194 QUICK-LIME, CALCIUM, AND CHLORIDE OF CALCIUM. 



othei important offices, wliich we shall hereafter have occasion more 

 fully to consider. 



2°. Lime or Quick-lime. — When limestone is burned aloig with coal 

 or wood in kilns so constructed that a current of air can pass freely through 

 them, the carbonic acid is driven off, and the lime alone remains, in 

 this slate it is generally known by the name of burned or quick-Wme^ 

 from its caustic qualities, and is found to have lost nearly 44 per cent, of 

 its original weight. 



The most remarkable property of quick-lime is its strong tendency to 

 combine with water. This is displayed by the eagerness with which this 

 liquid is drunk in by the lime in the act of slaking, and by the great heat 

 which is at the same time developed. Slaked lime is a compound of 

 lime with water, and by chemists is called a hydrate of lime. It con- 

 tains 24 per cent, of its weight of water. 



The action of quick-lime upon the land is one of the most important 

 which presents itself to the observation of the practical agriculturist. 

 Among other effects produced by it is that of hastening the decomposi- 

 tion of vegetable matter either in the soil or in compost heaps ; but this 

 effect is materially promoted by — if it be not wholly dependent upon 

 — the presence of air and moisture. By this decomposition carbonic 

 acid and other compound substances are produced, which the roots are 

 capable of absorbing and converting into the food of plants. 



In this caustic state lime does not occur in nature, nor when exposed, 

 to the air does it long remain in this state. It gradually absorbs carbonic 

 acid from the atmosphere, and is again converted into carbonate. This 

 change takes place more or less rapidly in all cases where quick-lime is 

 applied to the land, but the benefits arisiug from burning the lime do not 

 disappear when it is thus reconverted into carbonate. On the contrary, 

 the state of very fine pov/der, into which quick-lime falls on slaking, 

 enables the carbonate of lime, subsequently formed, to be intermixed 

 with the soil in a much more minute state of division than could be ob- 

 tained by any mechanical means. This we shall hereafter see to be a 

 most important fact, when we come to study in more detail the theory 

 of the action of lime in the several states of combination, and under the 

 varied conditions in which it is employed for the purpose of improving 

 the land. 



3°. Calcium is a silver-white metal, which, by its union with oxygen, 

 forms lime. It is not known to exist in nature in an uncombined state, 

 is prepared artificially only with great difficulty, and therefore exercises 

 no direct action on vegetable growth. 



4°. Chloride of Calcium. — When chalk or quick-lime is dissolved in 

 muriatic acid, a solution of chloride of calcium is obtained. This solu- 

 tion occurs in sea-water, in the refuse (mother-liquor) of the salt-pans, 

 and is allowed to flow away in large quantities as a waste from certain 

 chemical works. I have elsewhere stated the effects it has been ob- 

 served to produce upon vegetable growth, [see Appendix,] and have re- 

 commended the propriety of making experiments with the view of ren- 

 dering useful some of those materials which in our manufactories are 

 now suffered largely to run to waste. 



5°. Sulphuret of Calcium is a compound of sulphur and calcium, 

 which may be formed by heating together chalk and sulphur in a covered 



