§ 107. THE PHYSICAL QUALITIES OP THE SOIL. 197 



the water will rise in 24 or 48 hours ; it will be found 

 to rise more slowly in humus and clay soils than in light, 

 sandy ones. 



5. The rapidity with which water will make its way 

 downwards in the soil may be determined in the same 

 tube, partly filled with a fresh quantity of earth ; fill the 

 tube above the soil with water to the depth of 4-8 cm., 

 and note the time required until it has reached a given 

 depth, or how soon the water disappears from the surface 

 of the soil, r.nd also how far a given quantity, that is in- 

 sufficient to make its way through and moisten the soil 

 quite to the lower end, will penetrate downwards. 



It will be found that the same quantity of water will 

 go furthest in a fine loam or a sandy soil. 



c. The Relation of the Soil to Heat. — 1, To 

 determine the power of the soil to ahsorh heat, fill a 

 cubical zinc box, about 6 cm. square, with soil, expose it 

 several hours to the direct rays of the sun on a hot day, 

 carefully observe the temperature in the sun during the 

 experiment, and the elevation of temperature in the up- 

 permost centimetre of the soil. The zinc box should be 

 inclosed in a box of thick pasteboard, and this in a wooden 

 box, to prevent access of heat at the sides. 



It may also be interesting to observe the heating power 

 of the sun's rays on the soil, while it is in a more or less 

 moist condition, say with 5, 10, or 20° 1^ of water, more 

 than that naturally present in the soil. Such determina- 

 tions may be made by exposing about 50 grnis. of the 

 moistened soil for several hours in a glass flask to the 

 direct rays of the sun, and noting the changes of tem- 

 perature. 



2. The power of the soil to conduct heat may be de- 

 termined by putting the same box, as used in the previ- 

 ous experiment, into hot water, and observing how long 

 a time elapses before the temperature of the earth in the 



