How did Moissan isolate fluorine?
The isolation of fluorine required an extraordinary degree of patience and meticulous control of conditions. I knew that fluorine gas would attack almost any vessel, so I chose platinum-iridium alloy for its resistance. I then prepared anhydrous hydrogen fluoride by distilling it over potassium bifluoride to remove water. The key was to keep the electrolyte cold—below −50°C—using a bath of liquid ethylene, which slowed the corrosive action. I used a U-shaped platinum tube with platinum electrodes sealed in fluorspar stoppers. By passing a current, fluorine gas evolved at the anode. I confirmed its identity by its violent reaction with silicon and its ability to ignite charcoal. One must never trust a result that cannot be repeated, so I verified the process many times before publication.
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