A sample consists of, at most, 100 mg of impure salicylic acid. A student adds 1 mL of hot water and a boiling stick and heats the resulting mixture on the sand bath. Not all of the solid dissolves so the student continues to add hot water dropwise. After another 0.5 mL of water has been added, for a total of 1.5 mL, there is still some white solid remaining. Provide an explanation and advise the student as to how to proceed.