High precision balance from salt and water and the slow swelling of ping-pong balls

Research output: Article

2 Citations (Scopus)


Density gradient columns are the most accurate type of equipment for determining unknown densities. Commercial equipment is designed for chemical engineering practice, where the typical sample size hardly exceeds a few grams. The accuracy of measurements crucially depends on the precision of height determination. Here we demonstrate that stratified salt water in much larger containers (used for experiments in geophysical fluid dynamics) is perfectly suitable for accurate density measurement of large samples. Even height determination has an increased reliability because the large free fluid surface serves as an excellent calibration level. The efficiency is illustrated by revealing a subtle effect where celluloid ping-pong balls slowly absorb water and swell, changing the total density by a few thousandths only.

Original languageEnglish
Pages (from-to)303-310
Number of pages8
JournalEuropean Journal of Physics
Issue number2
Publication statusPublished - márc. 1 2004


ASJC Scopus subject areas

  • Physics and Astronomy(all)

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