LECTURE XVII. 



Use of lime as a manure. — Value of lime in improving the 8oil. — Of the composition of 

 common and magnesian lime-stones. — Burning and slaking of lime. — Changes which 

 slaked lime undergoes by exposure to the air. — Various natural states in which carbonate 

 of lime is applied to the land. — Marl — shell and coral sand,— limestone sand and gravel, 

 — crushed lime-stone. — Chemical composition of various marls, and shell and lime-slone 

 Bands. — Their effects on the soil. — Use of chalk. — Is lime necessary to the soil? — Ex- 

 hausting effect of lime Analogy between this action of lime and that of wood-ashes. 



Quantity of lime to be applied. — Effects of an overdose. — Form in which it may be most 

 prudently used. — When it ought to be applied in reference to the season — to the rotation 

 — and to the application of manure.— Its general and special effects on different soils and 

 cropa. — Circumstances which influence its action. — Length of time during w hie it its ef- 

 fects are perceptible. — Theory of the action of lime. — Necessity and nature of the ex- 

 haustion which it sometimes produces. — Sinking of lime into the soil. — Why the a()pli- 

 cation of lime must be repeated. — Action of lime on living animals and vegetables. 

 Suggestions of theory. — Use of silicate of lime. 



Having explained to you the action of the most important saline 

 and mixed mineral substances which are or may be beneficially ap- 

 plied to the soil, I have now to draw your attention to the use of lime 

 ■—the most valuable and the most extensively used of all the mineral 

 substances that have ever been made available in practical agricul- 

 ture. It has, and with much reason, been called " the basis of all 

 good husbandry" — it well deserves, therefore, your most serious atten- 

 tion as practical men, and on my part the application of every chem- 

 ical light by which its usefulness may be explained and your practice 

 guided. This consideration also will justify me in dwelling upon it 

 with some detail, and in illustrating separately the various points, 

 both of theory and practice, which present themselves to us, when 

 we study the history of its almost universal application to the soil. 



§ 1. O/* the composition of common and magnesian lime-stones. 



1°. Common limestones. — Lime is never met with in nature except 

 in a state of chemical combination (Lee. I., § 5,) with some other 

 substance. That which is usually employed in agriculture is met 

 with in the state of carbonate. 



Carbonate of lime, or common lime-stone, consists of lime and car- 

 bonic acid, and when perfectly pure and dry, in the following propor- 

 tions : — 



per cent. 



Carbonic acid 43-7 ^ 



Lime 56-3 ( or one ton of pure dry carbonate of 



I lime contains Hi cwts, of lime. 



100 J 



Limestones, however, are seldom pure. They always contain a sen- 

 sible quantity of other earthy matter, chiefly silica, alumina, and oxide 

 of iron, with a trace of phosphate of lime, sometimes of potash and soda, 

 and often of animal and other organic matter. In lime-stones of the 

 best quality the foreign earthy matter or impurity does not exceed 5 per 

 cent, of the whole — while it is often very much less. The chalks and 



