210 CHEMISTRY. 



Potassium ^ i v j t Calcium Potassium 



carbonate. Calcmm W ie ' carbonate. hydrate. 



K 8 CO 3 + CaII 2 O 3 CaC0 3 + 2(KHO) 



The same thing is done in part in the common leach-tubs. 

 Lime is put into the lower part of the tub, so that as the 

 dissolved carbonate of potash comes down a part of it is 

 deprived of its carbonic acid, and therefore becomes caustic 

 potash. The lye thus produced is then a solution of the 

 caustic potash and the carbonate together. 



288. Potassium Carbonate, K 2 CO 3 . If a lye be obtained 

 from wood-ashes, and be evaporated to dryness, we .have in 

 the mass which is left the common crude potash of com- 

 merce. There are in this many impurities mingled with the 

 potassium carbonate, for there are other soluble salts in the 

 ashes which appear in the lye. Pearlash is this common 

 potash partially purified from these impurities. Potassium 

 carbonate is decidedly alkaline, having an alkaline taste, 

 and turning red litmus paper blue. It has to some little 

 extent the cleansing power of caustic potash. Though quite 

 insoluble in alcohol, it is very soluble in water, though not 

 so much so as potassium hydrate. It dissolves in twice its 

 weight of water, while potassium hydrate requires only half 

 its weight of water to dissolve it. It is a very deliquescent 

 salt, and therefore to preserve it dry it must be kept in well- 

 stopped bottles. 



289. Experiment. You learned in 287 that although no 

 degree of heat can drive away carbonic anhydride from po- 

 tassium carbonate, it can be taken away by a substance 

 which has a stronger affinity for it than potassium has, as, 

 for example, lime. It can also be driven off by any acid 

 stronger than carbonic acid. Such an acid we have in 

 acetic acid, the acid of vinegar, as may be shown by the 

 simple experiment represented in Fig. 87 (p. 211). Put a 

 teaspoonf ul or more of pearlash into a tumbler containing 



