Isobars for the adsorption of O 2 , H 2 and CO on evaporated films of Rh, Mo, W and Fe, of Ch and CO on Ta, Pt and Pd, and of O 2 on Cu, Al and Zn have been obtained. On Rh, Mo and W the rapid adsorption of O 2 and H 2 at -183° C results in formation of monolayers with one atom per surface atom. On Ta, Pt, Pd, Cu, Al and Zn oxygen, and on Fe hydrogen form similar monolayers, but on Fe oxygen forms several layers of oxide. On Rh, Mo and possibly Ta the fast CO chemisorption corresponds to a two-site mechanism; on W and Fe it lies between that for a single and a two-site mechanism; on Pt and Pd single-site adsorption may take place. Kinetics of slow oxygen uptakes have been followed on Rh, Mo, W, Ta, Fe, Cu and Zn. With Rh, Mo, W, Ta and Zn it is believed that formation of the first oxide layer has been observed, and the rate expression is velocity ∝√{ p ) e
-∝
v
/
RT , where v is the adsorbed volume and ∝ is a constant. The suggested mechanism is interchange of adsorbed oxygen atoms with underlying metal atoms, whereby metal atoms are exposed for further oxygen adsorption. On Cu and Fe formation of up to six and ten oxide layers respectively have been observed, and the rate expressions (u ∝ p0.75 / v2 and u ∝ p0.2e
∝'/
v ) have been interpreted in terms of the theory of Cabrera & Mott (1948).