134 PHENOMENA, ATOMS, AND MOLECULES 



PRELIMINARY EXPERIMENTS WITH FLAMES OF 

 ATOMIC HYDROGEN 



To try out the possibility of blowing atomic hydrogen out of an arc, 

 20-ampere arcs from a constant-current transformer were passed between 

 two tungsten rods 6 mm. in diameter mounted transversely in a horizontal 

 alundum tube (lo cm. diameter) through which a stream of hydrogen 

 flowed. With voltages from 300 to 800, arcs could be maintained with 

 electrode separations up to 2 cm. The magnetic field of the arc caused it to 

 move transversely so that it became fan-shaped. Iron rods 2 or 3 mm. in 

 diameter melted within i or 2 seconds when they were held 3 to 5 cm. above 

 the arc. 



By directing a jet of hydrogen from a small tube into the arc, the atomic 

 hydrogen could be blown out of the arc and formed an intensely hot flame. 

 To maintain the arc in a stable condition the electrodes were brought close 

 together (i to 3 mm.), but the arc did not remain entirely between the 

 electrodes, but extended as a fan to a distance of 5 to 8 mm. The flame of 

 atomic hydrogen, however, extended far beyond the arc. At distances of 

 I or 2 cm. from the arc molybdenum (m. p. 2900° K.) melted with ease. 

 Near the end of the arc tungsten rods and even sheet tungsten (m. p. 

 3660° K.) could be melted. 



The use of hydrogen under these conditions for melting and welding 

 metals has proved to have many advantages. Iron can be melted without 

 contamination by carbon, oxygen, or nitrogen. Because of the powerful 

 reducing action of the atomic hydrogen, alloys containing chromium, 

 aluminum, silicon, or manganese can be melted without fluxes and without 

 surface oxidation. 



TEMPERATURE OF ATOMIC HYDROGEN FLAME COMPARED 



WITH OTHER FLAMES 



Let us suppose we could obtain atomic hydrogen in bulk at atmospheric 

 pressure and room temperature and that we could then let this "burn" to 

 the molecular form in a flame. What would be the temperature of this 

 flame and how would it compare with that of other flames ? Taking the heat 

 of reaction (for 2 grams) to be 98,000 calories and taking the specific heat 

 of molecular hydrogen (for 2 grams) to be 6.5 -f 0.0009 T, we find that 

 the heat of the reaction would be sufficient to heat the hydrogen to 9200° K. 



The dissociation of the hydrogen, however, would prevent the tem- 

 perature from rising to any such high value. If .r is the degree of dis- 

 sociation at the maximum temperature reached, the available heat of re- 

 combination is only {i — x) 98,000. 



The heat in calories, Q, needed to raise the temperature of a gram 



