The emission of short wavelength visible light from argon-hydrogen mixtures irradiated by a pulsed 1.7 MeV electron beam has been studied, as well as the absorption of 4416A radiation in the mixture. Absorption was found to increase faster than linearly with increased argon pressure. A new multipass gain or absorption measuring technique was devised which measures small amounts of gain with high sensitivity. At the highest excited state density obtained, 3 x 10 to the 13th power /cc, the absorption in argon-hydrogen mixtures is positive.