Lime 



furnace, and how it turns into lime by 

 passing through the fire. Chalk contains two 

 different substances : lime in the first place, 

 and also a gas, carbonic acid gas, which is as 

 invisible and impalpable as air itself. The 

 name carbonate of lime, which is given to 

 chalk, denotes this combination exactly. As 

 it is extracted from the ground the chalk 

 holds the two components in close associa- 

 tion, forming one substance, and not pos- 

 sessing the properties which they have when 

 separated. Heat destroys this association and 

 the lime remains in the kiln, while the carbonic 

 acid gas is dispersed in the atmosphere 

 with the smoke of the fuel. Having lost the 

 gas, the lime, the properties of which are no 

 longer concealed by the presence of another 

 matter, remains as it is needed by the mason 

 for his mortar. 



So the action of the fire consists in decom- 

 posing the chalk and expelling the carbonic 

 acid gas which is associated with it ; and the 

 process in the kiln is only the separation of 

 the gas and the lime. We will now consider 

 the mortar. When it is sprinkled with water 

 the lime becomes very hot, cracks and falls 

 into fine dust like flour. The heat evolved 

 arises from the violence with which the two 



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