92 NATURE AND PROPERTIES OF SOILS 



ened through tillage, it becomes lighter for any given volume. 

 The addition of organic matter has the same effect, since the 

 particles are spread wider apart and the air and water spaces 

 increased. The specific gravity figure of a sandy loam of 1.55 

 may readily be lowered to 1.45 by an increase of organic 

 material. Some loams high in organic matter may drop as 

 low as 1.1 in specific gravity while muck often reaches the 

 low figure of .40. 



In the field the volume weight of a soil may be estimated by 

 driving a cylinder of known volume into the ground and ob- 

 taining thereby a core of natural soil. By weighing the soil 

 and then determining the amount of water that it holds, the 

 amount of absolutely dry soil may be ascertained. Dividing 

 this by the weight of an equal volume of water gives the figure 

 for volume weight.^ 



A laboratory determination may be made by putting the 

 soil into a receptacle of known volume and weighing it. From 

 the weight of the absolutely dry soil and the weight of an 



^ The rubber tube method has proven very convenient for the field de- 

 termination of volume weight. A hole is bored in the soil to the required 

 depth by a specially constructed auger, the soil being carefully removed 

 and later oven dried. A very thin-walled tubular rubber bag of the size 

 of the auger hole is carefully inserted in the hole previously bored. The 

 tubular bag is then filled with water flush with the surface of the soil. 

 The water is measured and the volume of the soil removed is thus de- 

 termined. Knowing the weight of dry soil and its original volume, the 

 volume weight may be calculated. The experimental error of the method 

 is rather low. 



Israelsen, O. W., A New Method of Determining Volume Weight; 

 Jour. Agr. Res., Vol. XIII, No. 1, pp. 28-35, April, 1918. 



The paraffin-immersion is valuable with heavy soils. Small pieces of 

 soil are dried, weighed and then coated very thinly with paraffin, just 

 sufficiently to prevent the entrance of water, yet not enough to intro- 

 duce serious experimental error. The weight of the water displaced by 

 a number of such pieces may be determined easily by the use of a 

 graduated cylinder. 



Shaw, C. P., A Method for Determ%mng the Volume Weight of Soil 

 in Field Condition; Jour. Amer. Soc. Agron., Vol. IX, No. 1, pp. 38-42, 

 1917. See also, Trnka, R., Mine Studie uber emige physikalishchen 

 Bigenschaften des Bodens; Internal Mitt, of Bodenkunde, Bd. IV, Heft 

 4-5, S. 36S-380, 1914. 



