Dissociation of Water Yajpor. 3 



spectrum tube speedily became milk white from the sodium 

 set free from the glass. 



Lord Rayleigh* has shown how to demonstrate the presence 

 of argon from very small quantities of air. My method is sub- 

 stantially his, except that I employ very powerful discharges 

 which set free a sufficient amount of sodium vapor from the 

 glass, and the oxygen is supplied from the dissociation of the 

 water vapor, which is always in evidence when such powerful 

 discharges are employed. The production of argon under 

 these circumstances is a striking proof that I am dealing in 

 this investigation with the spectrum of the dissociation of 

 water vapor. From the same tube one can, by modifying the 

 strength and character of the electrical discharges, obtain what 

 is termed the four-line spectrum of hydrogen, the spectrum of 

 sodium, the spectrum of argon, and the spectrum of the dis- 

 sociation of water vapor. Doubtless one could also recognize 

 the spectrum of helium ; I am not yet sufficiently familiar 

 with it. 



In the course of a study of the water vapor spectrum one is 

 naturally led to photograph the spectrum of the electric spark 

 under water. It is possible to obtain powerful discharges of 

 any suitable length under distilled water by enclosing the spark 

 terminals in glass tubes, allowing only a small portion of the 

 platinum terminals to project from the ends of the tubes. If 

 the terminals are immersed more than an inch under water, 

 the resulting explosion is apt to break the glass-containing 

 vessel. The light of these discharges under distilled water is 

 white and extraordinarily brilliant to the eye. When it is ex- 

 amined by the spectroscope one sees a continuous spectrum ; 

 and one obtains a continuous spectrum even by photography 

 in the most actinic portion of the spectrum. On bringing the 

 spark terminals to the surface of the water, leaving them barely 

 immersed, one immediately obtains the so called four-line spec- 

 trum of hydrogen. To what is due the continuous spectrum 

 under water? Does it result from the production of the water 

 vapor spectrum under great pressure? That there is great 

 pressure is shown by the sudden explosion, which is sufficient 

 to blow the small tamping of water out of both ends of the 

 containing tube. If the surface of the water is covered with 

 a thin film of oil, this oil is immediately disseminated through 

 the water, a milky white emulsion, which remains for days. 



When we turn to powerful discharges through Geissler or 

 Plucker tubes filled with hydrogen which has been dried with 

 great care, we also obtain a continuous spectrum on which are 

 supei'posed the bright lines of the water vapor spectrum, 

 together with certain reversed lines, giving on the positive 



*Phil. Mag. (6), vol. i, 1901, p. 103. 



