THE TEMPERATURE OF THE SOIL 33 



have time, test with the thermometer to see if your answer 

 is correct. Summarize your answers into a short story 

 about the influence of air space upon the temperature of 

 soils. 



21. How the Moisture in a Soil afiects its Tempera- 

 ture. — We all know that a wet, soggy soil, which is filled 

 with free or gravity water, is much colder in the spring 

 than is a well-drained soil, which contains only film mois- 

 ture. Let us investigate this with our thermometers. 



EXERCISE 13 



Object. — To show the influence of the amount of mois- 

 ture m a sou upon its temperature. 



Procedure. — Fill two cans from the same sample of 

 soil ; that is, with soil from a fence row, from a cultivated 

 field, or from a garden as you may choose. Add water to 

 the first can until it stands at the surface of the soil. 

 Add none to the second can. Plunge the bulb of a ther- 

 mometer about an inch below the surface of each soil. 

 Prepare a table as you did in the preceding exercise, but 

 substituting the words " saturated soil " and " dry soil " 

 for " sand " and " clay." Place the cans where both the 

 sun and the wind will strike them. 



Conclusions. — Men often wrap a piece of a sack about 

 a jug in the summer time to keep the water cool. The 

 sack is usually kept moist so that water is evaporating 

 from it all the time. Evaporation is a cooling process. 

 In which soil did the thermometer read lower, that which 

 was saturated, or the other one? Why? What is one 

 of the great benefits of tile draining? Which soils will 

 allow ready passage of water through them, those con- 

 taining plenty, or little, of humus? Why? Sandy soils, 

 or clay soils? Why? 



