The Food of Plants 21 



the grains. Add moisture, and cork the bottles. Why are the 

 results different ? (Fig. 14.) 



9. Plant seeds in the same way in two cans of earth. Keep one 

 can swamped with water, and let the other can drain through 

 holes in the bottom so that the earth remains only moist. Explain 

 any difference in the growth of the seeds. 



10. Into a jar put a spoonful of soda, and pour a little vinegar 

 or other acid on it. The gas that is formed is carbon dioxid. It 

 will put out a match or a candle. To prove that the gas is heavy, 

 pour some of it from the jar into a*cup. A burning match put 

 into the cup will go out. 



11. Put a little gasoline or ether on the hand. Its rapid evapo- 

 ration cools the skin. The far more rapid evaporation of liquid 

 carbon dioxid would freeze the skin. 



