The index of refraction for neutrons in ferromagnetic materials has been studied by total reflection from mirrors. It is shown that Bloch's constant, $C$, is unity; i.e., that the effective field for neutrons in a ferromagnet is B. For the case of total reflection, it is found that the magnetic part of the index is given by the field averaged over a region large compared to the size of the magnetic domains. Completely polarized thermal neutrons have been produced, without the necessity of monochromatization, by reflection from magnetized cobalt. Measurement of the polarization, performed by reflection at a second cobalt mirror, requires careful elimination of reorientation effects in the region between the mirrors.