Analytical Methods:PSD Pipette

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Particle size analysis – pipette method
based on the method of the Soil Survey of England and Wales

Equipment and chemicals1needed

 * Analytical scales
 * Thermometer
 * 25 ml long glass pipette
 * Pestle and mortar
 * Sieve stack with 2 mm, 600 &#181;m, 200 &#181;m, and 60 &#181;m sieves and sieve base.
 * Glass beakers
 * 500 ml measuring cylinder


 * Calgon: Dissolve 75 grams of sodium hexametaphosphate in 2 litres of distilled water
 * 27-30% H2O2
 * Distilled water

Safety
1 Always consult chemical safety data sheets and follow appropriate health and safety protocols before handling or using chemicals.

Many chemical saftey data sheets are available here from this Oxford University based database.

Method

 * 1) Dry the soil at 105oC in an oven.
 * 2) Pass the material through a 2mm sieve. Weigh both the greater than 2 mm fraction and the less than 2 mm fraction separately.
 * 3) Using the analytical balance, weigh out 10.000 g of sample. Record the weight to the nearest .005g.
 * 4) Transfer the sample to a tall glass beaker and add 10 ml of 30% H2O2 (WARNING!! H2O2 is a strong oxidizer and will readily react with hair, skin, eyeballs, clothes, etc.). If the reaction is vigorous add further 10ml portions of H2O2 until no reaction occurs. Record how much is added.
 * 5) When the reaction diminishes, add approximately 50 ml of distilled water and heat on a hot plate at 90oC for 1 hour. Watch carefully to prevent boil over.
 * 6) Remove from heat source and let cool.
 * 7) Place the treated solution into plastic bottles and add 10 ml of sodium hexametaphosphate (Calgon), put caps on bottles, check for leaks, and put on the shaker. Leave samples on shaker overnight (or at least 6 hours).
 * 8) Pipette 10ml Calgon into a weighed evaporating dish and dry at 105oC, reweigh and subtract the original wight of the dish to obtain the weight of the residue (R).
 * 9) Sieve the shaken soil solution through a sieve stack of 600 &#181;m, 200&#181;m, and 60 &#181;m. Rinse the residue from each sieve into a weighed evaporating dish and dry in the oven at 105oC. Rewiegh and subtract the weight of the dish to record the weight of the fine (60-200 &#181;m - FS), medium (200-600 &#181;m - MS) and coarse (600-2000 %#181;m - CS) sand sized fractions.
 * 10) Transfer the less than 60 &#181;m suspension to a 500 ml cylinder.
 * 11) The cylinder should now contain only the silt and clay fractions of the sample. Fill cylinders to the 500 ml mark with distilled water.
 * 12) Measure and record the temperature of the water in the cylinder. Consult the settling time chart to determine the time and depth at which "pulls" must be made for the various size fractions.
 * 13) Agitate the sample vigorously for 30 seconds, being careful not to introduce any air bubbles. Immediately after you cease stirring the sample, insert the 25 ml pipette and draw off a sample at a depth of 15-20 cm. Empty the pipette into a clean, dry weighed evaporating dish. Rinse the pippete twice in distilled water and add these to the dish. Dry at 105 oC in the oven and reweigh. Subtract the weight of the dish to obtain the weigth of the less than 60 &#181;m fraction(A).
 * 14) Mix the contents of the cylinder again, then leave to settle for the time appropriate to the solution temperature (see the table below).
 * 15) Using the 25 ml pipette withdraw another sample from a depth of 9 cm. again empty this into a clean weighed evaporating dish, with two rinsings from the pipette. Dry in the oven at 105 oC and reweigh. Subtract the weight of the dish to obtain the weight of the clay (less than 2 &#181;m) fraction (C).

Calculations

 * 1) Calculate the oven dry mass of peroxide-treated soil
 * Mp = (20 x A) + CS + MS + FS - R
 * 1) Calculate the percentages of particles having less than the equivalent diameters expressed on a peroxide-treated soil basis are:
 * Clay (less than 2 &#181;m) = 100 x ((20 x C) - R) / Mp
 * Silt and clay (less than 60 &#181;m) = 100 x ((20 x A) - R) / Mp
 * Fine sand, silt and clay (less than 200 &#181;m) = 100 x (1- ((CS+MS)/MP))
 * Medium sand, Fine sand, silt and clay (less than 600 7#181;m) = 100 x (1- (CS/Mp))
 * Coarse sand, Medium sand, Fine sand, silt and clay (less than 2 mm) = 100% air-dried peroxide treated soil.

Recommendations

 * 1) Depths for successive draws should be measured from the actual (declining) surface of the suspension; these depths are given by Stoke’s law without modification, regardless of whether a subsequent draw is made at lesser, equal, or greater depth than the preceding draw.
 * 2) It is very important to record the times and depths of all draws, and any restirring. If errors occur, you can back-calculate to determine the limiting particle diameter that you actually sample.
 * 3) Avoid blunders by allocating sufficient time to prepare for each group of draws, including the time to temporarily re-mark the pipette if you use non-standard depths, and to double-check that you have inserted the pipette to the correct depth.
 * 4) Allow about 10 minutes to calculate and prepare if you must change any draw times.

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