If you are looking for a dipersing agent for hydrometer testing, there is a specific compound. It is the same compound that is the active ingredient in calgon dishwashing soap. You want to use the same material in the specified conentration, or it will mess up the hydometer. The procedure is detailed in the ASTM spec.
Dear expert members, So far I understand ..... For hydrometer testing, pH of the soil should be measured to know wheather it is alkaline or acidic soil. If the soil is acidic then dispersing agent should be alkaline, and vice versa. But how to select the concentration of the dispersing solution? Suppose.. at first: I may prepare the solution using 30gm sodium hexametaphosphate with 1000ml water; next I may prepare the solution using 40gm sodium hexametaphosphate with 1000ml water and so on...
No. The dispersing agent for hydrometer analyses must be prepared at a specific concentration to ensure uniformity of tests. The pH of the soil does not (as far as I know) enter into consideration for the dispersing agent used for this test.
If you are asking about a dispersant for some other purpose or test, then you will need to be clear about what your intention is.
The ratio for the dispersing agent used for a hydrometer test per ASTM D422 is 40 grams of Sodium Hexametaphosphate to 1000 ml of distilled water. Make sure you have a good mixure becuase when the Sodium Hex get wet it tend to clump. The pH is only necessary to measure if your dispersion agent is sitting not be used for great lenghts of time ie greater than one month.
