144 PHENOMENA, ATOMS, AND MOLECULES 



TABLE IV 



Maximum Temperatures of Metals Heated by Atomic Hydrogen Flame 



EvAPORA- Rate of Emis- 



Radiation tion Evaporation sivity 

 Watts per sq. cm. G./ cm./ cm. /sec. 



140 60 0.0095 0.36 



37 300 0.058 O.II 



Ag 2660 2740 20 330 0.125 0.07 



means of the emissivities given in the last column. The boiling points in 

 the third column were obtained from measurements of the rate of evapora- 

 tion from these metals in vacuum.^^ 



The rate of radiation of energy from the surface of the metal in watts 

 per square centimeter is given in the fourth column while the heat energy 

 corresponding to the cooling of the metal by its evaporation in the flame is 

 given in the fifth column. The observed rate of loss of weight in grams per 

 square centimeter per second is in the sixth column. It is clear that the 

 cooling by evaporation limits the temperature to which molten metals can 

 be heated except in the case of such difficult volatile metals as molybdenum 

 and tungsten. 



APPLICATION OF ATOMIC HYDROGEN FLAMES TO 

 ■ WELDING OF METALS 



The high temperature of this flame, together with its powerful chemical 

 reducing action and the avoidance of gases containing oxygen and nitrogen, 

 render it particularly useful for welding, not only for iron and its alloys, 

 but for such metals and alloys as contain aluminum, magnesium, chromium, 

 manganese, etc. 



Since a general account of these applications has already been pub- 

 lished,^^ only a brief summary will be given here. The technical develop- 

 ment of these processes is largely the work of R. A. Weinman. 



Figure 3 illustrates one of the later forms of torch used for welding. 

 Two tungsten rods, as electrodes, are held at a definite angle to one 

 another by easily adjustable clamps, and a jet of hydrogen is directed from 

 a small nozzle along each of these rods near its end. The hydrogen thus 

 bathes the heated parts of the electrodes and forms a gentle blast of gas 

 which passes through the arc between the electrode tips, and blows the 

 atomic hydrogen away from the electrodes so that these are not unduly 

 heated. Other torches have been built suitable for automatic welding using 

 machine feed. 



'* These data will soon be published by H. A. Jones and the writer in Phys. Rev. 

 ^^ Weinman and Langmuir, Gen. Elec. Rev., sg, 160 (1926). 



