Moisture content and physical condition of soils . l rodsG, spaced to allow afree movement of thebeam between and M2 are clampsthat check the up-and-down movement of thebeam. The depth to which the point penetrates is determined bythe position of M2. The measurement is always begun at the sameheight—the level of the cup, which was also the soil level—and weightis added until the beam reaches J/2, by which time the tool has pene-trated 6 centimeters into the soil. The approach of the beam to , isobserved by means of a small mirror R fastened at an angle to M2. In making a penetration
Moisture content and physical condition of soils . l rodsG, spaced to allow afree movement of thebeam between and M2 are clampsthat check the up-and-down movement of thebeam. The depth to which the point penetrates is determined bythe position of M2. The measurement is always begun at the sameheight—the level of the cup, which was also the soil level—and weightis added until the beam reaches J/2, by which time the tool has pene-trated 6 centimeters into the soil. The approach of the beam to , isobserved by means of a small mirror R fastened at an angle to M2. In making a penetration measurement the procedure is to make upa large soil sample to the desired water content, which is then deter-mined accurately by drying a sample at 110° C. and calculating ns percent on the dry weight of soil. This method makes the different watercontents of the same soil comparable one with another. The totalsample is well mixed by screening and placed in a tightly coveredpail. This holds enough soil to permit of repeating the measurements. 10 20 30 40 50 pack/kg paessope ( ms pep sq cm.)Fig. 29.—Penetration-packing results. 64 MOISTURE CONTENT AND CONDITION OF SOILS. several times without twice using the same portion of soil. This isessential because a wet soil dries out quite rapidly when exposed tothe open air, particularly during screening. By using a fresh portioneach time successive measurements are made there will be but slightdifferences in the water content of the different samples. The soil isthen leveled to the top rim by cutting off the extra material in such away that no packing results, after which it is pressed, if desired, inthe packing machine, the rim removed, and the soil again cut off tothe level of the top of the cup. The penetration measurements arethen made; generally three trials for each sample. The} should bemade at points the same distance from the rim of the vessel and equaldistances apart. This condition is easily attained by drawing onthe
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