Today In Science History – September 28 – Henri Moissan

Henri Moissan

Henri Moissan (1852-1907) French chemist. Credit: Nobel Foundation

September 28 is Henri Moissan’s birthday. Moissan was the French chemist who was the first to successfully isolate the element fluorine.

Isolating fluorine was a goal for many chemists throughout the 19th Century. It was known to be an element back in the late 18th century, but no one had successfully found a way to isolate it from other compounds. Fluorine is a highly reactive substance and was prone to violent reactions that could blind, maim or kill would-be discoverers. Fluorine gained a reputation of the “chemist killer” after several deaths involving people trying to separate fluorine from hydrofluoric acid.

Moissan was attracted to the fluorine problem and set out to find a way to accomplish it. He began experimenting with electrolysis of hydrofluoric acid salts in a similar method pioneered by Humphrey Davy. After several failures, Moisson decided to try lowering the temperature of his hydrofluoric acid before electrolysis. When he lowered the temperature to -50ºC, the anode on his machine began to produce a yellow gas that would ignite when silicon and boron powders were added to it. He had produced the first samples of pure fluorine on June 26, 1886.

Moissan would continue to explore the chemistry of fluorine now that he had a steady source of the gas. One side effect of this research was the development of the electric arc furnace that bears his name. The electric arc furnace is a device that generates extremely high temperatures using high current across two nearly touching electrodes. These electrical arcs can heat their surroundings to a few thousand degrees in a very short amount of time. Moisson used his furnace to produce many exotic metals such as chromium, vanadium, uranium, tungsten and molybdenum. The project that attracted his attention the most from this device was trying to synthesize diamonds.

Diamonds are formed from carbon under high temperature and pressure. Moisson believed he had the necessary means to generate enough temperature and began trying different methods of generating high pressure at the same time. His best results came from heating a mixture of charcoal and iron until it was a glowing molten mass. He then dropped it into cold water. The quick cooling would suddenly condense the mass and generate high pressure. When he broke open the cool solid, he found small clear crystals of high density and hardness. Moissan would go to his grave believing he had successfully produced synthetic diamonds. He actually produced silicon carbide.

Moisson would be awarded the 1906 Nobel Prize in Chemistry for the isolation of fluorine and subsequent works involving the element and for his development of his electric arc furnace.

About Todd Helmenstine

Todd Helmenstine is the physicist/mathematician who creates most of the images and PDF files found on Nearly all of the graphics are created in Adobe Illustrator, Fireworks and Photoshop. Todd also writes many of the example problems and general news articles found on the site.