Hand Boiler

A hand boiler or (less commonly) love meter is a glass sculpture used as an experimental tool to demonstrate vapour-liquid equilibrium, or as a collector's item to whimsically "measure love." It consists of a lower bulb containing a volatile liquid and a mixture of gases that is connected usually by a twisting glass tube that connects to an upper or "receiving" glass bulb.

In popular culture, hand boilers used to be sometimes known as "love meters" because the tube that separates the upper and lower bulbs is twisted into a heart shape and the volatile liquid is colored red. Love meters were a common collector's item or a souvenir. Depending on how the item was packaged, one would grasp the lower bulb to "prove" how passionate one was, or a couple would each grasp one end to see who would force the liquid into the other's bulb.

Hand boilers are much more commonly used as a scientific novelty today.