Determine the mass of a sub-portion of the material passing the 2 mm (#10) sieve for hygroscopic moisture content. Hygroscopic moisture is simply the moisture in equilibrium with that in the atmosphere to which the soil is exposed. All associated masses for hygroscopic moisture should be recorded to the nearest 0.01g. Follow AASHTO T265, Laboratory Determination of Moisture Content of Soils, in order to determine the moisture content.

Figure 5. Sample appearance after 12 hour soaking period.

After weighing, samples for the hydrometer test need to be dispersed by being placed into a 250mL beaker, and covered with 125mL of stock solution (prepared concentration of sodium hexametaphosphate, 40 grams per liter), stirred thoroughly with a glass rod and allowed to soak for a minimum of 12 hours (Figure 5).

Figure 6. Placing sample into dispersion cup

After the 12 hour soaking period, empty the contents of the beaker into the dispersion cup. Make sure all of the sample in the beaker is washed into the dispersion cup (Figure 6).

Figure 7. Disperse sample for 60 seconds.

Add distilled water into the dispersion cup so that it is at least half full. Disperse the contents in the cup mechanically for a period of 60 seconds (Figure 7). T 88 also presents alternate methods for dispersion of the sample not discussed in this text.