SCIENCE OF COMMON THINGS. 



Ceenta. Quicklime. Whitewash. 



CHAPTEE III. 



APPLICATION OF MATERIALS FOB ARCHITECTURAL OR 

 STRUCTURAL PURPOSES. 



210 What are cements? 



Cements are for the most part soft or semi-fluid sub- 

 stances which have the property of becoming hard in 

 time, and cohering with other bodies to which they have 

 been applied. 



22O Of what are the ordinary cements which are called mortars com- 

 posed f 



Of quicklime, sand, and water. 



{321 What is quicklime? 



Quicklime is principally pure lime, and is obtained, 

 from the limestone rock, ordinary marble, or shellr, 

 which are composed of carbonate of lime, by calcina 

 tion. The effect of the burning is to drive on the car- 

 bonic acid, leaving the lime pure and uncombined. 



J3SS What is slacked lime f 



If quicklime obtained as above described be wet 

 with water, it instantly swells and cracks, becomes 

 exceedingly hot, and at length falls into a white, soft, 

 impalpable powder. This is denominated "slacked 

 lime. 



223 What is ordinary whitewash f 



A mixture of slacked lime with water. 



224 Why should slacked lime intended for mortars be excluded from 

 the air, or used soon after it has been prepared f 



Because if exposed to the air it absorbs carbonic 

 acid, and becomes converted again into its former con- 

 dition of carbonate of lime. 



225 Why does mortar become hard after a few days f 



A portion of the water evaporates, and the lime by 

 a sort of crystallization adheres to the particles of sand 



