The true density test method is using the “Gas replacement method”- based on the of Archimedes principle-gas expansion displacement method, the use of small molecules of inert gas (helium or nitrogen) under control conditions of the Law of Bohr (PV=nRT), By measuring the decrease in gas volume of the test chamber caused by the sample being placed in the test chamber, the true volume of the test sample is calculated, and the true density is analyzed.

Pressurized target pressure of the displacement gas into reference volume chamber (a known volume). after pressure stabilized, recorded the pressure. And then opened valve allowing the gas to expand into sample chamber whose volume is also know. Once pressure stabilized, recorded this second pressure. This pressure drop ratio is then compared to the behavior of the system when a known volume standard underwent the same process.