LUBRICATING OILS. Mineral lubricating oils, belonging to the group of heavy distillates, they are used to reduce friction between working machine parts, engines and devices. They should meet the technical requirements, especially when it comes to viscosity, i.e. viscose, flash point and percentage of impurities that must not be exceeded. Lubricating oils used in the construction industry, distributed by CPN, are discussed below. Lubricating oils, as oil distillates, have to undergo a refining process. Refining is an oil purification process, as a result of which the oil acquires higher physical properties than the unrefined distillate. The refining is carried out at the factory by the acidic and selective method. Selective refining with solvents does not disturb the hydrocarbon particles, and only divides them into individual groups, Refined oil loses unnecessary hydrocarbons, which are absorbed by solvents, however, it gains the necessary paraffinic hydrocarbons. The chemical characteristics of lubricating oils are given by the following features: viscosity (viscose), oil viscosity curve, oil pour point, resistance to oxidation, flash-point, oil purity. In order to improve the degree of lubricity of Uników oils, admixtures of vegetable oils are used. The lubricity is the property of oil wetting metal surfaces, Polymerized castor oil is used for greasing mineral oils, vegetable oils mixed with mineral ones and treated with electric discharges, i.e. the so-called. volt oils and blown rapeseed oil. Regenerated oils are obtained by regenerating the oil after a certain period of engine operation, by removing the slurries and resin. The obligation to replace used oil with new one is regulated by special regulations and instructions.