48 BURNING OR OXIDATION 



fire. Many destructive fires have been started by the ac- 

 cidental friction of such matches against rough surfaces. 



For these reasons the introduction of the so-called safety 

 match was an important event. When common phosphorus, 

 in the dangerous and easily ignited form, is heated in a closed 

 vessel to about 2 50 C, it gradually changes to a harmless 

 red mass. The red phosphorus is not only harmless, but it is 

 difficult to ignite, and, in order to be ignited by friction, must 

 be rubbed on a surface rich in oxygen. The head of a safety 

 match is coated with a mixture of glue and oxygen-contain- 

 ing compounds ; the surface on which the match is to be 

 rubbed is coated with a mixture of red phosphorus and glue, 

 to which finely powdered glass is sometimes added in order 

 to increase the friction. Unless the head of the match is 

 rubbed on the prepared phosphorus coating, ignition does not 

 occur, and accidental fires are avoided. 



Various kinds of safety matches have been manufactured 

 in the last few years, but they are somewhat more expensive 

 than the ordinary form, and hence manufacturers are reluctant 

 to substitute them for the cheaper matches. Some foreign 

 countries, such as Switzerland, prohibit the sale of the 

 dangerous type, and it is hoped that the United States will 

 soon follow the lead of these countries in demanding the sale 

 of safety matches only. 



39. Some Unfamiliar Forms of Burning. While most of 

 us think of burning as a process in which flames and smoke 

 occur, there are in reality many modes of burning accom- 

 panied by neither flame nor smoke. Iron, for example, 

 burns when it rusts, because it slowly combines with the 

 oxygen of the air and is transformed into new substances. 

 When the air is dry, iron does not unite with oxygen, but 

 when moisture is present in the air, the iron unites with the 

 oxygen and turns into iron rust. The burning is slow and un- 



