text: The Victor Meyer apparatus is the standard laboratory method for determining the molecular weight of a volatile liquid. It was developed by Viktor Meyer, who spelled his name Victor in publications at the time of its development. In this method, a known mass of a volatile solid or liquid under examination is converted into its vapour form by heating in a Victor Meyers tube. The vapour displaces its own volume of air. The volume of air displaced at experimental temperature and pressure is calculated. Then volume of air displaced at standard temperature and pressure is calculated. Using this, mass of air displaced at 2.24 × 10 m of vapour at STP is calculated. This value represents the molecular mass of the substance. The apparatus consists of an inner Victor Meyers tube, lower end of which is in form of a bulb. The upper end of tube has a side tube that leads to a trough filled with water. The Victor Meyers tube is surrounded by an outer jacket. In the outer jacket, a liquid is placed, which boils at a temperature at least 30 K higher than the substance under examination. A small quantity of glass-wool or asbestos pad covers the lower end of the Victor Meyers tube to prevent breakage, when a glass bottle containing the substance under examination is dropped to it