38 AGRICULTURAL CHEMISTRY. 



ed up to the sun and air, and properly manured, to 

 become warm, healthy, and productive. 



55. Oxides of Manganese. — These, like the oxides of 

 iron, are numerous. Two — ^the protoxide (M.nO) and 

 the sesquioxide (Mn'^O^) — are constituted similarly to 

 the above oxides of iron. These are of little conse- 

 quence to agriculture, and will not be spoken of again 

 in this work. There is, however, another, which is of 

 some importance to agriculture. It is the peroxide^ 

 or, as more commonly called, the hlack oxide of man- 

 ganese (MnO^), containing, as its symbol imports, one 

 atom of manganese to two of oxygen. This exists in 

 great abundance at Bennington, Yt., and at many other 

 localities. It exists in small quantities in most rocks, 

 and is slightly diffused through nearly all soils. It is 

 found also in the ashes of most cultivated plants. 



56. Potash^ called by most writers potassa, (KO), is 

 not the common potash of the shops, used for soap- 

 boiling, but a far more bitter, acrid, caustic substance. 

 It is seen at the apothecaries in the form of small, 

 white rolls, not much larger than a pipe-stem, enclosed 

 in vials air-tight, to prevent its taking carbonic acid 

 from the air, and being turned to a carbonate of potash. 

 Its caustic (burning) power is very great, so that it 

 will readily dissolve horns, hoofs, bones, flesh, almost 

 any animal matter. In order to form a correct idea 

 of potash in all its changes, the learner must think 

 first of a white, shining metal, like silver, so soft that 

 you can cut it easily with a knife, and so light that it 

 will float on water, almost instantly taking fire, and 



