The molal cryoscopic constant in molten pyridinium chloride (m.p. 146.0�) has been found to be 17.4� (subject to confirmation by calorimetry) and the cryoscopic heat of fusion, 2310�40 cal mole-1. In pyridinium chloride as a solvent, iodides appear to dissociate completely while bromides do not yield the expected depression possibly because of solid solution. Tetraalkylammonium and alkyl-pyridinium halides of high molecular weight are ideally dissociated in extremely dilute solution but with increasing concentration apparently form micelles.