Victor Meyer apparatus

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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.

The apparatus consists of a vertical glass column contained in a steam jacket, with a small bed of sand in the bottom of the column to protect its glass base. A delivery tube leads from the top of the column to a gas jar in a hydralic trough. At the top of the column, a small glass phiall with a ground glass stopper and containing a weighed quantity of the liquid to be tested rests on a device called the spoon, which can be rotated to release the phiall.

When the spoon is rotated, the phiall drops to the bottom of the column. The liquid vaporises, ejecting the stopper from the phiall and displacing a volume of air equal to the volume of the vaporised liquid at 100°C, the temperature being controlled by the presence of the two phases of water in the steam jacket. This air is collected in the gas jar, and its volume measured.

Knowing both the mass of the sample of liquid and its volume as a gas at the temperature at which the air is collected (room temperature) the molecular weight can then be calculated.