Grain-Size Analysis of Soil (Including Both Mechanical and Hydrometer Analyses) - Soil Properties: Testing, Measurement, and Evaluation - page 123

correction factor is computed by dividing the oven-dried mass by the
air-dried mass.
Dispersion of Soil Sample
The soil sample to be used in the hydrometer test must first be dispersed
in order to eliminate particle coagulation. This is accomplished by mix-
ing the soil with a sodium hexametaphosphate solution and stirring the
mixture thoroughly. (For specific details, see the step-by-step procedure
given shortly.)
Hydrometer Test
After dispersion, the soil-water slurry is transferred to a glass sedi-
mentation cylinder and agitated manually. The cylinder is then placed
in a convenient location, and hydrometer readings are taken at specific
time intervals until 24 h have elapsed. (For specific details, see the
step-by-step procedure, which is given subsequently.) The grain-size
distribution is determined from computations using the hydrometer
readings as a function of time. (This will be explained in the section
“Calculations.”)
Sieve Analysis
After the last hydrometer reading has been made, the suspension is
transferred to a No. 200 sieve, washed, and oven-dried. The sample that
is retained on the No. 200 sieve is subjected to a sieve analysis, normally
using No. 10, 40, 100, and 200 sieves. This gives a grain-size analysis for
that portion of the original sample that passed through the No. 10 sieve
but was retained on the No. 200 sieve.
There may be some overlapping of grain-size distribution of the
portion that passed the No. 10 sieve but was retained on the No. 200
sieve, as determined by hydrometer readings and by sieve analysis.
The actual step-by-step procedure for dispersion of the soil sample,
the hydrometer test, and the sieve analysis of the portion passing the
No. 10 sieve is as follows (ASTM D 422-63 [Reapproved 2002] [1]):
(1) When the soil is mostly of the clay and silt sizes, weigh out a
sample of air-dried soil of approximately 50 g. When the soil is
mostly sand, the sample should be approximately 100 g.
(2) Place the sample in a 250-mL beaker and cover with 125 mL of
sodium hexametaphosphate solution (40 g/litre). Stir until the soil
is thoroughly wetted. Allow to soak for at least 16 h.
(3) At the end of the soaking period, disperse the sample further,
using a mechanically operated stirring apparatus. Transfer the
soil-water slurry from the beaker into the special dispersion cup
shown in Figure 10-2, washing any residue from the beaker into
the cup with distilled or demineralized water (Note 1). Add distilled