What is known as dead burnt?

Explanation

**Step-by-Step Solution:**

1. **Definition of Dead Burnt:**
- Dead burnt refers to anhydrous calcium sulfate (CaSO4).

2. **Characteristics of Dead Burnt:**
- It is also known as dead burned plaster because it does not set like plaster of Paris (POP).

3. **Comparison with Plaster of Paris:**
- Plaster of Paris is formed from gypsum (CaSO4·2H2O) when it is heated to about 120°C, resulting in CaSO4·1/2H2O.
- When gypsum is treated at higher temperatures (around 200°C), it loses more water and becomes anhydrous calcium sulfate (CaSO4), which is referred to as dead burnt plaster.

4. **Conclusion:**
- Thus, dead burnt is essentially anhydrous calcium sulfate, which does not undergo the setting process like plaster of Paris when mixed with water.

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