Henry Cavendish, London 1731 - 1810
1766 - Henry Cavendish, was a British scientist noted for his discovery of hydrogen or what he called "inflammable air".[1] He described the density of inflammable air, which formed water on combustion, in a 1766 paper "On Factitious Airs". Antoine Lavoisier later reproduced Cavendish's experiment and gave the element its name (hydrogen).
Martinus van Marum, Delft, Groningen, Haarlem, 1750 - 1837
1776 - Dutch scientist Martinus van Marum did various experiments with electricity. During one of his experiments (Groningen) he created Oxygen and Hydrogen gas using electrolises. He discovered (by accident?) that this mixture can be ignited (exploded) by an electric spark. No one got injured.
Antoine Laurent de Lavoisier, Paris 1743 – 1794
1781 - Antoine-Laurent de Lavoisier was a French nobleman prominent in the histories of chemistry, finance, biology, and economics. He stated the first version of the law of conservation of mass,[2] recognized and named oxygen (1778) and hydrogen (1783)

1789 - Dutch researchers Paets van Troostwijk and Joan Rudolph Deiman (Amsterdam) proved with their experiments for the first time, that water his elements are exactly 1 part oxygen and 2 parts hydrogen (exactly like what we now call Brown's gas / HHO gas). They used electricity to split water in his elements and used a spark to to combine the elements again in water. In the same experiment they were able to measure the exact volume of the elements.
1803 - Robert Hare developed and experimented with the oxy-hydrogen blowpipe
Drummond spot light
1826 - Thomas Drummond discovered that an intense illumination is created when an oxyhydrogen flame is directed at a cylinder of calcium oxide, which can be raised to white heat without melting. He built the so called "Drummond Light" also calles "Limelight". This "Drummond Light'' 'can be created with brown's gas and calcium oxide.

1875 - Jules Verne in his book The Mysterious Island, wrote the following age:
"Water decomposed into its primitive elements, and decomposed doubtless by electricity, which will then have become a powerful and manageable force. Yes, my friends, I believe that water will one day be employed as a fuel".
Henry Garrett, Dallas USA
1935 - Inventor Henry Garrett patented a electrolytic carburator and let a car run just on tap water.

1943 - 1945 - Because of serious conventional fuel shortage at the end of WW2, the British army used Brown's/ HHO Gas generators in their tanks, boats and other vehicles to get better mileage and to to prevent engine overheating for vehicles used in africa. They used generators like the today's HHO fuel savers. Right after the war all the generators were removed from the vehicles and destroyed.