Burning magnesium in dry ice

Magnesium turnings and magnesium pencil sharpener burn in a cavity of dry ice blocks. Burning magnesium in dry ice is a chemical reaction that shows that oxygen isn't always a prerequisite for fire.
 
Materials
Bunsen or similar burner, chisel (or similar tool), thermal protection gloves, plastic spoon.

Chemicals
Magnesium turnings, magnesium pencil sharpener, two dry ice blocks.

Experimental

• Put on the thermal protection gloves.
• Work in a fume hood on a fire resistant surface.
• Use a chisel to make cavities in the center of the dry ice blocks. The size of the cavities should be at least 3 cm deep by 3 cm across. 
• Place magnesium pencil sharpener in the cavity of the dry ice block and add (with a spoon) magnesium turnings.
• Ignite the magnesium with flame of the burner and than cover it with the other dry ice block.
• The effect of burning (Fig. 1) is more vivid in the dark.
• Watch and wait till the end of the burning.
• After the end of the burning, remove the top dry ice block and show the product of the reaction.
• You can reuse the dry ice blocks.

Fig. 1. Burning magnesium in dry ice

Fig. 2. Product of the burning

Observation and Discussion

This experiment: Burning magnesium in dry ice is an example that oxygen isn't always a prerequisite for burning. The black substance (Fig. 2) which is a product of the burning is carbon:

2Mg + CO₂ → 2MgO + C

It is well known that carbon dioxide is used in some fire extinguishers but in case of burning magnesium these can not help.

Safety Tips
Dry ice blocks are very cold (melting point: −56.6 °C). Protect your hands with the thermal protection gloves. Use safety goggles. Work in a fume hood on a fire resistant surface. Some sparks can fly out of the blocks. To prevent this, use dry ice blocks that can close the cavity as good as possible (you need large flat surface).