"In place of the oxygen which had thus disappeared, and a volume of hydrogen twice as great which had burned along with it, there was found a certain amount of liquid. The globe, moreover, had remained shut during the experiment, so that nothing had been allowed to escape, and nothing ponderable had been lost, for the vessel was found to weigh the same after the electric spark had passed, as before the explosion."
January 1, 1970
https://en.wikiquote.org/wiki/The_Life_of_the_Honble_Henry_Cavendish