LIME 49 



given to the limestone denotes precisely this combina- 

 tion. As it is when taken from the ground, the stone 

 contains the two substances closely united, so incor- 

 porated indeed as no longer to have the qualities 

 characterizing them when apart. Heat destroys this 

 union: the lime stays in the kiln, and the carbonic 

 acid gas is dissipated in the atmosphere with the 

 smoke from the burnt fuel. After this liberation of 

 the gas the lime is left in its pure state, no longer 

 masked by the presence of another substance, but just 

 as it is needed by the mason for making mortar." 



"Then all that the fire does," queried Jules, "is 

 just to break apart the limestone and drive out the 

 carbonic acid gas that it contained!" 



"What takes place in the lime-kiln," replied his 

 uncle, "is nothing but the separation of the lime 

 and the gas. Now let us turn our attention to the 

 mortar. When lime is watered, it gets very hot, 

 swells, cracks open, and crumbles into a fine powder 

 like flour. The heat that is generated comes from 

 the violence with which the two substances rush to- 

 gether. Before absorbing water lime is called quick- 

 lime ; after this absorption, which has reduced it to 

 powder, it is called slaked lime. This slaked lime is 

 reduced to a paste with water, and then well mixed 

 and kneaded with sand. The result is the mortar 

 used in laying stone and brick in order to hold the 

 courses firmly together and give solidity to the 

 building. 



"There is one thing I advise you to note, if you 

 have not already done so, since it will explain to you 



