Hand Boilers are glass sculptures containing a liquid that will boil as heat is transferred from your bare hand. Simply hold the large bulb end on the bottom in the palm of your hand and within minutes, your body heat from your hand will cause the liquid to rise. Once out of your hands, it takes a few minutes for the liquid to cool down. Pretty fascinating science toy and an excellent demonstration of energy transfer. Havens treasure: - Romantic Heart Love Meter Hand Boiler Love Tester Special Gift for Your Lover Valentine Gifts Love Meter, Love Tester - Valentine Special Gift Love Meter, Love Tester: Valentine Gift Love Meter Energy Transfer Hand Boiler- Valentine Special Gift | Valentine Gift for Him, Valentine Gift for Her, Valentine Gift for Boyfriend, Valentine Gift for Girlfriend, Valentine Gift for Husband, Valentine Gift for Wife. Please Note: Manual measurement, please allow a slight error in size. There may be slight differences in colors due to different screens.