Brown's gas

Brown's gas (named for its inventor, Yull Brown) is a mixture of oxygen and hydrogen produced by electrolyzing water in a special way. Its proponents claim that it has unusual properties unlike those of an ordinary mixture of diatomic hydrogen and oxygen.

Claims
Among the many claims made about Brown's gas are:
 * It can be produced by electrolyzing water with no waste heat.
 * The volume of the gas is greater (almost twice as much) than would be expected from normal electrolysis.
 * It burns with a cold flame, yet somehow can be used to weld metals more efficiently than conventional fuels.
 * Under certain circumstances it implodes rather than explodes when ignited.

Theories
The most popular theory presented to explain these properties is that Brown's gas contains monatomic hydrogen and oxygen in significant proportions. This would explain the higher volume (the volume of a gas is proportional to the number of particles), but not some of the other claims. In particular, monatomic hydrogen and oxygen would burn with a hotter flame because the monatomic form has more energy than the normal diatomic form and this extra energy would be released as heat.

There are different explanations for how the monatomic gasses can exist at normal pressure instead of immediately combining (there is no activation energy because there are no bonds to be broken), none of which are fully satisfactory.

An alternative theory proposes that Brown's gas is really a hitherto unknown high-energy gaseous form of water, called "electrically expanded water".

Criticism
Skeptics point out that there is no solid evidence for any of these unusual properties, and suggest that all the observations could be explained by normal electrolysis and ordinary diatomic hydrogen and oxygen.