10 AGRONOMY 



Silicon (Si) when pure consists of lustrous brown or black 

 crystals, but it does not exist in nature uncombincd. Xext to 

 oxygen it is the most widely distributed of the elements and 

 forms one fourth of the earth's crust. In combination with 

 oxygen, silicon forms the clear and glasslike mineral quartz 

 (SiO 2 ), and is thus the principal element in sand. From 60 

 to 90 per cent of most soils is quartz. 



PRACTICAL EXERCISES 



1. Look over the list of chemical elements given on page 3 and 

 name those possessed by the class in the shape of jewelry, coins, etc. 



2. Make a list of these and of the others that may be found in the 

 schoolroom. 



3. Visit the chemistry department of the school, or the nearest drug 

 store, and list any other uncombined elements that you may find. 



4. In the laboratory, by appropriate experiments, make carbon diox- 

 ide, sulphur dioxide, magnesium oxide, etc. 



5. Pick out the chemical elements in the following combinations : 

 orthoclase(KAlSi 3 O 8 ),carnallite(KClMgCl 2 6H 2 O), common salt(XaCl), 

 Epsom salts (MgSO 4 ), copperas (FeSO 4 ), nitric acid (HXO 3 ). 



6. Burn a piece of limestone to drive off the CO 2 , leaving quicklime 

 (CaO). Add water to a piece of quicklime to make calcium hydroxide 

 and note the heat developed by the chemical reaction. 



7. Boil some water in a Florence flask and watch the space above the 

 boiling water. What is the color of the gas (steam)? 



8. Watch the bubbles of gas rising from any water plant when in 

 sunlight. Catch some of it by sinking a short-stemmed glass funnel 

 into the water over the plants, with the stem just below the surface, 

 and inverting over it a test tube filled with water. The gas will rise 

 and displace the water in the tube and may be tested with a glowing 

 splinter. 



References 



Hopkins, " Soil Fertility and Permanent Agriculture." 

 Snyder. "Chemistry of Plant and Animal Life." 



