180 Chemistry. [Lecture 30- 



water sets free a quantity of caloric, and heat is 

 produced. Since heat or fire then diminishes the 

 weight of lime, a knowledge of this fact must be 

 of great use to farmers, for by burning the lime- 

 stone on the spot where it is found, they have 

 much less expense of carting. A red heat is 

 necessary to burn lime. When the mass of lime 

 is saturated with water, every particle of the calx 

 is united to a proper quantity of the fluid ; and 

 it is now called calx extincta, or slacked lime, 

 which has not the same attraction for water as 

 quick-lime, but agrees with it in every other 

 quality. Slacked lime, though it appears dry, 

 contains a great deal of water. The water ad- 

 heres closely to it ; but by red heat it may again 

 be separated, and the lime becomes again quick. 



The attraction which lime has for water is the 

 principal reason of its use in building ; for while 

 in a soft state it adheres to the stones or bricks 

 as a cement, and speedily becomes solid. The 

 solidity is increased by attracting carbonic acid 

 from the atmosphere, so that if mortar is well made, 

 the older it is the stronger cement it becomes. 



It is not only in the state of a carbonat that 

 lime is found in nature. It is often united with 

 sulphuric acid; in this state it is, as before in- 

 timated, scientifically called sulphat of lime, and 

 vulgarly gypsum. 



Gypsums are found in stony masses, very soft, 

 and easily scraped with a knife. They are di- 

 stinguished from chalks and limestones by not 



