THE NATURE AND NEEDS OF LIVING MATTER 21 



Method b. Heat some sugar and some starch in separate 

 test tubes. What results ? 



Conclusions. 1. Do they contain carbon ? Reasons? 



2. What do you think is 

 indicated when certain foods 

 are scorched ? 



3. Name some foods that 

 you think must contain 

 carbon. 



4. How, do you infer, 

 does the human body ob- 

 tain a supply of carbon ? 



Method c. Burn a bit of 

 charcoal (carbon) in the 



wide-mouth bottle, then add 



P -, /. i . FIG. 5. Separating wood into gas and 



two spoonfuls of hmewater charcoal (c P arbon) g p> clay pipe 8 contain . 



and shake the bottle. ing bits of shavings and covered with 



Observations. 1. Is the wet clay; I, flame made by lighting the 

 carbon entirely consumed ? gas as [t issues from the stem ' 



2. Is there any change in the limewater ? 



Note. It is known that nothing but carbon dioxide will 

 cause limewater to become milky. Carbon dioxide is formed 

 by a chemical union of carbon with oxygen. It is really an 

 oxide of carbon. (See Prob. I, &, for further notes.) 



Conclusions. 1. How is carbon dioxide formed? 



2. What is the test for the presence of carbon dioxide ? 



Method d. Breathe through a tube into some limewater. 

 Result ? 



Conclusions. 1. What do you decide must be one of the 

 substances that comes from the lungs ? Reasons ? 



2. How must this substance have been formed ? 



3. What must be one of the elements in the human body ? 



Questions 



1. Can you think of any advantage in the presence of 

 nitrogen in the air? 



