For all purposes, where lubricating properties and viscosity at somewhat elevated temperatures are required, the natural vaseline is preferable to the artificial, but the reverse appears to be the case where fluidity at a moderate temperature is desired, and where an appreciable tendency to acidification is prejudicial. The possibility of obtaining anthracene and other aromatic bodies from petroleum and petroleum residues, has already been dwelt upon in the section relating to the chemistry of petroleum. It is well known that the action of heat greatly alters the chemical composition of petroleum hydrocarbons, and that at a red heat, more or less anthracene and naphthalene are produced, together with other dense hydrocarbons, with an accompanying formation of coke and permanent gas. The preparation of anthracene, &c., from petroleum residuum, is not yet practised on a commercial scale, although successful experiments have been carried out by Nobel Brothers and others. According to Dr. Veith, Professor Letny was the first to produce (in 1877) aromatic bodies from petroleum. Shortly after this, Liebermann and Burg2 and Wichelhaus and Salzmann3 investigated the matter, employing petroleum residues in their experiments. It has been found that if the residues are slowly passed through iron tubes heated to 700° to 800° C., the products consist of 40 to 50 per cent. of tar, and 50 to 60 per cent. of gas, but little coking taking place under ordinary circumstances. When the decomposition occurs at a proper temperature and in presence of a good heat conductor, the yield of tar and aromatic bodies is increased. It appears that copper turnings placed in the tube are useful for this purpose. The specific gravity of the tar varies from 0.995 to 1027, according to the temperature at which the dissociation is effected, and the speed of passage through the heated pipes. On the average, the tar yields 17 per cent. of benzene, 0.4 per cent. of anthracene, and 7 per cent. of naphthalene. Roughly speaking, a slower rate of passage through the pipes produces a greater yield of tar, and an increased proportion of benzene and anthracene. According to Lermontowa, who obtained as much as 20 to 22 per cent. of benzene, and 0.8 of anthracene from the tar, a good tar of specific gravity 0-994 to 1·008 yielded : Up to 140° C., 36 per cent. of distillate. 200° C., 8 per cent. of distillate, which congealed from the 260° C., 15.5 per cent. 300° C., 4.7 per cent. The methods adopted in the separation from crude petroleum of various commercial products, and their purification by chemical treatment, have thus far been described in more or less general terms; but it is now necessary to refer specifically to processes which are peculiar to the countries where the manufacture is principally conducted. As some descriptions of crude petroleum yield but a very small proportion of solid hydrocarbons, the separation and refining of paraffin has not been described in the foregoing general account. 1 Dingler's polytech. Journ., ccxxix., 353. 2 Berichte d. d. Chem. Gesell., xi., 723. 3 Ibid., xi., 802 and 1431. THE REFINING OF PETROLEUM IN THE UNITED STATES. The oils of Pennsylvania and New York are collected by the pipeline companies in groups known as Bradford, Middle District, and Washington crude oils, but otherwise they are mixed indiscriminately in the companies' reservoirs. The refining of petroleum in the United States is principally conducted by the Standard Oil Company, who own a considerable number of refineries. The crude oil is delivered at the refineries into storage tanks of a capacity varying from 10,000 to 36,000 barrels, from the pipe-lines or tank cars. From the tank cars, the oil is usually first run into a receiving tank, through a 12-inch pipe laid between the rails, and furnished with suitable unions, by means of which the con Fig. 118. tents of all the tank cars of a train may be discharged simultaneously, and from it the oil is pumped into the storage tanks. In his report on the Production, Technology, &c., of Petroleum, Professor Peckham has described the successive operations carried on in the large refineries in the United States. In some of these, only naphtha, illuminating oils, and residuum are produced, and in others the operations are confined to the distillation of the residuum for the production of lubricating oils, paraffin, &c., while in a few, both sets of products are manufactured. The following description applies to a refinery where naphtha, illuminating oils, and residuum are produced. The battery of stills comprises three of the cheese-box type (see p. 312) and six plain cylinder stills (see p. 312), 30 feet long by 12 feet 6 inches high, the former being set in one group and the latter side by side in a bench. All have sheet-iron jackets, but are otherwise uncovered. The condenser is of the parallel-tube type (see p. 329), and the tank measures 50 feet x 20 feet x 8 feet. The vapour pipes from the various stills are brought together side by side before connection with the condenser, which is common to them all. Each vapour pipe terminates in a U-shaped gas trap (Fig. 118), which allows the liquid portion of the distillate to flow through, but checks the gas so that it passes through a pipe, b, whence it is allowed to escape, or is more commonly passed into the furnace and burned after admixture with air. The distillates from the nine stills pass into nine boxes (Fig. 119), each fitted with a glass door, a, so that the distillation may be watched and samples may be taken, and each discharging into a set of pipes, 1 to 5, having taps arranged as shown, so that the distillates may be run into any one of five or six underground tanks. The crude naphtha, and that portion of the oil from which high-test oils of 120° to 150° F. fire test are prepared, are first distilled off, and the fires being then slackened, the "cracking" of the residual oil commences, with disengagement of an amount of