In order to encourage the more economical use of oil in industry many interesting and to a certain degree efficient devices have been introduced. But for the most part these apparatus are devoted to the filtering of what may be described as dirty free oil. They scarcely venture beyond the removal of whatever impurities may be associated with the product in the suspensory form. They do not attempt to reclaim waste oil. Such timid treatment is readily explicable. Oil is a somewhat sensitive product. Its inherent qualities may be easily impaired. For example, oil prepared essentially for lubricating purposes must be possessed of specific qualities, of which viscosity is one and the most important. Then the requirements of lubricating oil fluctuate so widely. An oil designed for use with a high-speed engine, such as the petrol motor, is not adapted to the lubrication of a slow-moving steam engine. Yet the depreciation of one single quality in any one grade is adequate to render the oil unsuited to the purpose for which it has been specially prepared. The consumption of lubricating oil by the authorities during the war ran into imposing figures, and the liability to waste was proportionate to the consumption. Aeroplane engines and lorry motors, together with their auxiliary gearing, were in a constant condition of overhaul. Every time an engine or gearbox had to be dismantled many gallons of oil had to be drawn off. Consequently the handling of this enormous quantity of material to frustrate waste demanded special consideration, inasmuch as the oil could not be put back into the machinery after the latter had been reassembled. The authorities solved the problem by the perfection of an organization for the collection of this oil, which was returned to the oil-refinery to be re-conditioned, that is to be cleaned thoroughly and to have its original properties restored. By the observance of this practice of turning old oil into new the country was saved huge sums.