PETROLEUM 719 commences at a very low temperature and proceeds at a constantly rising temperature, the distillate steadily increasing in specific gravity. The last portions distil at nearly a red heat, arid are nearly solid at ordinary temperatures, with a specific gravity above 900. The oil is first allowed to settle in large tanks, when about 1 per cent, of water and sediment is removed. It is then pumped to stills into which "live" steam is introduced. Distillation com mences at once and is allowed to proceed until the specific gravity of the distillate reaches 74 (60 B). The oil in this condition is called "gas-oil," and is used to a limited extent in the manu facture of illuminating gas. The distillate is crude naphtha, and is redistilled and divided into (1) rhigolene or cymogene, having a specific gravity of 62 and boiling at 65 a Fahr. ; (2) gasolene, specific gravity 66 (90 to 80 P>.) ; (3) C naphtha, specific gravity 70 (80 to 68 B.) ; (4) B naphtha, specific gravity 72 (68 to 64 B.) ; and (5) A naphtha, specific gravity 74 (64 to 60 B.). Below 60 goes to illuminating oil. The crude oil from which the naphtha has been removed is then put into a suitable still and distilled until the distillate has a specific gravity of 81 (40 B.). This distillate is crude illuminating oil. The oil remaining in the still may then be "cracked" by destructive distillation, or may be distilled for lubricating oil. If it is to be "cracked" the fires are slacked and the distillation allowed to proceed slowly, in consequence of which the vapours of the heavy oil are repeatedly condensed upon the dome of the still and made to fall back upon the hot oil beneath. The result is the production of a large volume of permanent gas, chiefly marsh gas and hydrogen, a distillate of suitable specific gravity for illuminating oil, and a heavy tarry residue, called "residuum," that remains in the still. By this method of manipulation the crude oil is converted into crude naphtha, crude illuminating oil, and residuum, while the gas is burned as a waste product. The residuum is run out of the .still and sold to manufacturers of lubricating oil. If the oil is not to be cracked, the heavy oil, from which the illuminating oil and naphtha have been removed, is often distilled with superheated steam and treated for lubricating oil. If simply distilled and treated with chemicals after removal of the paraffin, the oil is called in the United States "paraffin oil." The crude paraffin oil is placed in barrels in an ice-house, and, after it has been several days at rest, paraffin crystallizes from it. The paraffin is removed by pressure, and may be purified by any of the methods described under PARAFFIN (p. 242 above). The oil from which the paraffin has been pressed may be subjected to a further distillation in a .steam -coil or other suitable still, and deprived of certain oils that boil at a high temperature but have a pungent and offensive odour. When drawn off, the oil remaining iu the still is found to be light-coloured and nearly tasteless and odourless. It is called "deodorized neutral heavy hydrocarbon oil," and is found to be a very valuable lubricating oil. Th distillate above mentioned after treatment is called "mineral sp^rm," and is used as an illu minating oil on cars and steamboats, where a more volatile oil would be objectionable. Any of these distillates, from gasolene to the most dense lubricating oil, may be purified by filtration or by treatment with acids and alkalis. Filtration is usually applied to the different grades of naphtha to deprive them of disagreeable odour, for which purpose gravel and both wood and animal char coal are used, either separately or together. Lubricating oils are often filtered through animal charcoal to deprive them of both colour and odour. The dense vacuum residues recently prepared under the name of cosmoline, vaseline, &c., are filtered through animal charcoal while hot and perfectly fluid. Oils are treated with chemicals in high cylindrical tanks of small diameter, where they are thoroughly mingled by means of air forced into the bottom of the tank under pressure. These agitators often hold 50,000 gallons. The illuminating oils are usually treated with 5 per cent, of oil of vitriol at a temperature of about 60 Fahr. The acid " sludge," consisting of the oil of vitriol combined with the impuri ties of the oil and forming a black tarry liquid, settles to the bottom of the tank and is drawn off. The oil is then agitated with water, then treated with a solution of caustic soda, and finally washed with water containing caustic ammonia. Hydrochloric acid is used to a limited extent, and nitric and chromic acids are used to destroy fluorescence in dense oils. Those illuminating oils especially that are prepared by cracking are thrown after treatment, and while warm, in a thin spray into a large tank. This causes a small amount of very volatile oil produced by cracking to be evaporated, and brings the oil up to test. Finally the oil is exposed under a skylight in large shallow tanks until it has become perfectly clear from settling of all impurities. The acid " sludge " is for the