SUMMARY 



123 



Carbon Dioxide 

 1 ~ 



Lime- 

 stone 



When limestone is heated to a high temperature, it is 

 decomposed, giving lime and carbon dioxide. The appara- 

 tus is called a lime kiln (Fig. 108). Lime 

 is used to make mortar and plaster. It 

 is first "slaked" with water, and the 

 "milk of lime" that is formed is mixed 

 with sand. When the mortar "sets," it 

 takes up carbon dioxide from the air, 

 forming limestone once more. This 

 fastens bricks and stones firmly together, 

 and we call it mortar. When it forms a 

 stony covering for our walls we call it 

 plaster. 



Lime 



FIQ. 108. 

 A Lime Kiln. 



133. Summary. Carbon exists as diamond, graphite, coal, coke, 

 charcoal, soot, etc.; also as one of the elements of sugars, starches, 

 fats, proteids, and of living creatures. When heated, most substances 

 containing carbon are charred. 



Coal was probably formed out of vegetation. 



Uses of carbon are: for filters, black paints, printer's ink, pencils, 

 fuel, etc. Diamonds are used as jewels and as cutting materials. 

 Carbon is the element used to reduce the ores of the metals. 



Hydrocarbons are compounds of carbon and hydrogen. 



Petroleum is a mixture of hydrocarbons found in the earth. Dis- 

 tillation of petroleum gives gasoline, kerosene, vaseline, paraffin, etc. 



The flashing point is the temperature at which a mixture of the 

 vapor of kerosene and air can be set on fire. 



Dry distillation of soft coal gives illuminating gas, ammonia, coal 

 tar, coke, etc. Dry distillation of wood gives wood spirit, acetic acid, 

 charcoal, etc. 



Carbon dioxide is formed by the burning of carbon and its com- 

 pounds, by the breathing of animals, by the action of acids upon car- 

 bonates, by fermentation, by the action of baking powders, and by the 

 heating of limestone. 



