Answer:
He must be investigating its solubility in water.
Step-by-step explanation:
Solubility is the maximum amount of a substance that can be dissolved in 100mL or 100g of water at a given temperature.
So if a chemist dissolves some amount of a crystal in 100mL then it shows that is he investigating the solubility.
The rate of dissolution will be measured only if time is also noted.
To understand the reaction one has to do some other test after reaction.
To note the temperature change the chemist must use thermometer.