298 GENERAL SCIENCE 



a crop is grown. A crop is usually grown every other 

 year ; but sometimes two crops are grown in three years. 



Experiment 76. To determine the per cent of water, organic 

 matter, and mineral matter in soils. Weigh a crucible. Place ten 

 grams of the soil to be tested in it. Heat to a temperature of 110 

 Centigrade and maintain this temperature for an hour. Weigh 

 again. The loss shows how much water was evaporated. Now 

 heat the remainder to a red heat and maintain for an hour. The 

 loss this time shows the amount of organic matter in this soil, and 

 the residue shows the amount of mineral matter. Figure the dif- 

 ferent values in per cents. Test a number of soils in this way. 

 What kind of soils contain the most water? v The most organic 

 matter ? 



QUESTIONS 



1. Explain how an exchange of products benefits both the 

 farmer and the manufacturer. 



2. Do field stones become larger or smaller? Why? 



3. What kind of rock is slate? Marble? Sandstone? How 

 is each kind formed? 



4. W T hat is the relative surface area of a one-foot cube of stone 

 and the same stone divided into one-half inch cubes ? 



5. What climates facilitate weathering? 



6. Where are the humus colored soils thickest, on the hills or 

 in the valleys? Why? 



7. Why are some soils red? Blue? 



8. Are there glacial boulders in your country? From where 

 did they come? Are there any evidences that glaciers once covered 

 the region? 



9. What are the necessary elements in an agricultural soil? 



10. What kind of soil predominates in your region? 



11. What is the value of air in the soil? 



12. Why are sandy soils warmer than clay soils? 



13. What is the advantage in mixing your own commercial 

 fertilizers over buying them already mixed? 



14. What determines the water capacity of soils? 



15. What crops in your region require the least rain? Name 

 some wet season crops. 



16. Should corn cultivation be deep? Why? 



