Next PageCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> Atech Center - Hydrometer Procedure

Calculations

Step I. Percentage of Hygroscopic Moisture in Sample (%M)

% M = [W - W1/W1]100

where:

W = mass of air dried soil

W1 = mass of oven dried soil

Example: Mass of air dried soil (W) is 37.58 grams. Mass of oven dried soil is 37.28 grams.

%M = [(37.58-37.28)/37.28]100

%M = (0.3/37.58)100

%M = (0.0079)100

%M = 0.79

Step II. Percentage of Soil in Suspension (for Hydrometer 152H)

P = (Ra/w)100

where:

P = Percent of originally dispersed soil in suspension

R = Corrected hydrometer reading

w = Mass of dispersed soil (oven-dried basis)

a = Value for density of suspension, derived from Table 1

Table 1. Values of a for Different Specific Gravities

Specific Gravity, G (apparent)

Constant, a
2.92
0.94
2.85
0.96
2.75
0.98
2.65
1.00
2.55
1.02
2.45
1.04
2.35
1.06

Use a value for nearest G of soil

Example: Actual reading of hydrometer was 38.0. Composite correction value was 7.5. Corrected hydrometer reading (R) is therefore 38.0 - 7.5 = 30.5. Value for a derived from sample's apparent specific gravity (2.65), = 1.00. Mass of dispersed soil (w) on oven dry asis is 81.09.

P = (30.5 X 1.00/81.09) 100

P = (30.5/81.09) 100

P = (0.3761) 100

P = 37.6%

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