A ……..is a device used to measure heat.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a device that measures heat. The key term here is "measure heat," which indicates that we need to identify a specific instrument used for this purpose.

2. **Identifying the Device**: The device commonly used to measure heat is called a "Calorimeter." This instrument is specifically designed to measure the amount of heat absorbed or released during a chemical reaction or physical change.

3. **Function of a Calorimeter**: A calorimeter works based on the principle of heat transfer. When a substance undergoes a temperature change, the calorimeter measures this change to calculate the amount of heat involved.

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