Abstract In the foregoing paper methods have been described for studying the adsorption of hydrogen on tungsten. Similar experiments have been carried out with oxygen. It is known from thermionic work that oxygen forms an adsorbed film on tungsten which is stable up to nearly 2000° K. The present experiments show that on top of this a second film is formed which is quite stable at ordinary temperatures. The properties of both films have been investigated. 1—Accommodation Coefficient of Neon We shall first consider the results obtained, using the accommodation coefficient of neon as an indicator. The experiment was carried out in the same way as with hydrogen except that the oxygen (prepared by heating potassium permanganate) was introduced into the stream of neon at such a place that it did not to pass through a charcoal tube before reaching the tube containing the wire. It was rapidly removed from the neon by the charcoal, and several admissions were necessary before the accommodation reached the saturation value.