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Originally Posted by risingstar3110
It's hard to soak the water evenly inside the sponge through
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Simple. Wring/compress the sponge underwater until no more air bubbles come out, then let it absorb more water.
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Actually i think the best way to do it is measure the sponge in analytical scale (A). Then measure the weight of a cup full of liquid (full to very last drop) (B). Drop the sponge in, wait for it to sink. Clean all the water which surged out. Measure the weight of the cup with the sponge (C). Calculate volume:
V = (A+B-C)/(density of that liquid)
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Sponges don't sink by themselves unless a pressure is applied on it to sink, or the mass of water absorbed by the sponge outweighs the entire dry sponge itself, meaning which the sponge has to be really thin. The trapped air pockets totaled up will counteract to the water absorbed and let it stay afloat, similar to the concept of why wood floats on water.
Filling the cup full of liquid isn't exactly a good idea because of the molecular structure of water that result in hydrogen bonds, resulting in a less than accurate measurement of volume. Markings below the filling point are often used in Archimedes-type experiments to counteract this error when the container has a large area.
Volume/density formula is a good idea though. There should be a few more control group sets with the same sponge and liquids to get a more accurate mean value.