§ 107. THE PHYSICAL QUALITIES OF THE SOIL. 193 



careful observations should be made, at the same time, of 

 the temperature, the clearness of the sky, and the 

 amount of the dew-fall, and the experiment should be 

 performed over a grass plot as well as over a freshly 

 stirred soil. 



"With an average dew-fall, the amount of water taken 

 up by a soil above what it contains in the air-dried state 

 varies, with different kinds of soil, between 0.4 and l.S°\^ 

 of the weight of the completely dried soil. 



Finally, to test the effect of the depth of the soil on 

 its power of absorbing moisture under these different cir- 

 cumstances, several trays or boxes, of say ^l^, V\^^ 3, and 

 6 cm. deep, and 5 cm. square, may be filled with air-dried 

 soil, in all cases equally dry and finely j^ulverized, and 

 the whole exposed to the ordinary atmospheric influ- 

 ences, or to a saturated atmosphere, or to the night air, 

 in the manner directed above. 



By such experiments we may determine how much 

 moisture is absorbed by layers of soil of different thick- 

 nesses within a certain length of time, how far the moist- 

 ure penetrates into different soils in equal times, and how 

 long a time is required to saturate layers of different 

 thicknesses in a saturated atmosphere. 



b. The Relation of the Soil to Liquid Water i?s' its 

 Pores.— 1. To determine the power of the soil to retain 

 liquid water in its pores, construct a zinc box, 17 cm. deep, 

 and 3 cm. square, and pierce its bottom with numerous 

 small holes ; lay over this bottom a piece of moistened 

 fine linen, and weigh the box ; then put in a small quan- 

 tity of the properly dried and pulverized soil, taj) the 

 box gently on the table a few times, and proceed in the 

 same manner until the box is full, and weigh again. 

 Then immerse the bottom of the box in water to the 

 depth of 3-4 mm. ; the water appears at the surface of 

 the soil sooner or later, according to the nature of the 

 latter ; let the apparatus remain in the water until |t suf- 

 9 



