Results of long slit optical spectroscopy of five radio galaxies 3C 31, 3C 75, 3C 83.1B (NGC 1265), 3C 405 (Sygnus A), and 3C 465, are presented. In most cases no extra-nuclear emission was detected. This makes it possible to set temperature and density limits for gas in the various volumes studied assuming equilibrium with the pressures implied by Einstein X-ray observations. These limits were obtained mainly from the H-alpha, Fe X (6374 A), and Fe XIV (5303 A) lines. These results rule out or set constraints on a number of models for the radio sources. Models involving cool deflecting clouds for bending 3C 465 and 3C 75, except with a very unlikely combination of parameters, are ruled out. It is also found that the data are inconsistent with heavy jet models for 3C 31. The temperature in the interstellar medium of NGC 1265 is found to exceed 3 x 10 to the 6th K and that the interstellar magnetic field must exceed 0.08 micro-G. It is also found that the large rotation measures seen in Cygnus A are probably produced in a foreground screen of hot gas rather than in a cool boundary layer between the radio source andmore » the intercluster medium. 43 refs.« less