Characteristics of Liquids. — The molecules of a liquid at rest are displaced by the slightest force, and for this reason a liquid has no shape of its own but takes the shape of the containing vessel. Hence, liquids yield to a continued application of force that tends to deform them or to change their shape in any way. They, however, manifest wide differences in their readiness to yield to distorting forces. Water, alcohol and ether are very mobile liquids, which yield readily to forces tending to change their shape. Glycerin is less mobile, and tar is still less so.
There is no sharp line of separation between liquids and solids. In warm weather, paraffin candles yield under their own weight and bend double. Although shoemaker’s wax will break readily when cold, it behaves like a very viscous liquid at higher temperatures. All liquids offer large resistance to forces tending to change their volume. For example, it requires a pressure of 1,500 lb per sq in, to cause the volume of water to change 0.5 per cent.