CARBON DIOXIDE 117 



contains nitrogen compounds, hence ammonia is also 

 formed (cf. 112). 



The liquid that distils off from coal is called "coal tar." This is of 

 great commercial importance, for it contains benzene, aniline, etc., out 

 of which the wonderful coal tar dyes, as well as many other valuable 

 substances, are made (cf. 228) . 



The liquid obtained by the dry distillation of wood (Fig. 100) 

 contains wood alcohol, or "wood spirit," which is used to dissolve 

 certain gums, such as shellac, and as a fuel. Acetic acid is also formed 

 (cf. 123). 



125. Exercises. 



1. Do you think that the diamond would burn with a flame? 

 Why? 



2. What fuel does the blacksmith use for his fire? Why does he use 

 bellows? 



3. Does wood charcoal leave ash when burned? Does coke? Are 

 these pure carbon? Would sugar charcoal leave ash? 



4. Is it possible that coal is being formed now? Where? What 

 is "peat"? 



5. In what sense does coal contain the stored-up energy of the 

 sun? 



6. Turpentine burns with a smoky flame, while the flame of alcohol 

 is smokeless. What element is probably present in turpentine? How 

 can we prove that the same element is present in alcohol? 



7. Why does the wire gauze of the safety lamp prevent the flame 

 inside from setting the fire damp of the mine on fire? 



8. Why cannot gasoline -be burned safely in a lamp? Why cannot 

 kerosene be used in place of gasoline in the engine of an automobile? 



126. Carbon Dioxide. Carbon dioxide, or "carbonic 

 acid gas/' is formed when carbon and carbon compounds 

 ( c f- ^1 and 101) burn in air or oxygen. It is a colorless 

 gas that dissolves slightly in water, giving the water a 

 mildly acid taste. The solution is called carbonic acid. 



