1. The vapor pressure, above the surface of a liquid, is independent of whether the space contains a gas or is a vacuum.
   2. The vapor pressure of a mixture is equal to the sum of pressures of the separate vapors (gases)

      In this apparatus, in the Garland Collection of Classic Physics Apparatus at Vanderbilt University, the two tubes are connected at the bottom. Drops of a liquid are introduced into the rear column, and the corresponding vapor pressure is measured by mercury levels in both columns. As the operation is rather involved, reference is made to the 1875 edition of Ganot's Physics, pp 298-299. 

   The apparatus was probably obtained by Vanderbilt ca. 1875.