gas enormously exceeding that produced during the earlier stages of distillation. The collection of the naphtha is usually continued until the density of the distillate rises to about 62° B. (specific gravity 0·731), the stream being then diverted to the kerosene tank if an oil of 110° to 120° fire test is required; but when an oil of 150° fire test is being made, the collection of kerosene is not commenced until the density of the distillate reaches about 56° B. (specific gravity 0·754). In some cases, the naphtha which distils off at a density between 70° B. (specific gravity 0702) and 62° B., is separately collected, and the more volatile portion of it afterwards driven off in a still by steam heat, so that the remainder may be added to the kerosene. When, however, the higher test oil is required, the distillate, which has a density ranging between 62° B. and 56° B., is added to the lower test oil, and the distillation for kerosene is continued until, in the case of ordinary oil, the specific gravity of the product slightly exceeds 0.800, or in the case of higher test or water-white oil, until it is about 0.790. Although the quantity of naphtha and kerosene obtained varies largely according to the nature of the crude oil, the average yield of crude naphtha has been stated to be about 12 per cent., and of kerosene about 75 per cent. of 110° fire test. The amount of water-white kero sene obtainable is said to vary from 12 to 20 per cent., with a corresponding reduction in the yield of ordinary kerosene. The fluid residue in the still amounts to about 6 or 7 per cent. of the crude oil, and is run off for treatment as hereafter described, the coke, which represents from 1 to 1 per cent., being removed from the still by hand. According to Mr. Folger1 it is now the usual practice to fractionate the distillate into light and heavy naphtha and two grades of burning oil, the lines of demarcation being, of course, purely arbitrary. The densities of the naphtha range from 90° to 62°, and of the refined oil distillates from 50° to 44°, the density of the residuum being from 25° to 16° B. The separation thus effected is imperfect, the heavy naphtha containing some of the kerosene hydrocarbons, and the first distillate of kerosene containing some naphtha. The latter product is accordingly placed in a still heated by steam, and the naphtha distilled from it. The separation of the heavier hydrocarbons from the crude naphtha takes place in the subsequent process of distillation to which the product is subjected. From Pennsylvania crude oil, the yield of products is substantially as follows: The crude naphtha is redistilled by steam heat in stills of the cylindrical or cheese-box form, holding about 1,000 barrels. This treatment is often conducted in another refinery, for several firms confine their operations almost entirely to this branch of the manufacture. The naphtha may thus be divided into four products, known as gasoline, and C, B, and A naphthas, but gasoline is itself sometimes further subdivided into cymogene, rhigolene, and "gasoline." By the distillation of ordinary gasoline and condensation of the first distillate by means of a mixture of ice and salt, Mr. Merrill first obtained rhigolene (so named by Dr. Bigelow), which has a density of 94° B., and a boiling point of 65° F. Cymogene, which is similarly obtained, is said to boil at 32° F., and to have a density of 110° B. (Sadtler). In some instances the following are manufactured : : Density Sp. Gr. Use. 2. Gasoline, 3. Boulevard gas fluid, zoline, 88° to 86° 0.636 0.642 to 0·648 0.682 For surgical purposes For air-gas machines. 4. Primecity naphtha (ben- 73° to 68° 0.692 to 0.709 For sponge lamps, &c. 1 Petroleum: its Production and Products, 1893. The percentage of these products varies, but as a rule amounts to about 25 per cent. of the first three collectively; rather over 25 per cent. of the fourth, and about 40 per cent. of the fifth. Of rhigolene the crude naphtha frequently yields but one-tenth of 1 per cent., and of gasoline from 1 to 3 per cent. By other refiners the products are classified as follows: The kerosene distillate is chemically treated to remove its unpleasant odour and colour, and to eliminate those impurities which would otherwise cause it to quickly become darker in colour. The first operation consists in treatment with about 1 per cent. of sulphuric acid of 66° B. (1.767 specific gravity) in tall cylindrical iron vessels, which are usually lined with lead, as otherwise, especially if the oil contain water, the iron would be attacked. These vessels, which are termed agitators, are often as much as 40 feet high by 20 feet or more in diameter, and have a capacity of from 1,200 to 1,800 barrels. The distillate, free from water and not exceeding 60° F. in temperature, is pumped into the agitator, and the acid, which is admitted in the form of a shower through a perforated leaden pipe, is thoroughly mixed with the oil by means of an air blast admitted at the base of the agitator. In many refineries, the acid is added in three portions, a very small quantity being first used to remove the mechanically suspended water from the oil, and the second and third portions being allowed each to act for about forty-five minutes, and to settle for about an hour before being drawn off. To remove the acid still remaining in the oil, a shower of water issuing in fine streams from a perforated pipe at the upper part of the agitator, is allowed to fall through the oil, without agitation, for about four or five hours. A final washing is then effected with agitation by the aid of the air blast. The oil is lastly agitated with 1 per cent. of a solution of caustic soda (12° B.), this operation being sometimes followed by washing with water. It is then "sprayed," if necessary, and run into shallow tanks for exposure to light, as previously described (see p. 342). The time occupied in the chemical treatment has been given as follows: |