Hofmann Method - Determination of Molecular Mass

The method is applied to those substances that are not stable at their boiling points, but that may be volatilised with no decomposition under less pressure. A known mass of the substance is vaporised above a mercury column in a barometric tube and the volume of the vapour formed is recorded. After that it is reduced to NTP (Normal Temperature and Pressure) conditions. The molecular mass of the organic substance can be measured by the application of following relationship,

Mol. Mass = (Mass of the Substance/ Volume of the Vapours at NTP) *22400