most part sold to manufacturers of commercial fertilizers or restored by evaporation and used over again. More than 45,000 tons of oil of vitriol were used in 1880 by the manufacturers of petroleum in the United States. The alkali sludge is thrown away. The following table shows the average percentage of commercial pro ducts obtained from crude petroleum of 79 (45 B.) from Pennsyl vania, Ohio, &c. Per cent. Gasolene i to 1} " C " naphtha 10 "B" naphtha 21 "A" naphtha 2 to 2j 16} Illuminating oil 50 to 54 Lubricating oil 17} Paraffin vax=4} Ib per barrel 2 Loss 10 If the oil is "cracked," the yield is Naphthas Illuminating oil Residuum . Loss 100 16} 70 2 Lubricating Oils. Crude petroleum and the heavy distillates from petroleum, finished either by treatment or by filtration, have been slowly winning their way with consumers of lubricating oils for the last twenty years, and may now be said to have a recognized value. This result has been due as much to improved processes of manufacture, and consequently to improved quality of the pro ducts, as to a recognition of their merits. When properly prepared, and exempt from volatile matter and offensive odour, they are found to be possessed of great endurance, to be free from a tendency to gum, and to be incapable of spontaneous combustion. When mixed with animal and vegetable oils liable to spontaneous combustion, these oils prevent it. They are therefore now in large demand, a demand which is likely to increase as new applications are found for them and their quality is improved. Illuminating Oils. Oils of this class manufactured from petro leum have nearly superseded the use of other illuminating fluids throughout the world. They are largely sold in Great Britain under the name of "paraffin oils" ; in the United States they are called "kerosene," and on the European continent "refined petroleum." The different qualities are known as " water white, " "standard," and "prime," and are further distinguished as "low test" and " high test " oils. The characters chiefly relied on in the trade are "colour" and "test." The colour should be as light and free from opalescence as possible. Colour is, however, a matter of little importance except as it indicates unskilful manufacture of the oil. The " test " is of paramount importance, and indicates the tempera ture Fahr. at which the oil will give off a sufficient amount of vapour to ignite explosively when the oil is properly tested. While the methods of testing petroleum vary greatly, the apparatuses used for that purpose may be divided into three classes. The first class is designed to ascertain the tension of the vapour given off by a given sample at a certain fixed temperature ; these are chiefly used in France. The others are designed to show at what temperature a given amount of oil, usually half a pint, will give off a sufficient amount of vapour to form an explosive mixture with the air above the oil. These are divided into "open testers," in which the oil is heated in an open vessel, and "closed testers," in which the oil is heatod in a closed vessel. The tester invented by Sir F. A. Abel (see PARAFFIN, p. 239) has been adopted in Great Britain and her colonies, while in the United States and on the Continent a great variety are in use. The numerous accidents, many of a frightful nature, and involving great loss of property and often of human life, that have followed the use of illuminating oils which had not been properly freed from the volatile products of the petroleum, have led in most European countries and many of the American States to the enact ment of stringent laws forbidding the sale or use of oils the test of which does not come within the prescribed legal limits. Very valu able researches on the flashing of oils have been made by Dr C. F. Chandler of New York, and by other American chemists. Dr Chand ler showed that oils burning in lamps of ordinary construction in a room the temperature of which was below 90 Fahr. failed to reach an average temperature of 100 Fahr. In metal lamps, particularly "student lamps," the average temperature was several degrees higher than in glass lamps, a fact which shows glass lamps to be safest in this respect. Dr C. B. White of New Orleans has examined illu minating oils with respect to the amount of volatile material that, when added to good oil, will render it dangerous. He found that from 1 to 5 per cent, of the ordinary naphthas of commerce would render illuminating oil of the best quality extremely danger ous. Five per cent, of crude naphtha reduced the flashing point from 118 to 70 Fahr. These researches have all demonstrated the wisdom of English legislation on this subject, but unfortunately have not been productive of equally good results in the United States. Petroleum legislation is there in a very unsatisfactory con dition. The very worthless law passed by Congress in 1867 has long been repealed, and no other has been substituted for it. A number of the States (seventeen in 1880) are without legislation in reference to this subject, while legislation in other States is based upon local influence rather than fixed principles, and ranges in its
