• A Tantalus cup is a glass cup with a U-tube attached. When water reaches the top of the inverted U-tube, a siphon action begins which drains the water until the end of the U-tube is exposed. When the cup is filled with water, the water is forced up the inverted U-tube so that equilibrium is maintained in the cup. As the water level reaches the top of the U-tube it begins to fall through the siphon. As the water falls, it creates a vacuum which causes more water to be forced into the tube.
• Demonstrate to students how a siphon works
• Made from borosilicate glass

A Tantalus cup is a glass cup with a U-tube attached. When water reaches the top of the inverted U-tube, a siphon action begins which drains the water until the end of the U-tube is exposed. When the cup is filled with water, the water is forced up the inverted U-tube so that equilibrium is maintained in the cup. As the water level reaches the top of the U-tube it begins to fall through the siphon. As the water falls, it creates a vacuum which causes more water to be forced into the tube.