The Problem of Impoverished Lands. 119 



They come from the ground. They are sohds. 



9. Where does oxygen come from f 



It comes from the air ; about one-fifth of the air is oxygen and 

 four-fiftlis nitrogen. 



10. Do you know if phosjyhorus, potassium and calcium exist 

 in nature in their pure state f 



In nature they exist only as compounds with other substances. 



11. Does oxygen exist anywhere in a pure or uncombined state? 

 Yes ; oxygen exists in the free or uncombined state in tlie atmo- 

 sphere. About one-fiftli of the atmosphere is oxygen. 



12. Of what is water composed f Write its che?nical formula. 

 Of liydrogen and oxygen ; the symbol or formula is HgO. 



IS. Of ivhat is ammonia composed f Is it a gas or liquid f 

 Can you htiy ^ntre ammonia at the drug store ? 



It is composed of nitrogen and hydrogen (N Hg). It is a gas. 

 Ammonia of the drug stores is water which has absorbed some of 

 the ammonia gas. 



14. Does the p>lant feed on ammonia directly f 



Very little, if at all. It must first be changed to a nitrate. 



15. What is the composition of a nitrate? Write the formula 

 for nitrate of potash and nitrate of lime. 



Nitrates are the result of treating substances with nitric acid. 

 For nitrate of potash it is K NO3 ; for nitrate of lime, Ca (N03)2. 



16. In what kind of materials does nitrogen occur ? Name 

 some common things lohich you think contain nitrogen. 



Nitrogen occurs in organic materials, as in plants and animals. 

 In meat, leather, hair, milk, humus of the soil, cotton-seed meal, etc. 



17. Is nitrogen a solid or a gas ? 

 It is a gas. 



18. Are nitrates of potash and soda solids, liquids or gases ? 

 They are solids. 



19. Are nitrates soluble ? Is there danger of their being lost 

 from the soil ? 



Yes. Loss is likely to occur, especially on land which remains 

 for a long time with no crop on it. ' 



20. What is an amendment ? 



A substance which, while it has little or no value as a plant-food 



