AGRICULTURAL TEXT-BOOK. 325 



potash, soda, and sulphuric acid, (the carbonic acid being a pro 

 duct of combustion, and of no intrinsic value) ; and when ashes 

 are thus separated on a large scale, a notable quantity of the 

 alkalies remains behind. Though the refuse is not immediately 

 soluble, it will become available to plants in the soil by chemical 

 action, and the power which roots appear to possess of decom 

 posing mineral matter; while such alkalies as remain will act on 

 the silica, and form soluble silicates for grass and the stalks of 

 grain. 



In leaching, more or less lime is always added for the pur 

 pose of depriving the potash of its carbon, and rendering it 

 caustic, so that the common leached ashes are richer in lime than 

 before the process commences. According to Dana, a bushel of 

 good ashes contains about 5^- pounds of real potash. In leach 

 ing ashes, generally about one peck of lime is added to each 

 bushel of ashes, and as it loses no bulk during the operation, a 

 cord of leached ashes contains about the following proportions 

 allowing an average of 4 Ibs. per bushel to be leached 



out: 



Ibs. 



Phosphoric acid, - - 117 



Silex, - 146 



Oxide of iron, 17 



Oxide of manganese, - - 51 



Magnesia, - - - - 119 



Carbonate of lime, including that added in leaching, - 3072 



Potash combined with silica, - - 50 



Spent ashes therefore belong to the class of carbonates ; and 

 to the farmer are worth very nearly as much as the unleached. 



In nearly the whole range of soils, ashes are beneficial to 

 cultivated plants; but much more so on sandy and gravelly 

 lands than on clay, which being chiefly formed of granite 

 rocks naturally contain potash. We have also seen, in the 

 analyses of plants, that certain genera, such as turnips, carrots, 

 potatoes, beets, &amp;lt;kc., contain a very large amount of the alka- 



