A meniscus is the curved top surface of a column of liquid. The meniscus can be either concave or convex.

A concave meniscus occurs when molecules are more attracted to the container than to each other. The liquid appears to ‘climb’ the sides of the container. Most liquids possess a concave meniscus.

There are 2 test tubes containing different liquids. The test tube on the left contains water. A line is drawn at the level of the liquid. The liquid is over the line at the sides of the test tube to make a concave meniscus. The test tube on the right contains mercury, a metal that is a liquid at room temperature. A line is drawn at the level of the liquid. The liquid is below the line at the sides of the test tube to make a convex meniscus.

Figure: Concave and convex meniscus

A convex meniscus is the opposite of a concave meniscus. An example of a molecule with a convex meniscus is mercury. A flat meniscus is possible when the container is made of certain types of plastic or material that the contained substance does not stick to.