The function of a test tube is to hold, mix or heat small quantities of liquid or solid chemicals for assays and qualitative experiments. Test tubes also serve as temporary storage for chemicals to be used in chemical experiments.
Test tubes are usually made of borosilicate glass so they can resist reaction with chemicals and withstand temperature changes without breaking. Some test tubes are made from plastic and in most cases they are disposed of after use unlike the ones made from glass.
Test tubes come in several sizes and shapes. The standard laboratory test tube size measures 18 x 150mm. Test tubes that come without a lip are called culture tubes. They are usually used in biology for culturing live organisms such as bacteria, molds and seedlings. In medicine, culture tubes are used to store fluids and samples of blood.
Boiling tubes are essentially scaled-up test tubes. They are wider than normal test tubes to allow substances to boil violently. Other test tubes have stoppers or screw caps and these are the types that are used for temporary storage of biological samples or chemicals. Test tubes are also used for casual uses outside the laboratory environments where they can function like containers for holding a variety of items.