LJME. 109 



OF SALINE AND MINERAL MANURES. 



The last class of manures embraces those of a saline 

 and mineral character. These are numerous, but not 

 many of them have been as yet largely used in this 

 country. Beside those which are known here, I shall 

 mention a few of those that have been found most 

 efficacious abroad. 



SECTION IV. OF LIME. 



I will commence with a mineral manure, whose use 

 is most widely extended, in every country where agri 

 culture has made much advance. I refer to lime. 



Lime is ordinarily found in the form of common 

 limestone, or carbonate of lime, a combination of lime 

 with carbonic acid. Every 100 Ibs. of pure limestone 

 contains about 44 Ibs. of carbonic acid gas. This 

 may be driven off by a high heat, as in the lime-kilns. 

 The lime then remains in what is called the caustic 

 state, or quicklime. It will burn the tongue, if ap 

 plied to it. When water is poured upon it (this may 

 be shown by teachers), it swells, cracks, heats, and 

 finally crumbles to a fine powder. If the water is 

 only used in sufficient quantity to slake the lime, it 

 will all disappear, being entirely absorbed: it has in 

 fact united with the lime, and become a part of the 

 solid stone. The heat during slaking is caused by the 

 chemical union of water and lime. A ton of lime 

 stone unites with about one-fourth of a ton of water. 



If quicklime or slaked lime is exposed to the air, it 

 gradually absorbs carbonic acid; and if left a long 

 time, becomes nearly all carbonate once more. If a 

 piece of quicklime be left exposed in this way until it 

 has crumbled, it will effervesce again with muriatic 

 acid, as the limestone did before it was burned, thus 

 proving the fact just stated. 



