Test tubes, commonly used instruments in chemical laboratories, are used as reaction containers for a small amount of reagents. They should be preheated before heating at normal temperature or heating, otherwise the test tubes will burst easily.) Use. Test tubes are divided into ordinary test tubes, test tubes with branches, centrifugal test tubes, etc. The specifications of ordinary test tubes are expressed in outer diameter (mm)× length (mm), such as 15 × 150, 18 × 180, 20 × 200, etc.