This movie represents how to measure the vapor pressure of a liquid.
Here are more details as to what is happening in this video.
At 0 seconds: the apparatus shows three tubes that had originally been completly filled with Hg, inverted and placed into a reservior contain more Hg. The level of the Hg drops to a height that is determined by the magnitude of the pressure exerted by the atmosphere is called the atmospheric pressure. The symbol Patm shown adjacent to the left most barometer denotes this height, which at sea level is normally 760 mmHg or 1 atmosphere.
At 3 seconds a syringe appears and injects a sample of water into the tube on the left. Watch as the water, which is less dense compared to Hg, floats to the top of the Hg column. Notice at about 10 seconds as the water is rising the level of the mercury begins to fall. This continues until 14 seconds when water begins to condense at the top of the Hg column. We understand what is happening as the initial falling of the level of the Hg is due to water vaporizing into the vacuum above the meniscus of Hg. The pressure due to the water in the gas phase exerts a pressure, vapor pressure, which pushes against atmosperic pressure to lower the height of the column of mercury. When enough water has been injected, at about 15 seconds, water begins to condense. At 19 seconds a measure appears to the new height of the Hg column, and then at about 22 seconds a measure for the vapor pressure of water. Notice on the right side of the video the vapor pressure of water is 23.7 mmHg.
At 28 seconds a sample of ethanol was added to the center column of Hg. Notice the vapor pressure of ethanol is greater than the vapor pressure of water at the same temperature. On the right side of the video the vapor pressure of ethanol is 55 mmHg.
At 51 seconds a syringe containing diethyl ether appears near the right most column of Hg and injects a samll of the liquid into the column of Hg. Pausing the video at 1 minute and 5 seconds we can see that the injected diethyl ether has vaporized and the height of the Hg has fallen quite a bit. Continuing the video additional diethyl ether is injected into the column until the pressure exerted by the diethyl ether vapor/gas gets to the equilibrium vapor pressure (the maximum pressure exerted by the vapor above its liquid) at which diethyl ether condenses to form its liquid. The equilibrium vapor pressure for diethyl ether is 520 mmHg.
This experiment allows the measurement of the equilibrium vapor pressures of water, ethanol and diethyl ether.
That diethyl ether has such a high equilibrium vapor pressure indicates that the intermolecular attractive forces in diethyl ether liquid are much weaker compared to ethanol and water.