formed 

 having a great affinity for oxygen, and being in a highly divided 

 state, takes fire, when exposed to the air, and forms a pyro- 

 phorus. The solution of the protosulphuret in water is highly 

 caustic ; it is decomposed by acids with effervescence, from the 

 escape of sulphuretted hydrogen gas, but without any deposit 

 of sulphur. Being a sulphur base, it combines without decom- 

 position with sulphur acids. 



This sulphuret unites directly with sulphuretted hydrogen ; 

 and the same compound may be otherwise formed, namely, by 

 transmitting a stream of sulphuretted hydrogen through caustic 

 potash, so long as the gas is absorbed. It is often named the 

 bihydrosulphuret of potash. It is analogous in composition 

 to hydrate of potash in the oxygen series. 



The Tritosulphuret is formed when anhydrous carbonate of 

 potash, mixed with half its weight of sulphur, is maintained at 

 a tow red heat so long as carbonic acid gas comes off. Of four 

 proportions of potash, three become sulphuret of potassium, 

 while sulphuric acid is formed which neutralises the fourth pro- 

 portion of potash: 4KO and 10S = 3KS 3 and KO, SO ? . 

 With carbonate of potash and sulphur, in equal weights, a simi- 

 lar action occurs, at a temperature above the fusing point of 

 sulphur, but five, instead of three, proportions of sulphur then 

 unite with one of potassium, and a Pentasulpkuret is formed. 

 With a larger proportion of carbonate of potash the same sulphu- 

 ret is also produced, provided the temperature does not much 

 exceed the boiling point of sulphur, and the excess of carbo- 

 nate fuses along with it, without undergoing decomposition. 

 A sulphuret obtained by fusing sulphur and carbonate of potash 

 together has a liver-brown colour, and hence its old pharma- 

 ceutic name Hepar sulphuris. The three sulphurets described 

 are deliquescent, and are all soluble in water, the higher sul- 



