Test tubes serve as reaction vessels for small quantities of reagents

Author:Orginal from Internet

A test tube is a common piece of laboratory glassware used as a reaction vessel for small amounts of reagents. It can be used at room temperature or while being heated (note that the tube must be preheated before applying direct heat to prevent it from cracking or shattering). There are various types of test tubes, including standard test tubes, side-arm (branched) test tubes, and centrifuge tubes. The specifications for standard test tubes are indicated by their outer diameter (mm) × length (mm)—for example, 15×150, 18×180, or 20×200.

1. Ensure the outer surface of the test tube is dry before heating. Always preheat the tube evenly using an alcohol lamp before applying concentrated heat.

2. Do not touch the test tube directly with your hands while it is being heated; use a test tube holder or secure the tube to a laboratory stand (retort stand).

3. When heating solid substances, the mouth of the test tube should be tilted downward to prevent any condensed water from flowing back, which could cause injury.

4. When using a test tube holder, slide it on from the bottom of the tube to a position approximately one-third of the way from the opening. This prevents damage to the rim of the test tube and protects the holder from being scorched.

5. When collecting gas via the water displacement method, always remove the delivery tube from the water before extinguishing or removing the alcohol lamp. Failure to do so may cause water to be drawn back into the hot test tube, leading it to crack or shatter.

6. Because test tubes come in various sizes, ensure that the volume of liquid inside does not exceed one-third of the tube's capacity when heating. If the contents are not being heated, the liquid volume should not exceed one-half of the tube's capacity.

7. Do not submerge a heated test tube in cold water, as the sudden temperature change (thermal shock) can cause it to crack or shatter. 8. When heating a liquid, the opening of the test tube should be pointed diagonally upward, away from any people. To maximize the surface area exposed to heat, the tube may be tilted at a 45-degree angle.

Although a test tube is a piece of laboratory glassware that can be heated directly, students must exercise caution during use to prevent any accidental personal injury.