The Soil and its Treatment. 15 



Calcium Carbonate. Quick-lime is obtained by " burning " 

 or heating to redness any form of carbonate of lime (calcium 

 carbonate). Limestone rock, chalk, marble, seashells, &c., are 

 all natural forms of carbonate of lime. The lime which forms 

 part of these materials is combined with carbonic acid; 

 under the influence of great heat the carbonic acid is driven 

 oft and only the quick-lime remains. As everyone who has 

 any practical acquaintance with quick-lime is aware, it is 

 only kept " quick " with difficulty ; if it is exposed to a damp 

 atmosphere it rapidly becomes " air-slaked " and falls to a fine 

 powder. 



When quick-lime is applied to the soil it first absorbs water 

 and becomes " slaked "; it then gradually unites with carbon 

 di-oxide, and returns to its original form of calcium carbonate. 

 Until this last change takes place the lime remains caustic and 

 when in this condition is frequently injurious to the roots 

 of plants. Therefore unless for special reasons, such as 

 when a soil is infested with disease, in which case quick-lime 

 is best it is better and generally cheaper to apply lime in the 

 form of ground limestone or chalk. 



Lime in any form should not be buried deeply, as it has a 

 tendency both to sink further into the ground and to be dis- 

 solved out of the soil by the carbonic acid in rainwater. 



Gas-lime or " blue-billy " is an evil-smelling substance pro- 

 duced by the use of lime in purifying coal-gas. In its fresh 

 state it contains calcium sulphide and sulphite and it is then 

 deadly to both plant and insect life. It is sometimes applied 

 fresh to ground badly infested with some insect pest, in which 

 case five tons to the acre should be evenly spread and imme- 

 diately turned under, but the ground cannot then be cropped 

 for several months after. By exposure to the air the poisonous 

 substances are changed into sulphate of lime and it can then 

 be used with perfect safety. To accomplish this change in the 

 best way lay the crude material in heaps of about a ton, and 

 after a month or so mix each heap with an equal quantity of 

 soil, such as ditch cleanings and the like. Let it stand in these 

 heaps for about a year and then apply the mixture at the rate 

 of four tons per acre. 



