The crude oil is delivered at the refinery into large tanks, which are placed at a sufficient height to feed the stills by gravitation. The crude oil is allowed to settle for twelve or more hours at a temperature sufficiently high to separate any water that may have passed the test at the retorts, and after this water has been run off, the oil is fed into the centre boiler of a battery of oil boilers. The lightest fraction of the oil--ultimately motor spirit and illuminating oils--is distilled off the feeding boiler and condensed in a coil of cast-iron pipes immersed in water in a tank, cold water being continuously run into the tank, while heated water is run off. The boilers on each side of the feed vessel receive their oil by a pipe connecting with the bottom of the latter, and they also distil over the lighter portion of oil with which they have been fed, the heavier portions passing on to a third boiler, where the process of distillation is repeated. The oil now left is delivered into a cast-iron pot-still, in which it is ultimately distilled to dryness, the residue left in the still forming oil coke, which is valuable as a fuel on account of its high percentage of fixed carbon and low yield of ash. Steam is admitted to the still in large quantities at all distillations. The various stages of distillation are carried through in almost identically the same manner as that of crude oil, and, therefore, need not be described in detail. The treatment or washing of the oil to remove the impurities that cannot be eliminated by distillation, consists in stirring the oil by compressed air for a given time in an iron vessel, with a fixed quantity of sulphuric acid, allowing it to settle, and running off the heavy mixture of tar and acid which separates. The acid-treated oil is then run into another similar vessel, treated with a solution of caustic soda, settles, and the soda tar which separates is run off. The acid tars are steamed and washed, the resulting acid water being sent to the sulphate of ammonia house for the manufacture of sulphate of ammonia, whilst the tar is mixed with that from the soda treatments and burned under the stills as liquid oil. As there is more than sufficient of this tar to distil all the oil at the various stages, the distillation is carried out without cost for fuel, excepting that necessary for steam-raising purposes.