104 PHENOMENA, ATOMS, AND MOLECULES 



observations on the heat losses from tungsten filaments in hydrogen at 

 atmospheric pressure. In making squirted tungsten filaments, and some- 

 times in cleaning the drawn wire, filaments were heated in this manner in 

 hydrogen. Because tungsten filaments melt at a temperature more than 

 1500° higher than platinum, it had seemed to me that tungsten furnishes a 

 tool of particular value for the scientific study of phenomena in gases at 

 high temperatures. From my work on lamps I knew approximately the rela- 

 tion between the resistance of tungsten wire and its temperature, and could 

 thus use a tungsten wire as a kind of resistance thermometer. By connect- 

 ing a voltmeter and an ammeter to the tungsten filament which was being 

 heated in hydrogen, I could determine the temperature from the resistance 

 and also find the heat loss from the filament in watts. I wanted to see if 

 anything abnormal happened when the temperature was raised to the 

 extremes which were only possible with tungsten. 



The results greatly interested me, for they showed that the energy loss 

 through the gas, which increased in proportion to the square of the tem- 

 perature up to about 1800° K., increased at a much higher rate above that, 

 until at the highest temperatures the energy varied in proportion to about 

 the fifth power of the temperature. This result could be explained if the 

 hydrogen at high temperatures were dissociated into atoms. The diffusion 

 of the hydrogen atoms from the filament, and their recombination at a 

 distance from it, would cause an enormous increase in heat conduction. 

 After publishing these preliminary results, I was naturally much interested 

 in getting other information in regard to the properties of these hydrogen 

 atoms. A large number of experiments, extending over several years, 

 were thus made in this study of atomic hydrogen. Nearly all of these ex- 

 periments would have seemed quite useless, or even foolish, to a man who 

 was making a direct and logical attack on the problem of improving tung- 

 sten lamps. 



When nitrogen at low pressure was introduced into a bulb containing 

 a tungsten filament at extremely high temperatures, such as 2800° K., the 

 nitrogen disappeared at a rate which was independent of its pressure ; in 

 other words, here was a case of a reaction of zeroth order. This suggested 

 that the reaction velocity was limited by the rate at which the tungsten 

 evaporated from the filament. To check this hypothesis the rate of loss of 

 weight of filaments at various temperatures was measured in good vacuum. 

 This rate varied with the temperature in accordance with known thermo- 

 dynamic laws, and since the rate per unit area was independent of the size 

 of the filament, it was concluded that the loss of weight was really due to 

 evaporation and not to chemical action of residual gases or to electric 

 currents that passed from the filament to the surrounding space. 



A comparison of the rate of disappearance of nitrogen with the loss of 



