This entry contributed by Dana Romero
A vessel filled with a transparent fluid that is on the verge of boiling, that is, under a pressure and a temperature for which it is on the liquid-gas boundary. For hydrogen this is only a few degrees above absolute zero, -273 Celsius. When an ionizing particle passes through a bubble chamber, it initiates a string of bubbles--due to boiling--along its path, which can then be photographed and analyzed.
