124 CARBON AND ITS COMPOUNDS 



It is a colorless gas, heavier than air, somewhat soluble; it neither 

 burns nor permits other things to burn. Carbon dioxide is used to 

 raise dough, as a fire extinguisher, and as the material needed to harden 

 plaster and mortar. By its presence in water it causes limestone to 

 dissolve. It serves as a food for plants. 



Limestone is calcium carbonate', so are marble, coral, etc. When 

 limestone is heated very hot, lime remains. Lime and water combine 

 to give " slaked lime," or calcium hydroxide. Lime water is a solution 

 of calcium hydroxide. 



134. Exercises. 



1 . What is the danger of sleeping in a room containing a stove? 



2. When soda is put with tomatoes, effervescence takes place. 

 What gas is being formed, and why? 



3. How could you remove the limestone of a bone, so that you 

 could tie the organic matter, which remains, in a knot? How could 

 you destroy the organic matter, and leave the mineral matter? 



4. Would a carbon dioxide fire extinguisher be better for fires near 

 the floor or near the ceiling? 



5. If a candle is put into an old well, and "goes out," what gas is 

 probably present? Is it safe for a man to enter such a w r ell? 



6. Mines are sometimes filled with "fire damp," and sometimes 

 with "choke damp." What gas is "choke damp?" 



7. Open stoves "salamanders" containing burning charcoal 

 are often placed in freshly plastered buildings. How do they help 

 to harden plaster? 



8. Where do clams, oysters, snails, etc., get the limestone out of 

 which they build their shells? Where does the limestone of our 

 bones come from? 



