What is NOT a use of a test tube?

A test tube is a versatile piece of laboratory glassware primarily designed for conducting experiments, mixing liquids, and observing chemical reactions. Each of the possible uses listed has specific purposes in a laboratory setting.

Mixing liquids is one of the fundamental uses of a test tube, as its shape allows for easy agitation and blending of different solutions. Heating substances is also a common practice with test tubes, as they can be placed in a flame or a water bath without significant risk of breakage, making them suitable for experiments that require heating.

On the other hand, storing chemicals in a test tube is less practical, as test tubes typically do not have caps or closures that allow for secure long-term storage. While solids can be placed in a test tube, this is usually not their intended primary function. Test tubes are more suitably designed to hold and contain liquids, and their narrow shape is not ideal for solid materials or prolonged storage tasks. Therefore, the answer pertains to a use that is not commonly associated with test tubes in laboratory contexts.