OXYGEN AND OZONE. 57 



59. Combustion of Steel in Oxygen. Some things which 

 will not burn at all in common air will do so in oxygen 

 gas. This is the case with even so hard a substance as 

 steel. Take an iron wire, or, better, a steel watch-spring, 

 which you can get at any jeweler's, melt a little sulphur and 

 drop it on one end of the spring, ignite the 



sulphur, and introduce it into the oxygen in 

 the manner represented in. Fig. 10. The com- 

 bustion will at once be communicated to the 

 wire, and it will go on, throwing off sparks of 

 intense brightness till most of the oxygen is 

 united with the iron. The experiment will 

 be very brilliant if the steel spring be coiled. Fig< 10 * 

 The result of the combustion in this case is a solid, for the 

 oxygen unites with the iron to form an oxide of iron. The 

 sparks which fly from the red-hot iron struck by the black- 

 smith's hammer are the same, being formed by the union 

 of the oxygen of the air with some of the iron. But there 

 is this difference : The sparks emitted from the iron in the 

 oxygen are much hotter, because the combustion is more 

 brisk and perfect. Some of the iron falls in small burning 

 globules, which are so intensely hot as to be imbedded in the 

 glass, or they may even go through it if it be thin. We have 

 spoken of iron as not burning at all in air. This is not 

 strictly true, for every time that we strike fire with a steel 

 and flint, or with the heel of the shoe upon the sidewalk, we 

 set fire to a particle of steel. It is not only an exceedingly 

 little fire, but it is also momentary. It would be continuous 

 if the air were all oxygen, and the shoes on our feet would 

 be constantly taking fire from this cause. 



60. Oxygen Essential to Life. As ordinary combustion 

 can not go on without oxygen, so also is its presence essen- 

 tial to the continuance of life. It is the oxygen of the air 

 that supports life in all breathing animals, and no other gas 



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