POTASSIUM AND SODIUM. 209 



This is of course an expensive process, as potassium is a 

 costly metal. And, besides, this anhydrous oxide rapidly 

 becomes hydrated on exposure to common air by attracting 

 its moisture. The hydrate is a white solid. It has a soapy 

 feeling, owing to its dissolving the cuticle, forming with it a 

 kind of soap. It is a strong caustic, decomposing and dissolv- 

 ing the flesh, and making with it a soapy jelly. It eagerly 

 absorbs water from the air, and becomes dissolved in it. It 

 can therefore be kept in its solid state only by keeping it 

 shut in from the air. It can be dissolved in half its weight 

 of water. It has strong purifying powers, and hence is used 

 in making soap, which will be spoken of particularly in an- 

 other part of this book, when we show what the chemical 

 union is that it forms with fatty substances. This and the 

 other alkalies turn reddened litmus solution blue, as stated 

 in 80. 



287. How Potash is Obtained. Neither potassium nor po- 

 tassium hydrate occur native, but are always found com- 

 bined with acids forming salts, as potassium chloride, car- 

 bonate, nitrate, etc. Thus combined it is a very abundant 

 substance in nature. Potassium carbonate abounds in veg- 

 etables, and the name potash comes from the pots in which 

 the vegetables from which it was obtained used formerly to 

 be burned, the alkaline carbonate remaining with the ashes 

 at the bottom of the pots. It is from this carbonate that 

 the caustic potash is ordinarily obtained. The carbonic 

 acid can not be driven off by heat, but it can be taken away 

 by some substance which has a stronger affinity for it than 

 the potash has. Such a substance is lime. This added to 

 a solution of potassium carbonate in proper quantity takes 

 the carbonic acid, forming calcium carbonate, and leaves 

 the potassium hydrate free in solution. On evaporating 

 this solution, by heating it in a basin of iron, we obtain 

 caustic potash : 



