Soil Texture-Hydrometer method

By Jared L. DeForest

Materials – Dispersing Agent

In 1 l flask (enough for 10 samples)
50 g sodium hexametaphosphate
Bring to approximate volume with distilled water

• 250 ml Erlenmeyer flask
• Electric blender (milkshake machine) with metal cups
• Glass sedimentation/graduated cylinder (1 liter) Stopwatch/timer
• Soil hydrometer (ASTM 152H)
• Amyl alcohol

Procedure

Add the following to 250 ml Erlenmeyer flask

• 40 g Oven-dried equivalent air dried, sieved soil
• 100 ml Dispersing agent

Place on orbital shaker (150 rpm) overnight.

Swirl mixture then quickly transfer into metal blender cup, using tap water from a squirt bottle to rise out all the soil particles. Add tap water to the blender cup to 2/3 full and blend for 5 minutes on high speed.

Transfer the soil slurry into cylinder and use squirt bottle to rinse out ALL soil particles. Fill the cylinder to the 1 liter mark with tap water. Allow the suspension to equilibrate to room temperature.

Set up a blank cylinder with just tap water with 100 ml of the dispersing agent to the 1 liter mark. This blank reading (R_L) will be used to correct your hydrometer readings.

Thoroughly mix the suspension using the metal plunder for 30 seconds. Be careful when doing this to avoid splashing any of the solution and soil particles out the top! Remove the plunger and immediately note the time.

Gently ease the hydrometer into the cylinder and after exactly 45 seconds (R_45s), take the hydrometer reading. If foam obscures the reading, add 1-2 drops of amyl alcohol. After taking the 30 second reading, do not move or disturb the suspension.

An hour and a half after stirring carefully insert the hydrometer and take a reading (R_1.5h). At least 24 hours after stirring, carefully insert the hydrometer and take a reading (R_24h).

Created: 01/28/11; Revised: 10/10/11