PARAFFIN OIL, a term widely used in the United King dom to connote burning oil or illuminating oil for use in lamps. The corresponding American expression is kerosene and this also is commonly used in the industry. Kerosene is the distillate from any crude mineral oil (including shale oil) that boils between the approximate limits of I so° C and 300° C. Legally it is defined as an oil that possesses a flash point above 73° F when observed in the standard Abel instrument. In early days paraffin oil was very liable to possess a low flash point and consequently many accidents occurred, owing to the fact that the oil gave off an inflammable vapour at moderate temperatures; to-day the flash point is usually above oo° F, because refiners are much more concerned with obtaining the maximum yield of petrol or gasolene from their crude oil, and therefore the illuminating oil coming on the market is practically free from low boiling, volatile and dangerous inflammable components. The chief criterion of a good illuminating oil is its capacity to burn with a steady highly luminous flame. This calls for great care throughout the refining operations.
The crude oil is first distilled in continuous stills arranged in benches and able to deal with upwards of •I,000 tons of oil a day. It is thus separated into naphtha and a heavy residue. This oper ation is called "topping" and the residue is a high flash oil that can be used as fuel or as a source of lubricating oil and waxes and pitch. The naphtha is redistilled and there is obtained from it a light petrol fraction and a heavier kerosene. In the most modern plant redistillation is avoided, the crude oil is pumped through a tubular still under pressure and discharged into a tall fractionating column that is provided with a series of perforated decks, the perforations being covered by serrated cast iron hemispherical caps. This arrangement brings about intimate con tact between the vapours ascending and the condensed liquid de scending. The vapour of the gasolene issues from the top of the
tower, which may be over 7o ft. high, whilst from a deck lower down the column may be taken kerosene. At various decks still lower down gas oil and lubricating oil are drawn and finally residue is taken from the bottom. The crude kerosene distillate thus ob tained although of correct flash point and boiling range, usually requires chemical treatments, to remove first colour and secondly objectionable compounds of sulphur that produce an unpleasant smell and poor burning qualities.
There is a variety of methods by which crude kerosene can be decolorised and deodorised. A widely used one is to agitate the crude oil with strong sulphuric acid, which dissolves out sulphur derivatives and the coloured impurities. If the mixture after thorough agitation is allowed to stand, there falls to the bottom of the agitator a heavy tar above which is the supernatant treated oil. The heavy tar is run off through a valve and the oil is washed several times with water, then with weak caustic soda and finally with water again. The oil thus purified is run to storage. This conventional method has many drawbacks and attempts are con stantly being made to improve upon it. Thus the Rumanian chem ist, Edeleanu, agitates the oil with liquid sulphur dioxide, thus sep arating from the oil by means of their greater solubility those bodies that cause inferior burning. The sulphur dioxide can be recovered and repeatedly used again. Other processes aim at removing objectionable materials by filtration through fuller's earth or ignited bauxite or other adsorptive materials, whilst again a common deodorising treatment is brought about by agitation with a solution of litharge in caustic soda. (A. E. D.)