Diagram of apparatus for an evaporation experiment: If a watch-glass be placed on a cork with sulphuric ether on the glass and water underneath the glass, as shown in the figure, the water may be frozen almost immediately by simply blowing a steady stream of air over the surface of the ether. The vapor-tension of ether is high even at ordinary temperatures, so that evaporation is rapid. Since the latent heat of the vapor is derived from the heat in the ether, glass and water, the water is quickly frozen.