from the Chandogya Upanishad #3

"Place this salt in water, and then wait on me in the morning." The son did as he was commanded.

The father said to him: "Bring me the salt, which you placed in the water last night."

The son having looked for it, found it not, for, of course, it was melted.

The father said: "Taste it from the surface of the water. How is it?"

The son replied: "It is salt."

"Taste it from the middle. How is it?"

The son replied: "It is salt."

"Taste it from the bottom. How is it?"

The son replied: "It is salt."

The father said: "Throw it away and then wait on me.”

He did so, but the salt exists forever.