Step 1: Understanding the Concept:
Effervescent granules contain an acid (usually citric and tartaric acid) and a base (sodium bicarbonate). They must be prepared without adding extra water, which would start the effervescent reaction prematurely.
Step 2: Detailed Explanation:
1. Fusion Method: In this method, the powdered ingredients are mixed and heated in an oven at 34–40 \(^\circ\)C.
2. Citric Acid Monohydrate: Citric acid is used in its monohydrate form (\(C_6H_8O_7 \cdot H_2O\)). This molecule contains "water of crystallization."
3. Granulation: As the mixture is heated, the citric acid releases this bound water. The released water acts as a granulating agent, slightly moistening the mass just enough to allow it to be pressed through a sieve to form granules.
Step 3: Final Answer:
The internal water released from the citric acid monohydrate during heating provides the necessary moisture for granulation in the fusion method.