The most important method of preserving perishable materials is by refrigeration. Refrigeration generally means the removal of heat from a body or substance to such an extent as to leave it, or maintain it, at a lower temperature than that of the surroundings. Mechanical refrigeration refers to the removal of heat by mechanical devices. In mechanical refrigeration cycles a large variety of refrigerants, such as ammonia, sulfur dioxide, methyl chloride, freon-12 (dichlorodifluoromethane), and propane are used. These refrigerants must have properties that render them suitable for use in refrigeration cycles. During the refrigeration cycle, the refrigerant is constantly changing state; that is, from a liquid to a gas and vice versa with a corresponding change in temperature. One of the fundamental properties affecting the mechanical behavior of a refrigerant is its viscosity. Not only is it the major factor in relation to the transfer of the material, but it also has marked effect on the heat transfer characteristics of the refrigerant. Inasmuch as the refrigeration cycle depends on both of these operations, a knowledge of the viscosity of the refrigerant is highly desirable. It was the purpose of this investigation to determine the liquid viscosities of an azeotropic of asymmetrical difluoromethane and dichlorodifluoromethane. / Master of Science