VfiOETABLE MANURES. ] 55 



24 1 . Use of lime as manure, — When common limestone 

 {carbonate of lime) is buraed in the kiln, the carbonic aciil, 

 which forms so large a portion of its bulk (45), is expelled 

 into the air, and it becomes a porous mass, and experiences 

 an important alteration in its properties. As it exists in the 

 mountains, it is, as you are aware, both tasteless and insolu- 

 ble; but, by burning, it acquires a caustic taste, and is 

 rendered slightly soluble in water. In the bu?med state, lime 

 has, from a very early period, been employed as an applica- 

 tion to the soil in every part of Europe, and in many parts of 

 this country is consumed at the present time in enormous 

 quantities. As the effects which lime is capable of producing; 

 upon the soil, are in general very little understood by the 

 greater number of our farmers, it will be necessary for us 

 carefully to consider the nature of its operation, and also 

 the composition of the rocks from which it is procured. 



242. When water is thrown upon burned or quick lime, it 

 rapidly absorbs it, gives out so much heat as to char wood, 

 aud falls into pieces. When exposed to the air, it also 

 attracts moisture, and crumbles to powder; in this state it is 

 termed slaked, or slacked lime, and is found to have increased 

 considerably in weight, a ton of quicklime being converted into 

 about 25 cwt. of slaked lime. It also gradually attracts car- 

 bonic acid from the air, and returns to the state of carbonate, 

 though even after a very long period portions of it remain 

 caustic. In this state it is usually termed mild Ume, though, 

 when allowed to slake in the fields, only about one-half of 

 it is found to have entered into combination with carbonic 

 acid.* 



nitric acid. It is formed in compost heaps during the decay of organic 

 matters containing nitrogen, and produced in the atmosphere during 

 thunder-storms. It is believed by many persons that its compomids 

 exercise a powerful effect on the growth of plants, by supplying 

 nitrogen. 



• The teacher may allow his pupils to perform the following simple 

 «3q)eriments : — 



1. Let 25 grains of common unbumed lime be weighed, and intro- 

 duced into a glass containing about two teaj^poonfuls of muriatic acid 

 (spirits of salts), diluted witli an equal quantity of water ; a copious 

 effervescence will be produced, and it will nearly all dissolve : test the 

 gas which escapes, as directed at page 30. When the effervescence has 

 ceased, pour off the lic^uid without disturbing the undissolved matter, 

 which may be washed so as to remove all trace of tlie acid, by pouring 

 water upon it and decanting; the sediment collected on a piece of blotting- 



n2 



