The chemistry of matches

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After fielding questions from students about what chemicals are in matches this week, it seemed like a good topic for a post looking at the question in more detail. When using matches on a day-to-day basis, you probably don’t think much of the chemical composition, or the reactions that are being set off; this graphic takes a look at some of the chemicals you can find in your average safety match, and the role they play.

Matches, as it turns out, have been around for a long time. Sulfur-based matches are mentioned as far back as the 1200s in texts of the time, and in the 1600s a process involving drawing sulfur matches through dried phosphorus-soaked paper was devised. However, the friction matches we’re used to have their origins in the 1800s; the first were developed by the English chemist, John Walker, in 1826. His matches involved a mixture of potassium chlorate, antimony (III) sulfide, gum and starch, which ignited when struck on sandpaper. These matches were somewhat unreliable in whether or not they would successfully strike, however.

In 1830, Charles Sauria, a French chemist, invented the first phosphorus-based match, by replacing the antimony sulfide in Walker’s matches with white phosphorus. Whilst much easier to ignite, these matches, too, had issues. Although they were manufactured over a number of decades, the toxicity of white phosphorus slowly became apparent. The long term exposure to white phosphorus of those making the matches led to ‘phossy jaw’ – an affliction which caused toothaches, major swelling of the gums, disfigurement, and eventual brain damage. The only treatment was the removal of the jaw bone. As more about the toxicity of white phosphorus became known, it was eventually banned in 1906.

Prior to the banning, alternatives had already been sought for use in matches. In 1845, Anton Schrötter von Kristelli discovered that heating white phosphorus, or exposing it to sunlight, turned it into another form of the element: red phosphorus. This form of the element is non-toxic; technically, it is not an allotrope, but rather an intermediate form between white phosphorus and another allotrope, violet phosphorus. Safety matches were subsequently introduced using red phosphorus in the place of white phosphorus.

So how do the safety matches of today function? The red phosphorus is, in fact, no longer found in the head of the match – rather, it’s located on the striking surface on the side of the box, mixed with an abrasive substance such as powdered glass. The match head contains an oxidising agent, commonly potassium chlorate, and glue to bind it to further abrasive materials and other additive compounds. These can include antimony (III) sulfide and/or sulfur, added as fuel to help the match head burn.

When the match is struck, a small amount of the red phosphorus on the striking surface is converted into white phosphorus, which then ignites. The heat from this ignites the potassium chlorate, and the match head bursts into flame. During manufacture, the match stick itself is soaked in ammonium phosphate, which prevents ‘afterglow’ once the flame has gone out, and paraffin, which ensures that it burns easily.

Unlike safety matches, ‘strike anywhere’ matches don’t require the red phosphorus striking surface in order to ignite. This is because they contain phosphorus in the match head, in the form of phosphorus sesquisulfide. Other than this difference, however, they still function in much the same way.

You can see the chemical reaction that occurs when a match is struck happening in super-slow motion in this amazing video by American cinematographer Alan Teitel (or with chemistry commentary from ACS Reactions here). If you want to find out more about the history of matches beyond this brief overview, check out the links below!

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