1. Holding Test Tubes: One of the fundamental purposes of a test tube rack is to stably hold test tubes. This ensures that test tubes do not slide or tip over during experiments, guaranteeing the safety and reliability of the experiment.

2. Heating Test Tubes: Test tube racks are also used for heating test tubes, especially in experiments that require the heating of test tubes. By using them in conjunction with a heater, test tubes can be securely fastened to the test tube rack, avoiding the unsafe practice of holding test tubes by hand. This also ensures that the test tubes remain level, preventing them from tipping over during the heating process.

3. Temporary Placement During Experiments: In certain experiments, it is necessary to temporarily place test tubes under specific conditions. Test tube racks can be used to position test tubes in the required locations, reducing the burden on laboratory personnel and ensuring the stability of the test tubes, preventing breakage or spillage.

4. Holding Test Tube Clamps: Test tube racks can also be utilized to hold test tube clamps. Test tube clamps are devices designed to grip test tubes, either securing them in place or suspending them. The combination of test tube clamps and test tube racks allows for the secure attachment and positioning of test tubes, facilitating experimental procedures.

In summary, chemical test tube racks play a crucial role in laboratory experiments by providing convenience and enhancing the safety and reliability of chemical experiments.