144 SOW CROPS GROW. 



THE CARBONATES which occur in the ashes of plants 

 are those of Potassium, Sodium, and Calcium. The 

 Carbonates of Magnesium, Iron, and Manganese are de- 

 composed by the heat at which ashes are prepared. 



Potassium Carbonate, or Carbonate of Potash, 

 K 2 C0 3 , 114. The pearl-ash of commerce is a tolerably 

 pure form of this salt. When wood is burned, the potash 

 which it contains is found in the ash, chiefly as carbon- 

 ate. If wood-ashes are repeatedly washed or leached with 

 watei', all the salts soluble in this liquid are removed ; by 

 boiling this solution down to dryness, which is done in 

 large iron pots, crude potash is obtained, as a dark or 

 brown mass. This, when somewhat purified, yields 

 pearl-ash. Potassium carbonate, when pure, is white, and 

 has a bitter, biting taste the so-called alkaline taste. It 

 has such attraction for water, that, when exposed to the 

 air, it absorbs moisture and becomes a liquid. 



If hydrochloric acid be poured upon this carbonate a 

 brisk effervescence immediately takes place, owing to the 

 escape of carbon dioxide gas, and potassium chloride and 

 water are formed, which remain behind. 



K 2 CO 3 + 2 HCl = 2 KC1 -f H,O -f CO 2 . 



Potassium Bicarbonate, KHC0 3 . A solution of 

 potassium carbonate, when exposed to carbon dioxide, ab- 

 sorbs the latter, and the potassium bicarbonate is pro- 

 duced, so called because to a given amount of potassium 

 it contains twice as much carbonic acid as the carbonate. 

 Potash-salceratus consists essentially of this salt. It 

 probably exists in the juices of various plants. 



Sodium Carbonate, or Carbonate of Soda, 

 KaoCOs, 106. This substance, so important in the arts, 

 was formerly made from the ashes of certain marine 

 plants (Salsola and Salicornia), in a manner similar to 

 that now employed in wooded countries for the prepara- 

 tion of potash. It is at present almost wholly obtained 



