LESSONS IN CHEMISTRY. 133 



the hydrogen flame just outside the dark center and the 

 liberated carbon passing through the hydrogen flame is heated 

 to incandescence, and just outside this hydrogen flame it com- 

 bines with the oxygen forming the dioxide of carbon. 



If air is admitted to the center of the flame, as in an Argand 

 burner, the dark center is lessened and the light increased. In 

 the case of the Bunsen burner air is allowed to mingle with the 

 gas so that the combustion is practically complete, yielding 

 a hot flame but very little light; for use in chemistry it is 

 better as it gives greater heat and leaves no deposit of soot. 

 The flame of alcohol yields but little light and deposits no 

 soot. Within certain limits the amount of light depends upon 

 the temperature of the flame. The temperature may be so low 

 as to hardly heat the carbon to incandescence when the light 

 must begin to fail. If by any means the temperature of the flame 

 falls below a certain limit it is extinguished. 



A piece of fine wire gauze held across the flame of a lamp or 

 candle cools the combustible gases below the ignition point so 

 that they rise through the gauze in the form of smoke, the gauze 

 may become red hot and still not allow the flame to pass, so 

 rapidly does the wire conduct the heat away, and yet the gases 

 may be ignited above the gauze. On this principle the miner's 

 safety lamp is constructed. Light carbureted hydrogen or marsh 

 gas, abundant in some coal mines, forms with air an explosive 

 mixture of great power, but the mixture must be raised to the 

 igniting temperature before explosion takes place. As the gas 

 is odorless often the first intimation of danger was the fatal explo- 

 sion of fire damp, lighted from the miner's open lamp. Sir Hum- 

 phrey Davy studied the problem, and at last made a lamp in 

 which the flame was surrounded by a wire gauze which so con- 

 fined it that the explosive gases outside could not be ignited. 

 As the gauze restricted the light it soon became the custom to 

 explore the mine for dangerous gas with a safety lamp and if 

 none was found the men wnt to work with open lamps. Aflame 

 seems a little thing, but the full discussion of a candle flame would 

 make quite a complete treatise on chemistry. 



