AGRICULTURAL CHEMISTRY. 39 



burning brilliantly as it touches cold water or ice even. 

 This is potassium (K). Now, if 8 parts, by weight, of 

 oxygen be combined with 39 parts of this metallic po- 

 tassium, we have caustic potash (KO), the intensely 

 bitter, burning substance of which I have been speak- 

 ing. If, then, 37 parts, by weight, of this caustic 

 potash (KO) be combined with 22 of carbonic acid 

 (CO'), we shall have the common carbonate of potash 

 of commerce (KO, CO'). As found at stores, it is 

 generally very impure. If now we take the dingy, 

 gray potash of commerce, purify it of its foreign mix- 

 tures, and treat it to another dose of carbonic acid, 

 we shall have saleratus, hicarhonate of potash (KO, 

 2C0'). Besides various other forms, we have then these 

 four, in which potassium is exceedingly useful in the 

 sciences, arts, and common affairs of life — viz., metallic 

 potassium (K), caustic potash (KO), carbonate of potash 

 (KO, CO'), and bicarbonate (KO, 2C0'). In the form 

 of ' common carbonate of potash only is it used 

 for agricultural purposes. It is in this form that it 

 exists in ashes. Ordinary wood ashes contain about 

 6 per cent, of carbonate of potash, some 2 per cent, 

 of carbonate of soda, and about 75 per cent, of car- 

 bonate of lime. It is manifest, therefore, that farmers, 

 who sell their ashes at the price generally paid by 

 soap-boilers, and those who do not buy at these prices 

 when they have an opportunity, commit a " mistake." 



57. Soda (NaO). — This is caustic soda, consisting 

 of sodium (Na), and oxygen (0). In this form it is 

 useful in the arts and sciences, but is seldom seen or 

 known in domestic concerns. Similar remarks apply 



