Answer:
To avoid spattering
Step-by-step explanation:
If we are heating a hydrate to drive off the water of crystallization, we must initially heat the hydrate gently, at a lower temperature and then more strongly only after most of the water has been driven off in order to to prevent spattering.
Since we obtain the amount of water by the mass difference, Spattering decreases the mass of water obtained and ultimately results in a lower percent of water being calculated for the hydrate.