LIME. 291 



forms a hydrate. The hydrate, like that of potassa, is 

 dry, although it contains a large portion of combined 

 water. As the water thus becomes solid in the com- 

 pound, its latent heat is given off to the air or sur- 

 rounding objects. The employment of heat thus pro- 

 duced for culinary operations has been recently sug- 

 gested. If the process of slaking be conducted 

 under a tumbler, with a slight surplus of water, steam 

 will be produced. On lifting the tumbler, it will be- 

 come visible by its condensation into vapor. 



728. IGNITION BY LIME. The heat 



How may gun- 



powder be iff- thus produced, is often sufficient to ignite 

 Ik^en^of gun-powder. It should be sprinkled on 

 lime? the mass, and kept dry while the slaking 



proceeds. Warm water and well-burned lime should 

 be employed in the experiment. 



729. ACTION OF THE AIR. If lime is 



What is the 



action of the exposed to the action of the air, it gradu- 



aironlime? cart)On i c acid and 



water, and becomes converted into a mixture of hydrate 

 and carbonate. It is then called air-slaked lime. By 

 sufficiently long exposure the conversion into carbo- 

 nate is complete. 



730. LIME IN MORTAR. Ordinary mortar 

 mortar har- is a mixture of sand and lime. It hardens 

 not simply by drying, but by the absorp- 

 tion of carbonic acid from the air. A compound of 

 hydrate and carbonate of lime, possessed of great hard- 

 ness, is thus produced. A gradual combination, also 

 takes place between the silica and the lime, which 

 binds the two constituents still more firmly together. 



