When using the centrifuge method, the total passing the 75-µm sieve is obtained by adding the dry material passing the 75-µm sieve, along with mineral matter, to the mass removed by washing.

• A. False
• B. Not specified
• C. Cannot determine
• D. The total passing the 75-µm sieve is obtained by adding the dry material passing the 75-µm sieve, along with mineral matter, to the mass removed by washing.

Answer: (D)

In the centrifuge method, you must account for every portion of material that can pass through the 75-µm sieve after processing. The fines you get from the dry sample (the material that already passes the sieve when dried) represent part of the total. The mineral matter that also passes the sieve contributes another portion, and the material that is removed by washing (fines liberated during the washing step) adds yet another portion. Adding these three parts together gives the complete amount that would pass the 75-µm sieve. This ensures you don’t miss fines that are released or carried through during washing, or those already present as dry fines.