UNFAMILIAR FORMS OF BURNING 53 



match was an important event. When common phosphorus, 

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

 vessel to about 250 C., it gradually changes to a harmless red 

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

 cult 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-containing com- 

 pounds ; 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 manufacturers are reluctant to 

 substitute them for the cheaper matches. Some foreign coun- 

 tries, 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 requiring the sale of safety matches only. 



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 accompanied by neither flame 

 nor smoke. Iron might be said to burn when it rusts, because 

 it slowly combines with the oxygen of the air and new sub- 

 stances are formed When the air is dry, iron does not unite 

 with oxygen, but when moisture is present, the iron unites with 

 the oxygen and turns into iron rust. The burning is slow and 

 unaccompanied by the fire and smoke so familiar to us, but 

 the process is none the less burning, or combination with oxy- 

 gen. Burning which is not accompanied by any of the ap- 

 pearances of ordinary burning is known as oxidation. 



The tendency of iron to rust lessens its efficiency and value, 



