Page 28 - Curriculum Visions Dynamic Book

waterproof membrane such as a sheet of polyethene is inserted within the brickwork of a house just above ground level. It is called a damp- proof layer.
In a closed upright tube where the space above the water is a vacuum, capillarity will cause water to rise up the tube until the weight of water balances atmospheric pressure. As a result, a column of water like this can be used as a barometer. In fact, the height is so great (just under 10m) that another and heavier liquid – mercury – is used to make barometers a more usable size.
(Above) Damp-proof membrane in a house wall.
(Above) When oil and water are put together, the water and oil separate because they are immiscible, with the more dense water sinking below the less dense oil.
Immiscibility
The surface-tension effect applies not just to water droplets in air but also
to water in a liquid with which it does not mix. This kind of liquid is called immiscible. Oil is an example. When water is dripped into oil, it makes globules, which then sink to the bottom of the oil.
Waterproofing and wetting
agents
The surface tension effect is so strong in water that it is sometimes difficult to get water to enter a material, especially if it is dry. This effect can be put to good use by making an umbrella,
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