4:0 SCIENCE OF COMMON THINGS. 



Brides with straw. Tiles] Mastic. 



by the heat into the red oxide of iron, and acts in this 

 state as red coloring material. 



334 Why are the bricks manufactured at Chicago, and some other 

 parts of the Western country, of a white or yettow color f 



Because the clay of which they are formed does not 

 contain sufficient iron to color them. 



335 Why did the children of Israel in making bricks desire to mix 

 straw with the clay f 



j, The bricks of the Egyptians were composed of clay 

 simply baked in the sun, and not burnt. By using 

 straw the clay was held together more firmly and the 

 brick rendered stronger. 



336 Why are the Egyptians enabled to dispense with the process of 

 burning the bricks ? 



The extreme dryness of the climate in which they 

 were used enable them to dispense with the burning. 

 Bricks from Egypt and Babylon, which have remained 

 exposed to the open air uninjured for two thousand 

 years, rapidly fall to pieces when transported to a 

 moist climate. 



237 Why do we mix hair with mortar f 



In order to render it more cohesive and stronger. 



338 What are tiles f 



Plates of burnt clay resembling bricks in composi- 

 tion and manufacture, and used for the coverings of 

 roofs or floors. 



339 What is mastich or mastic t 



The name given to those cements which contain ani- 

 mal or vegetable substances in composition. Mastich 

 used for the external decoration of houses often con- 

 tains oil and a preparation of lead. 



340 What is putty? 



Putty, used by glaziers in setting window-glass and 

 for other purposes, is composed of whiting and linseed- 

 oil, mixed and worked together. "Whiting is simply 

 common chalk ground and purified. 



