Two glasses of cold and warm water, as if without touching the glasses

Two glasses of cold and warm water, as if without touching the glasses, use a ballpoint pen to determine where is warm water and where is cold?

In order to determine where the water is cold and where it is hot, you need to lower the writing end of the crustacean into a glass of water and wait a little. If the water is warm, the ink level in the pen will start to rise. With an increase in temperature, the process of expansion of the black occurs, their volume will increase. In cold water, on the contrary, the volume of ink will decrease, since when the body cools down, its volume decreases.