120 PLANT FOODS AND PLANT GROWTH 



forced out by the gas. When all the water has been forcod out, cover the 

 mouth of tlie bottle with a card and invert. Repeat until three or four 

 bottles are filled. 



This gas is oxygen. Note its color. Thrust glowing pieces of char- 

 coal into the bottles and note the result. Explain. 



11. Study of Carbon Dioxide. — Put some small fragments of marble 

 into a flask thoroughly closed with a cork through which has been passed 

 a delivery tube as in; Exercise 10, and a small funnel or thistle tube. Pour 

 dilute hydrochloric acid into the funnel until the lower end is covered. 

 Collect the resulting gas (carlwn dioxide) as in Exercise 10. Run a 

 little of the gas into lime water and note the result. Take a little fresh 

 lime water and blow into it through a straw or tube. Note the result. 

 Explain. 



12. Burn a piece of charcoal in a l)ottle of pure oxygen. Remove 

 quickly, pour in lime water and shake. Note the result. Explain. 



13. Study of Hydrogen. — Put a few fragments of zinc into the 

 same or a similar apparatus as used in Exercise 10. Add the dilute 

 hydrochloric acid but allow the gas to be given ofl' for some minutes. Then 

 collect a bottle of the gas (hydrogen) and place upside down on a table. 

 Darken the room and thrust a burning match into the inverted bottle. 

 Note the result. 



14. Study of Nitrogen. — Fasten a bit of candle to a cork and float 

 in a vessel of lime water. Light the candle and cover with a wide bottle 

 so placed that the edges are under water. When the candle goes out, 

 cover the mouth of the bottle with card-board or cork and reverse so as to 

 retain all the water that has risen in tlie l)ottle. Shake thoroughly, and 

 allow to stand until the upper part is clear. What has been used by the 

 burning candle? What gas has Ijeen formed as indicated by the lime water 

 in the bottle? The gas remaining in the bottle is nitrogen. 



QUESTIONS 

 L What are the three great groups of substances found in plants? 



2. Of what elements are each of these food substances composed? 



3. What are the sources of these elements? 



4. What otlier elements are found in plants? 



5. What relation does the texture of the soil bear to the water con- 



tent? 



6. What do you understand by humus? 



7. What do you understand by turgor? 



8. What do you understand by osmosis? 



9. Why do plants wilt? 



10. What do you understand by transpiration? 



11. What do you understand by piiotosynthesis? 



