Option 1  

(Uses simpler techniques)

The following link uses the LaMotte soil texture unit code 1067.  Permission was granted from LaMotte for our use.  

If you decide to use option 1, you will need to purchase their kit, which includes all the supplies needed to determine soil texture.  Go to www.lamotte.com for further information.

1.  Sieve air-dried soil sample through 2mm mesh.

2.  Obtain 150g of air-dried soil sample.

3.  Transfer sample in to a 1L beaker and add 75ml of 10%   Na-hexametaphosphate solution (a dispersing agent).

4.  Add 750ml of distilled water (dH₂O) in to the beaker and mix for two minutes.

5.  Transfer contents in to a 1L Bouyoucos cylinder.  Remove all remaining particles adhering to the bottom of the beaker with a squeeze bottle filled with dH₂O.  

6.  Fill cylinder to the 1000ml mark and, in another cylinder, run a blank with dH₂O and the 75ml of 10% Na-hexametaphosphate solution.

8.  Wash the hydrometer with the dH₂O from a squeeze bottle, gently dry, and return it to its case to prevent damage.

9.  Stir the sample in suspension and gently insert the hydrometer in to the mixture after 30 seconds.

10.  Steady the hydrometer and read, on the hydrometer stem, the weight of silt and clay particles at exactly 45 seconds, using Stokes' law: v(cm/s) = 8711D², where 8711 is constant (derived from values for acceleration due to gravity, particle, density, temperature, and viscosity) and D = particle diameter (assuming particle sphericity).  From Stokes' Law and the equation "distance = (rate)(time)", it is derived that 45 seconds are required for all the fine sand (>0.05mm) to settle out of suspension.

11.  Remove the hydrometer and return it to its case to prevent damage.

13.  Rinse all glassware and place on drying surface.

14.  Recording the results of particle-size analysis:

   Soil Sample: __________

    a.  Soil sample in 1L cylinder (g)   __________
    b.  Hydrometer reading after 45s. __________
    c.  Hydrometer reading after 6hr. 52min. __________
    d.  Corrected hydrometer readings   45sec. __________  6hr. 52min __________
                    subtract the blank solution reading from the uncorrected hydrometer reading
    e.  Silt and clay in suspension (g)  __________
    f.   Sand in sample (g)  __________
    g.  Clay in sample (g)  __________

  % sand = 100 - (R_45s - R_L) x 100/sample wt.

  % clay = (R_~7hr - R_L) x 100/sample wt.

  % silt = 100 - (% sand + % clay)

     - where R_L = 1.006 at 45sec.
                       = 1.0055 at  ~7hr

After determining the percent of sand, slit and clay refer to the Soil Textural Triangle