IGNITION of the SAFETY MATCH RICHARD S. SIEGEL Brooklyn Technical High School, Brooklyn, New York
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HE usual explanation given in inorganic chemistry texts for the ignition of the safety match is the conversion of the red phosphorus on the striking surface to a vapor which then ignites. Some hooks go so far as to state that the vapor condenses to form white phosphorus which takes fire spontaneously. It is implied that the only function of the oxidizing agent is to keep the antimony trisulfide burning on the head of the match. It is also stated that lead dioxide, potassium chromate, potassium dichromate, or potassium nitrate may he used as the oxidizing agent instead of the potassium chlorate. Since it is well known that a mixture of red phosphorus and potassium chlorate will react with explosive violence if only little friction is applied, i t occurred'to the writer that it is the contact of the red phosphorus with the oxidizing agent which causes the primary ignition. In order to test this hypothesis, a number of match sticks were coated with each of the following mixtures:
potassium chlorate must he used.' The other oxidizing agents are added to prevent too rapid combustion of the head, which would be the case if potassium chlorate were used alone. The above idea makes it easier to explain why the entire striking surface does not go up in flames when a safety match is struck. The potassium chlorate, being a more powerful oxidizing agent than the atmosphere, causes the oxidation of the phosphorus to proceed a t a greater rate than if it were surrounded by air. The increased rate of oxidation will cause the phosphorus to burn a t a temperature much lower than its kindling point in air. The rest of the phosphorus on the striking surface, which is not in contact with an oxidizing agent other than air, will not burn a t the lower temperature. The Sb& in the match head burns because the original phosphorus-KC103 reaction produces a temperature high enough to kindle the mixture of trisultide and oxidizing agents in the head. .. To confirm this interpretation, the following experiments were ~erformed. A narrow strin of a mixture of A-glue, an abrasive (sand or carborundum powder) red phosph&s, KClOa, and glue wa5 painted on the striking surface of a safety match box. This was dried B-glue, an abrasive, and KClOa and then struck with a "match" made of glue and C-glue, an abrasive, and KNOa ' carborundum powder. The red phoSphorus-potassium chlorate strip took fire but the rest of the striking surD-glue, an abrasive, and K2Cr04 face remained unburnt, showing that the temperature E-glue, an abrasive, and K2Cr207 developed was not sufficient to ignite the red phosF-glue, an abrasive, and PbOz phorus on the striking surface. A mixture of SbSs, G g l u e , an abrasive, and NaCIOa KCIOs, and glue was then spread on a piece of roughened cardboard and allowed to dry. A strip similar to These matches were then struck on a safety match that painted on the safety match striking surface was striking surface. Series A, C, D,E, and F gave no then put on and dried. On being stmck with a carbodiscernible glow or spark even in a dark room. Series rundum powder "match," the KClOa-phosphorus mixBand G produced sparks visible in daylight. ture took fire and ignited the trisuhide-chlorate mixture If phosphorus vapor were formed upon striking the which in turn ignited the cardboard. To illustrate how match, it should condense a t some cool place on the low the ignition point of the potassium chlorate-phosstriking surface to form some white phosphorus which phorus mixture is, a sample of this mixture took fire would glow in the dark. Series A seems to prove fairly while drying in an oven a t 80°C. definitely that phosphorus vapor is not formed and that The experiments described in this paper bring the even if it is, it does not ignite. Series C, D, E, and F author to the conclusion that the usual explanation indicate that the oxidizing agents employed were not given for the ignition of the safety match is untenable energetic enough to cause the phosphorus to burn. and that it is erroneous to list oxidizing agents such as One is thus led to the conclusion that a chlorate is an K2CrOa,PhOz, etc., as substitutes for KC103. essential ingredient in any oxidizing mixture for the ,TheDiamond Co, of 30 Church St,, New York City, safety match. Since sodium chlorate is deliquescent was kind enough to confirm this conclusion.
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