CHAPTER VII. COTTONSEED PRODUCTS.-Continued. Bleaching Summer Yellow Oil. Refining of Crude Cottonseed-oil. The Refining-kettle. Apparatus of Refining. Use of Caustic Alkali. Procedure of Refining. Finishing Refined Oil. Influence of Heat on Refined Oil. Classification of Summer Yellow Oil. Products of Summer Yellow Oil. Winter Oils. Classification of Winter Oils. Nature and Valuation of Fullers' Earth. Press-cake. Cottonseed-oil Soap-stock. Determination of Fatty Acids, Free or Uncombined Oil, and Total Fatty Acids in Cottonseed-oil Soap-stock. Refining of Crude Cottonseed-oil. The necessity of working up seed promptly to avoid deterioration and subsequent impairment of the oil, the inconvenience and cost of gathering and shipping a bulky article, the greater convenience of shipping the crude oil, the necessity of the return of the by-products of oil-milling, viz., meal and hulls, to the soil that has produced the seed, the superior skill and experience, hence its scarcity, required in refining crude oil, the necessity for the fullest efficiency of operation of refining on as large a scale as is consistent with the greatest economy, represent, in so far as relates to the production of crude cottonseedoil as a finished product, the natural gravitation of the forces of production to the source of the raw material. Hence we find in the growth of the industry a rapid multiplication of crude-oil mills in the most desirable sections of the cotton belt for the receipt of seed, by wagon, water, and rail, and likewise the establishment of refineries at centrally located points for the receipt of the crude oil by rail and for the distribution of the products of refining. The real advancement of the last twenty years in the cottonseedoil industry has been made by the refinery. While there have been many improvements in the machinery of the crude-oil mills, the process is to-day practically what it was many years ago, but when we turn to the refinery, the tremendous strides which have been made in the improvement of the refining methods result in a product so superior to the article produced years ago, that industries utilizing the oil, on account of this improvement, can use greater quantities of the oil than ever before. The Refining-kettle. The agent used for refining is caustic soda, which is fully described in Chapter VI. The apparatus used is a plain cylindrical tank, or kettle, with conical or flat bottom, or with bottom slightly dished to facilitate removal of last traces of sediment. The kettle is provided with a swing-joint, or siphon pipe, located at a convenient level on the side of the kettle, for the decantation of the refined and settled oil. Below the swing-joint pipe and at a convenient distance from the bottom of the kettle may be another outlet to provide for a more complete separation of the oil from the sludge, or sediment. In the bottom of the kettle is a valve for the removal of the precipitate obtained on refining. The contents of the kettle may be heated by either exhaust or live steam in either open or closed coils, or both. Air for agitating the contents is introduced by means of a crisscross pipe, provided with openings, which connects with a pipe running over the side of the kettle and leading to an air-pump or compressor. Caustic soda is run into the kettle by gravity directly from the lye-tanks, where it is reduced to the required density, through a perforated pipe which distributes it uniformly over the surface of the oil. The capacity of the refining-kettle varies, the smallest being that which will provide ample room for working and will produce of supernatant refined oil a volume at least equal to the capacity of a tank-car, viz., 125 barrels, this being the smallest amount for profitable handling. The maximum size will be determined by facilities for heating and agitation and by results obtained with, larger batches than that of a tank-car. The prime essential in refining is intimate contact of alkali and oil at the proper temperature. The crude oil may be transferred to the refining-kettle from the storage-tank either by pump, or by gravity where the arrangements of the piping system permit of the latter choice. Apparatus of Refining. The equipment of a refinery is most conveniently installed in a three-story and basement building. This construction permits the handling of much of the material by gravity and the separation of different stages of the work into corresponding departments. On the third floor are located the refining-kettle and the caustic-lye tank, from which lye at the density required may flow by gravity into the refining-kettle. On the second floor are located the finishing-kettle and the bleaching-plant, and in a separate portion of the same floor, the kettle for working up the soap-stock. On the first floor are located pumps for transferring crude and refined oil, and here the products of refining are discharged into their packages. In the basement are located receiving-tanks for crude oil, into which oil may be discharged by gravity from barrels or tank-cars and from which it may be pumped as desired either into the refining-kettle or storage-tanks. The caustic melting-tank may be also located in the basement, from which the strong lye is pumped to the top floor and diluted to the density desired. Use of Caustic Alkali.-The function of caustic soda in cottonseed-oil refining is to combine with the free fatty acid present in the crude oil as a result of the decomposition of the originally neutral oil. The product of this combination is a true soap, sodium oleate, and is the same as that which is formed when cottonseedoil is saponified with caustic soda in soap manufacture. In the combination of free vegetable acid together with more or less oil and caustic soda, with the combined agitation and heating, the coloring-matter of the crude oil and the mucilaginous and albuminous matter unite to form a coagulum which, on allowing the treated oil to stand, settles to the bottom of the kettle together with unused alkali, which is added in excess, and more or less oil mechanically mixed. This precipitate constitutes the raw material for the commodity that comes on the market as "cottonseed-oil soap-stock." The amount of caustic soda, both in the absolute quantity of sodium hydrate and in the volume of the solution required for refining, is subject to wide variation. A quantity of caustic-soda solution requisite to saturate the free acidity of the crude oil as ascertained by analysis, is insufficient to effect the purification desired, so an excess must be added, which must be determined by experiment with a sample of the crude oil. The percentage of free fatty 34 acids will vary from 0.4 per cent. to as high as 30 per cent., but the average is in the neighborhood of 2 per cent. The free acidity is estimated in terms of oleic acid, CHO2, molecular weight 282. If in a batch of crude oil weighing 50,000 pounds, the free fatty acid content is found to be 2.5 per cent., the weight of free oleic acid is, therefore, 1250 pounds. One molecule of oleic acid combines with one molecule of sodium hydrate, NaOH, molecular weight 40; therefore, according to the following equation: Oleic acid (282) : Sodium hydrate (40) :: 1250 pounds : x; x, the weight of sodium hydrate required for neutralization, equals 177.3 pounds. This weight of chemically pure caustic, expressed in terms of the commercial grade of 74°, which contains but 95.48 per cent. of available caustic, equals 185.7 pounds, which is approximately the weight contained in an equivalent number of gallons of caustic-soda solution of 15° Bé. made from 74° caustic. The percentage of caustic-soda solution of the density desired. is arrived at by refining-tests on samples, using solutions of different strengths and proportions, until the results desired on a practical scale are obtained with the sample. According to the character of the oil the density may vary from 6° Bé. to 25° Bé., with the percentage of the solution necessary in inverse proportion to its density. It is necessary that the alkali be uniformly distributed over the surface of the oil, which is effected by means of the spray-pipe previously mentioned, and that during the addition the oil be kept in agitation, without which precaution the caustic-soda solution, in virtue of its greater density, would sink at once to the bottom, and intimate contact with the oil would then be difficult to attain. Procedure of Refining.-After the batch of crude oil has been accurately weighed and a sample taken for the refining-test, it is transferred to the refining-kettle, which has previously been thoroughly cleaned. The methods of manipulation vary greatly with individual refiners. By some the oil is first heated to 85° Fahr., when caustic-soda solution of required quantity and strength is added, meanwhile keeping up vigorous agitation; the more quickly the caustic is added the better. After the addition of the solution, |