Which statement about the constant mass procedure is true?

• A. Constant mass testing is performed using an oven regulated at 150 °F.
• B. Constant mass testing is performed using an oven regulated at 110 ± 5 °F.
• C. Constant mass testing uses no oven.
• D. Constant mass testing uses a different procedure.

Answer: (B)

Moisture content is determined by drying a sample until its mass stops changing. In the constant mass procedure, you heat the sample in an oven kept at about 110 ± 5 °F, then weigh it after cooling to a constant mass. The idea is to drive off only the moisture, not other components, so the weight stabilizes and you can calculate how much moisture was present from the initial versus final mass.

Using this specific moderate temperature is important: it’s hot enough to remove water efficiently but gentle enough to avoid damaging the sample or driving off other volatile substances that would skew the results. If the oven were hotter, you could alter the material; if it were cooler or not heated at all, moisture wouldn’t be removed reliably and the mass wouldn’t stabilize, making the measurement inconsistent.

So the essence is: dry in a controlled oven around 110 ± 5 °F, cool and reweigh until the mass is constant, and use the difference to determine moisture content.