44 PHYSICAL CONSTITUTION OF SOIL 



Wisconsin soil to a depth of 6 ft., and determined the weight 

 of dry soil in each foot. One set of determinations will be 

 found in Table IX, p. 70. The first foot of soil, a loam, is seen 

 to weigh 76-8 Ib. per cubic foot; while the fifth foot, a fine 

 sand, weighs 116-7 lb. We have here the lighter weight 

 of the loam, and the heavier weight of the sand, both exag- 

 gerated by the position in which they occur ; the loam being 

 at the surface, and lightened by tillage and vegetation, while 

 the sand is consolidated by the weight of the four feet of soil 

 which lie above it. In a later set of determinations (Wis- 

 consin 8th Rep., 107), the weights vary from 79 Ib. per cubic 

 foot for the surface foot of loam, to 1 1 1 Ib. for the fifth and 

 sixth foot of pure sand. The results furnished by experi- 

 ments at Rothamsted and Woburn will be found on p. 47. 



Anything which tends to diminish the proportion of empty 

 space in a soil, as the presence of stones, or a considerable 

 variety in the size of the particles, leading to closer packing, 

 will tend also to increase the volume weight ; while anything 

 tending to loosen the texture of the soil will diminish it. 



Weight of Soil per Acre. It is important for many pur- 

 poses of calculation to be acquainted with the weight of dry 

 soil in a given depth per acre ; to ascertain this fact it is 

 necessary to remove definite volumes of the soil, and to dry 

 and weigh them. The accurate information on this head is 

 not very extensive. 



The best mode of operation is to drive into the land a short, 

 wide steel tube, sharpened at its lower edge, till the top is 

 level with the surface ; the contents of the tube then furnishes 

 a sample of the soil to the depth represented by the length 

 of the tube. The tube should not have a diameter of less 

 than six inches ; with narrow tubes, the resistance to the 



