POTASH. 447 



strongly, and soonest upon the line>s, which have been described 

 on the glass by the stirrer. A similar precipitation is occa- 

 sioned in salts of potash by hy perchloric acid. Also by chlo- 

 ride of platinum, which forms the double chloride of platinum 

 and potassium, in granular octohedrons of a pale yelbw colour. 

 In the separation of potash,, for its quantitative estimation, the 

 last reagent is preferred, and is added in excess to the potash 

 solution, together with a few drops of hydrochloric acid, which is 

 then evaporated by a steam heat to dryness. Water with an 

 admixture of alcohol is digested upon the dry residue, which 

 dissolves up every thing except the double chloride of platinum 

 and potassium. Ammonia is also thrown down by chloride of 

 platinum ; but when the chloride of platinum and ammonium 

 is heated to redness, nothing is left except spongy platinum, 

 while the chloride of platinum and potassium leaves all its po- 

 tassium in the state of chloride mixed with the platinum. 

 Potash is likewise separated from acids, by means of fluosilicic 

 acid, which throws down a light gelatinous precipitate, the 

 double fluoride of silicon and potassium. 



Potash is the base which in general exhibits the highest affi- 

 nity for acids ; it precipitates lime and the insoluble metallic 

 oxides from their solutions in acids. This alkali is employed 

 indifferently with soda for a variety of useful purposes. The 

 principal combinations of potash with acids will be described 

 after the binary compounds of potassium. 



Peroxide of potassium, KO 3 . Heated strongly in air or oxy- 

 gen, potassium combines with three equivalents of oxygen. 

 The ultimate residue on calcining nitrate of potash at a red 

 heat has been said to be the same compound, but Mitscherlich 

 finds that residue to be potash. The peroxide of potassium is 

 decomposed by water, being converted into hydrate of potash, 

 with evolution of oxygen gas. 



When potassium is burned with an imperfect supply of air, 

 a grey matter is formed, which Berzelius believes to be a sub- 

 oxide of potassium. It is not more stable than the peroxide. 



Sulphurets of potassium. Sulphur and potassium, when 

 heated together, unite with incandescence, and in several pro- 

 portions, two of which correspond respectively with the protox- 

 ide and peroxide of potassium. The proto sulphur et may be 

 obtained by transmitting hydrogen gas over sulphate of potash, 

 heated in a bulb of hard glass to full redness^ when the whole 



G G 



