scows and barges called “flats.” Many of the large establishments transport the crude oil in what are called tank cars. These are ordinary platform cars, upon each of which are constructed two large tanks. These are filled at the wells and carried in long trains to all parts of the country. When they reach their destination they are emptied into iron tanks, often of immense size, when the oil is again allowed to settle so that the last traces of water and any sand or other impurity may be removed.—The apparatus for manufacturing petroleum consists of stills of various forms and sizes, with worms for condensing the vapors, and agitators in which the oils are treated with chemicals. The stills are usually cylindrical, and are placed either on one end or horizontally. They are either cast iron with wrought-iron bottoms or made wholly of boiler iron, and hold from 1,000 to 80,000 gallons. The smaller sizes are heated by one fire, the larger by several. Sometimes the stills are encased in wood or brick work to prevent loss of heat. Superheated steam is frequently introduced into the stills, especially during the distillation of the heavy oils. The very large stills recently constructed are used for carrying on the process known as “cracking.” After the removal of the gasolene and different grades of naphtha, the remainder is subjected to destructive distillation. Any method that will heat the vapors above the boiling point of the oil will decompose the heavy oil, with deposition of carbon and the production of lighter oils richer in hydrogen. This effect has been produced by distilling under pressure; but the method usually employed is the one before mentioned. The distillation is kept up in such a manner that as the temperature increases and the heavy oils pass into vapor, the vapors are condensed upon the high dome of the still and either fall back in drops or flow down the sides. In either case they reach the surface of the boiling oil beneath, which has meantime been heated above the boiling point of that which falls upon it. The result is a decomposition of the latter into a more volatile oil containing proportionally more hydrogen, and carbon which is deposited. This process may be continued until nothing remains in the still but coke; but it is not usually carried to that point, as the coke is difficult to remove from the still. The tarry matter left in the still is known in commerce as “residuum.” The treatment of the oils is confined to the heavier kinds, including kerosene. The naphthas do not require treatment. In many establishments all the oils treated are alternately agitated with about 5 per cent. of strong sulphuric acid and the same amount of strong solution of caustic soda. In others, solution of caustic soda is put into the stills, and sometimes the soda is used solid. The sulphuric acid removes a number of unstable compounds, by decomposing some of them and uniting with others. The caustic soda removes the excess of acid and acid compounds, and leaves the oils pure. The odor of the crude distilled oils is exceedingly offensive; the action of the caustic soda removes these disgusting compounds, and gives the finished oils the peculiar balsamic odor by which they are distinguished. The spent sulphuric acid is technically known as “sludge,” and is used by the manufacturers of superphosphate of lime. The spent caustic soda is often recovered as a carbonate and reconverted into caustic soda. Nitric acid and bichromate of potash have also been used in place of sulphuric acid. In many of the older refineries the oil was exposed in shallow tanks beneath a skylight, in a manner exactly similar to the treatment employed for bleaching sperm oil. This is an admirable method for obtaining a complete separation of the last minute particles of caustic soda, but it is not equal to finishing by a last distillation, which is the method now employed in the best establishments.—The demand for gasolene for automatic gas machines has led to the establishment of a few manufactories in which this very volatile product is separated from the heavier grades of naphtha. Other separate establishments have been erected for the manufacture of paraffine and lubricating oils from residuum. These purchase the heavy waste products from the large kerosene manufactories, and by special processes convert it into useful commercial articles.—The manufacture of petroleum products from the crude oil is carried on either to obtain the largest number of products of the finest quality, or to obtain the largest yield of kerosene without regard to any other product. Probably the finest petroleum refinery in America, if not in the world, is that of the Downer kerosene oil company of Boston, Mass., and Corry, Pa., of which Joshua Merrill is the manufacturing chemist. Mr. Merrill began the manufacture of hydrocarbon oils for illuminating and other purposes as early as 1852, and from that date until the introduction of petroleum in 1860 a great variety of crude materials had been subjected to his skilful treatment with unvarying success. The works in Boston were originally built for the working of coal, boghead shale, and albertite, but since 1865 nothing but petroleum has been used there. All of the products enumerated above are manufactured there excepting paraffine lubricating oil and residuum. The branch establishment at Corry, Pa., is used only for the distillation of crude petroleum, the distillates being shipped to Boston for treatment. The processes employed at Boston are as follows: The crude oil is pumped from the tank cars into settling tanks placed under ground. After settling, it is pumped into large wrought-iron stills or upright cylinders which hold about 12,000 gallons each. In these stills the oil is heated by steam alone, which removes the various grades of naphtha, they constituting about 15 per cent. of the crude petroleum. These distillates are condensed in iron pipes
