Ignition of Gases by Hot Wires. 629 



The rates of absorption and adsorption of gases by metals 

 both vary with pressure, the former as the square root, the 

 latter as the cube root, and it might be expected that any 

 effect depending upon either would vary with pressure* 

 unless the rate of thermionic emission of gases once absorbed 

 were independent of it. 



One property of a gas that is independent of pressure is 

 its viscosity, and on Lodge and Clark's view of the origin 

 of the dust-free space around wires which are strongly 

 illuminated * it is at least possible that heat removed by 

 convection should be controlled by viscosity. On the other 

 hand, gases of such widely differing molecular properties as 

 hydrogen, ethylene, and carbon monoxide have the same 

 igniting currents. 



(2) Above Atmosjilieric. 



For the higher pressures glass apparatus was replaced by 

 the construction of fig. 9. A wrought-iron tube f inch bore 

 and 18 inches long, had at the upper end a cross-piece fitted 

 with a sparking-plug to which the wire was soldered, a quartz 

 window through which it could be observed, and an attach- 

 ment for a pressure-gauge and gas connexions. At the 

 lower end a "j"-piece had two ordinary water-taps fitted, one, 

 B, joined directly to the water main, the other, A, to drain 

 the pipe. At the start the three-way tap C is opened to 

 the atmosphere, A opened to drain the tube. The latter is 

 then closed and B opened, sweeping air or products of com- 

 bustion through C. The appearance of water here indicates 

 that the tube is full. B is then closed and C turned to the 

 gas supply, A opened and a measured quantity of water 

 drawn off, corresponding to the pressure required/the object 

 being to have at least 30 cubic centimetres of gas to explode. 

 A is then closed and B opened, admitting water and com- 

 pressing the gas. The pressure could be readily controlled 

 up to 100 pounds to the square inch, the highest pressure 

 of the mains. 



Explosions are heard as a faint click or can be seen through 

 the window. The cock on the gauge must be closed before 

 explosion. . 



The results with hydrogen and coal gas, the only gases to 

 be had at the time in large volumes, using platinum wire, 

 were as follows (Table V.). 



* "On the Phenomena exhibited by Dusty Air in the neighbourhood 

 of strongly Illuminated Bodies,'* 0. .1. Lodge and J. W. Clark. Phil. 

 Mag-. March 1884, p. 214. 



Phil. Mag. S. 6. Vol. 38. No. 227. Nov. 1910. 2 X 



