Editing Percolation theory (section)

== History ==
The [[Flory–Stockmayer theory]] was the first theory investigating percolation processes.<ref>{{Cite book|url=https://books.google.com/books?id=Mw_csu3AcB0C&q=Flory%E2%80%93Stockmayer+theory+percolation+theory&pg=PA8|title=Applications Of Percolation Theory|last1=Sahini|first1=M.|last2=Sahimi|first2=M.|date=2003-07-13|publisher=CRC Press|isbn=978-0-203-22153-2|language=en|access-date=2020-10-27|archive-date=2023-02-04|archive-url=https://web.archive.org/web/20230204143734/https://books.google.com/books?id=Mw_csu3AcB0C&q=Flory%E2%80%93Stockmayer+theory+percolation+theory&pg=PA8|url-status=live}}</ref>

The history of the percolation model as we know it has its root in the coal industry. Since the industrial revolution, the economical importance of this source of energy fostered many scientific studies to understand its composition and optimize its use. During the 1930s and 1940s, the qualitative analysis by organic chemistry left more and more room to more quantitative studies. 
<ref>{{cite journal|last=van Krevelen|first=Dirk W|title=Development of coal research—a review. |journal=Fuel |volume=61|issue=9|year=1982|pages=786–790|doi=10.1016/0016-2361(82)90304-0 }}</ref>

In this context, the [[British Coal Utilisation Research Association]] (BCURA) was created in 1938. It was a research association funded by the coal mines owners. In 1942, [[Rosalind Franklin]], who then recently graduated in chemistry from the university of Cambridge, joined the BCURA. She started research on the density and porosity of coal. During the Second World War, coal was an important strategic resource. It was used as a source of energy, but also was the main constituent of gas masks.

Coal is a porous medium. To measure its 'real' density, one was to sink it in a liquid or a gas whose molecules are small enough to fill its microscopic pores. While trying to measure the density of coal using several gases (helium, methanol, hexane, benzene), and as she found different values depending on the gas used, Rosalind Franklin showed that the pores of coal are made of microstructures of various lengths that act as a microscopic sieve to discriminate the gases. She also discovered that the size of these structures depends on the temperature of carbonation during the coal production. With this research, she obtained a PhD degree and left the BCURA in 1946.
<ref>The rosalind franklin papers - the holes in coal: Research at BCURA and in Paris, 1942-1951. https://profiles.nlm.nih.gov/spotlight/kr/feature/coal {{Webarchive|url=https://web.archive.org/web/20220707220033/https://profiles.nlm.nih.gov/spotlight/kr/feature/coal |date=2022-07-07 }}. Accessed: 2022-01-17.</ref>

In the mid fifties, Simon Broadbent worked in the BCURA as a statistician. Among other interests, he studied the use of coal in gas masks. One question is to understand how a fluid can diffuse in the coal pores, modeled as a random maze of open or closed tunnels. In 1954, during a symposium on [[Monte Carlo method|Monte Carlo methods]], he asks questions to [[John Hammersley]] on the use of numerical methods to analyze this model.
<ref>{{Cite journal |first1=JM |last1=Hammersley | first2=DJA | last2=Welsh |title=Percolation theory and its ramifications.  |journal=Contemporary Physics |volume=21 | issue=6 |date=1980 |pages=593–605|doi=10.1080/00107518008210661 |bibcode=1980ConPh..21..593H }}</ref>

Broadbent and Hammersley introduced in their article of 1957 a mathematical model to model this phenomenon, that is percolation.