MANURES. 45 



|iii|><>-'\ by nuidriiMiig ammonia nitric acid and the 

 of the atmosphere. 



CHARCOAL, 



Scattered over the ground, produces the same effect as the 



::oing, and probably in a greater degree ; as it absorbs 



and condenses the nutritive gases within its pores, to the 



amount of from 20 to over 80 times its own bulk. The eco- 



nomy and benefit of such applications can be readily under- 



stood, as they are continually gleaning these floating materi- 



iioiu the air, and storing them up as food for plants. 



Charcoal as well as lime, often checks rust in wheat, and 



mildew in other crops ; and in all cases mitigates their rava- 



ges, where it does not wholly prevent them. 



BROKEN GLASS 



Is a silicate of potash or soda, according as either of these 

 alkalies are used, in its manufactures. Silicate of potash, 

 (silex and potash chemically united,) is that material in 

 plants, which constitutes the flinty, outer coating of the 

 grasses, straw, cornstalks, &c. ; and it is found in varying 

 quantity in all plants. It is most abundant in the cane, 

 Indian corn, the stings of nettles, and the prickly spikes in 

 burs and thistles. Some species of the marsh-grasses have 

 these silicates so finely yet firmly adjusted, like saw-teeth on 

 their sharp edges, as to cut the flesh to the bone when drawn 

 across the finger. Every farmer's boy has experienced a yet 

 more formidable weapon in the exterior of a cornstalk. 



It is to the absence of this material in peat and such other 

 soils as have an undue proportion of animal or vegetable ma- 

 nures, that we may attribute the imperfect maturity of the 

 grain and cultivated grasses grown upon them, causing them 

 to crinkle and fall from the want of adequate support to the 

 stem ; and it is to their presence in excess in sandy and cal- 

 careous soils, that the straw is always firm and upright, 

 whatever may be the weight of the bending ear at the top. 

 By a deficiency of silicates, we mean, that they do not exist 

 in a soluble form, which is the only state in which plants can 

 seize upon and appropriate them. The efforts of the roots in 

 procuring this indispensable food are so irresistible, that they 

 have been known to decompose glass vessels in which they 

 have been grown. Before using, the glass should be redu- 

 ced to powder by grinding. 



