FLAMES OF ATOMIC HYDROGEN 139 



heat that occurred before the maximum temperature was reached. This 

 correction rarely amounted to more than 5 per cent. 



The rate of surface heating in watts per square centimeter was then 

 calculated from the temperature rise, the time of application of the flame, 

 the area of the end of the tungsten tip (0.466 sq. cm.), the mass of copper 

 and its specific heat (0.394 watt second per gram per degree). A summary 

 of the results is given in Table II. Except where specifically noted, the 

 conditions for the use of each fiame were chosen to give the greatest 

 possible rate of surface heating. 



The rate at which heat is delivered to a tungsten surface by the atomic 

 hydrogen flame produced by a 60-ampere arc (1330 watts per sq. cm.) is 

 thus twenty-six times as great as that from a Bunsen burner flame and 

 about double that from the flame produced by the ordinary oxy-acetylene 

 welding torch. 



According to the Stefan-Boltzmann law the heat radiated from a body 

 at high temperature is 



Wit = ^-7 £ ( ■ I watts per sq. cm. ( 18) 



^^ \TOOO/ 



where E is the emissivity of the body (£ = i for a black body). 



If a Bunsen burner flame delivers 51 watts per sq; cm. to the whole 

 surface of a black body, it would thus heat it to 1730° K. If heat is applied 

 by the flame to one side of a plate-shaped body and the heat is radiated from 

 both sides, the temperature would be 1450° K. The fact that the Bunsen 

 flame does not heat bodies so hot as this indicates that the rate of surface 



Fig. 3. — One Form of Atomic Hydrogen Welding Torch. 



heating decreases as the temperature of the body increases. The heat 

 reaches the surface from such a flame by conduction through a relatively 

 stationary film of gas. The decrease in the temperature gradient when the 

 body becomes hot would explain the lower rate of surface heating. With 



