Liquids have no definite length or area. But it has definite volume. If the temperature is increased its volume increases. So, the expansion of liquid means the expansion in volume of the liquid. The rates of increase in volume of all the liquids are not the same. Different liquids having the same volume expand differently for the same rise of temperature.
A number of long necked glass bulbs of equal volume and size are taken. Equal volume of water, alcohol, kerosene, ether etc are taken in these bulbs (figure). Now water at room temperature is taken in a comparatively larger vessel and the bulbs are placed vertically in it. The upper level of the liquids in all the bulbs will be the same.
Now some hot water is pou-re. d into the vessel. After some time the bulbs will attain a higher temperature and it will be seen in the stem of the bulbs the upper level of different liquids are not at the same height rather their heights are different. So, it is understood that the volumes of different liquids of same volume expand differently for a definite increase of temperature.