LIME. 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 lbs. of pure limestone 

 contains about 44 lbs. 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 w T ater 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 w r ay until it 

 has crumbled, it will effervesce again with muriatic 

 acid, as the limestone did before it was burned, thu,« 

 proving the fact just stated. 

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