Using pycnometry and Archimedes’ principle to measure the gross and air cavity volume of fruit

A technique based on Archimedes’ Principle is described for measuring the volume of small objects (0.5–5 cm3) less dense than water. The volume of 10 small red chillies was measured by pycnometry and an immersion Archimedes technique which involved suspending the chillies in water in a container placed on an electronic balance. A pycnometer, which uses helium gas is able to determine the internal solid volume of the chillies and water immersion the outer volume. The difference between the two volumes gives the volume of internal air cavities in the chillies. The pycnometer and immersion techniques were compared by measuring the volume of wax candles with volumes between 0.3 and 2.5 cm3. A Bland-Altman analysis revealed that the Archimedes volumes were lower than pycnometry volumes by 6.1±2.3% which needs further investigation. A combination of pycnometry and water immersion may be a useful tool for botanical studies.