Double Hydrometer - Sample Size

[Arizona3106]

I'm really confused here.

I will be running the double hydrometer test (ASTM D4221). Section 8.1 says to use 50g of oven dried soil to run a normal D422 hydrometer test. However, 8.3 says to run the test without any dispersing agent or mechanical agitation using only 25g of oven dried soil.

Is this right - Run the normal one with 50g and the other one with 25g???? I don't understand the huge difference in sample weight when the calcs seem to indicate that the results can be directly compared.

I did run one, and for the test with no dispersing agent, my hydrometer reading was 0, and the zero correction in the blank cylinder was 5. My corrected hydrometer readings are now negative. I'm not sure how this could have happened, even using only 25g of sample

 

[Arizona3106]

OK - I have heard from others that you do use 25g for the water only hydro, and that 0 readings are not unusual. I would still like some explanation as to why you should use half the amount of soil for the sample that is not mechanically agitated with dispersing agent.......