AASHTO T88:2013 Standard Method of Test for Particle Size Analysis of Soils.
4.1. A solution of sodium hexametaphosphate shall be used in distilled or demineralized water, at the rate of 40 g of sodium hexarnetaphosphate per liter of solution.
4.1.1. Solutions of this salt, if acidic, slowly revert or hydrolyze back to the orthophosphate form with a resultant decrease in dispersing action. Solutions shall be prepared frequently (at least once a month) or adjusted to pH of 8 or 9 by means of sodium carbonate. Bottles containing solutions shall have the date of preparation marked on them.
5.1. The masses of subsamples and size fractions in the hydrometer analysis and hygroscopic moisture determination shall be determined to the nearest 0.01 g. The mass of the subsample for mechanical analysis of the fraction retained on the 4.75-mm sieve, the 2.00-mm sieve, or the 0.425-mm sieve for coarse sieve analysis, and each size fraction in the coarse sieve analysis. shall be determined to within 0.1 percent of the mass of the subsample. For example, a subsample with a mass of 1000g. its size fractions in the coarse sieve analysis, must be weighed to the nearest gram.
6.1. The test sample for particle size analysis shall be prepared in accordance with either R 58 for Dry Preparation of Disturbed Soil and Soil-Aggregate Samples for Test, or T 146 for Wet Preparation of Disturbed Soil Samples for Test. The representative portion of the original air-dry sample selected for test shall be weighed. The mass of this sample shall be sufficient to yield quantities for particle size analysis as follows:
6.1.1. The minimum amount required of material retained on the 4.75-mm sieve, the 2.00-mm sieve, or the 0.425-mm sieve depends on the maximum particle size, but shall not be less than the amount shown in the following table:
6.2.2. Alternate Method Using 2.00-mm (No. 10) Sieve—The sample shall be separated on the 2.00-mm sieve as described in Section 5.2.1 of R 58. The portion retained on the 2.00-mm sieve after the second sieving shall be processed in accordance with Section 7, Sieve Analysis of Fraction Retained on 2.00-mm (No. 10) Sieve. The portion passing the 2.00-mm sieve in both sieving operations shall be weighed and prepared as described in Section 6.2 of R 58. Subsamples for hygroscopic moisture, hydrometer analysis, and sieve analysis shall be weighed immediately or placed in air-tight containers until tested.AASHTO T88 pdf download.