Advantages of mercury are:
1. It is opaque and shining. Hence , it is easily visible through the glass.
2. It does not wet the glass.
3. It has a low freezing point and a high boiling point. It can be used over a wide range of temperatures.
4. It is a good conductor of hest, so it quickly absorbs heat to attain the temperature of the object.
5. It has a wide range of temperature expansion.