Lime, Its Value and Importance 1673 



The term " lime " is applied loosely to several products — 

 calcium oxide, or burned or lump lime; calcium hydrate, or water- 

 slaked lime; calcium carbonate, or ground limestone or marl; cal- 

 cium sulphate, or gypsum or land ]ilaster. 



In the beginning of this discussion it is necessary to eliminate 

 gypsum, since it does not have the power to correct acidity — a 

 condition which lime, in general, is used to overcome — even 

 though it may perform some of the other functions of lime. Also, 

 it is almost universally held at a price which makes its use 

 prohibitive. 



Calcium carbonate is the natural source of all lime compounds 

 used in soil improvement, and occur^^ in nature in great abundance 

 in the fomi of limestone, shells and marl. If it is decided to use 

 limestone, that which contains at least 90 j^er cent, of calcium 

 carbonate should be insisted u]ion. 



Quick or burned lime is the most concentrated of the common 

 lime materials. It is produced generally by burning in a kiln a 

 carbonate of lime, such as limestone. By this method the car- 

 bonate is divided into two compounds, carbon dioxide and quick- 

 lime. The carbon dioxide is driven off as a gas and makes up 

 44 per cent, of the carbonate of lime with which the operation 

 began. In other words, in each hundred pounds of carbonate of 

 lime, assuming it to be pure, there are 56 pounds of burned lime. 

 Stated another way, nearly two tons of limestone must be employed 

 to make one ton of burned lime. 



When burned lime and water enter into combination hydrated 

 or water-slaked lime is produced. Commercially prepared it 

 occurs as a fine, white, dry powder, and is easy to apply to the 

 soil. In the process of slaking, 56 pounds of fresh burned lime are 

 increased to 74 pounds of hydrated lime by the addition of 18 

 pounds of water. Or, a ton of hydrated lime contains 486 pounds 

 of water and 1,514 pounds of actual lime. 



Many of the hydrated limes on the market contain considerable 

 quantities of carbonate of lime, and aside from their physical 

 condition are but little better than ground limestone. Generally 

 hydrated limes are held at prices much higher than their actual 

 value would warrant. 



