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nor to change lower grades into higher ones." Of the many processes for bleaching, the only ones having any industrial value seem to be “based on the use of peroxide of nitrogen, prepared either by chemical action or by the action of a slaming arc upon atmospheric air.’’’ Flour naturally grows whiter as it grows older. The Dust Collector.—The milling of wheat always produces flour dust. The ignition of these particles suspended in the air caused disastrous explosions in the Minneapolis mills during 1877-78. This led to the development of the dust collector, the first form of which was a filtering diaphragm. Its essential principle is now the vortical or rotary air current, which masses and precipitates smaller particles than the finest filter could arrest. The Grades of Flour most usually made are four in number: (1) Patent; (2) first class; (3) second class; and (4) red dog. The feeds comprise the remainder of the milled product. The basis of flour grading is mainly its purity, that is, its freedom from the bran and germ portions of the wheat kernel. The best flour comes from the center of the grain. The strongest gluten is nearest to the outside of the kernel, but the outside can never be perfectly separated from the bran. The degree of purity varies with the different processes of milling. The equipment of the miller, his special process of milling, and the market to which his products go determine the number of grades of flour that he makes. He may omit some of these four grades, or he may further separate them and make a larger number of grades. Patent flour, for example, may be separated into first and second patent. The requirements of some buyers are for a flour that is sharper or more granular, while those of other buyers are for a flour with fine soft granulations and very white color. After all of the flours have been collected from the various machines into their respective grades, they are conveyed to the packing bins, from the bottom of which they are drawn by automatic power packers into packages varying in weight from 2 to 280 pounds.

1 Letters, Frank W. Emmons, Washburn-Crosby Co., and John E. Mitchell. Alsop Process Co. * Sci. Am., S. 61:25:263 (1906).

The Large Typical Mill of the Winter Wheat Belt.”—A milling plant of five buildings and six grain storage tanks or silos, having a storage capacity of 300,000 bushels and a daily milling capacity of 1,500 barrels, involves a capital investment of about $200,000. The buildings include: The mill, 88 by 42 feet, and five stories high; the warehouse, 98 by 42 feet, and three stories high; the power house, 68 by 72 feet, and 25 feet high, with a tile smoke stack 125 feet high; and the grain elevator, 48 by 42 feet, and 118 feet high. The steel tanks or silos for storing the grain are each 30 by 60 feet. All of these tanks are connected at the top with a gallery for delivering the grain, and at the bottom with a conveyor belt for discharg— ing the grain. Four thousand bushels of grain can be received and discharged per hour. It is moved from car to elevator and conveyors by means of steam shovels. The number of men required when the mill is running day and night consists of 3 officials, 5 office employees, and 35 other employees.

When the grain is received in the mill, it is given one cleaning over ordinary separators, and then stored. Before grinding, it is given such additional separations as may be required. It takes about one hour to complete the milling. The finished product is either loaded into cars or stored in the warehouse, and it is disposed of to the local and foreign trade. The average amount of wheat carried is about 200,000 bushels, and the probable average amount of flour on hand is about 10,000 barrels. Mills located at interior country points depend largely for their supply of wheat upon the deliveries of farmers and of country grain merchants in contiguous territory. About 5 per cent of the capital invested is devoted to products other than those of wheat. About $25,000 of cash must be ready for immediate requirements. Five to 10 per cent of the business is done on credit. The average expenditure for salaries and wages amounts to about $45,000 per year. Approximately 5 per cent of the original cost is annually charged to the depreciation of plant and equipment.

One of the largest mills in the world is the “A” mill of the Pillsbury-Washburn company of Minneapolis. The ordinary capacity of this mill is 15,000 barrels of flour per day, but 15,500 barrels have been ground. The company is now expending $500,000 in enlarging the plant so that it will have a capacity of 17,000 barrels. The maximum milling capacity of the Minneapolis mills aggregates a total of 82,765 barrels daily, and this is to be increased to over 90,000 barrels before the close of 1907. The great progress of the industry is best understood when it is remembered that the first crude mill of the ancients could not produce over 3 bushels of partly ground meal in one day. Later, the Greeks ground from 5 to 10 bushels of meal per day. The Flour Yield of Wheat.—Soft wheat weighing 64 pounds per bushel has been found to yield about 80 per cent of flour, while that weighing 54 pounds yields about 65 per cent. The heaviest hard wheat yields about 74 per cent of flour, while the lightest yields 67 per cent. McDougall found that India wheat yielded from 77 to 81 per cent of flour, English wheat 65 per cent and American wheat 72 per cent. The flour yield will, of course, vary from season to season, for it is dependent upon the quality of the wheat. In 1905, it required 4 5-6 bushels of wheat to make a barrel of flour in Minneapolis, while in previous years it required only 4 1-3 bushels. According to a miller in Kent, England, 4.2 bushels of wheat made a barrel of flour in 1876. Two centuries ago in New England, it required between 6 and 7 bushels. There has been a continual increase in the amount of the highest grade of flour obtained. Toll.—The first toll dish was the hand of the miller. In England in 1300, the toll was one-twentieth of the wheat ground. During the middle of the seventeenth century, the miller's toll in New England was one-sixteenth of the wheat ground. Of the thirteen original colonies, all but New York and Pennsylvania had laws for regulating tolls, which varied from onefourth to one-sixteenth. The amount of labor required to grind a barrel of flour at the close of the seventeenth century, if expended at the close of the nineteenth century, had a market value approximately equal to the cost of grinding a barrel of flour in the latter period. In 1891, the legal toll in Minnesota was one-eighth. Measured in wheat, this is twice the toll which the miller received in New England 200 years ago. In the cities and large towns, however, where wheat was exchanged for flour on a cash basis, the cost of a barrel of flour would

1 These data are furnished by the Kansas Milling Company, Wichita, Kansas.

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purchase enough of No. 1 hard wheat to make 1.5 barrels of flour. In some places in Minnesota only one-eighth, the legal toll, was taken, and the amount taken varied from this to onethird at Minneapolis. It was stated that 700 years ago the English miller with his small toll made several times the profit that the Minneapolis mills made in 1891. Geographical Location and Extent of Milling Industry.—The first development of the milling industry in the United States was in New York and in Pennsylvania. These states exported flour to the other colonies and to the West Indies. They long held first rank, and still mill large quantities of wheat, having held fifth and seventh places respectively among the flour producing states of our country in 1900. In the number of establishments and the amount of capital invested, they have always held first rank, at least until after the early nineties. Virginia, Ohio, Illinois, Missouri, Indiana and Michigan later assumed importance as milling states. Thirty years ago, the flours most sought after in the home and foreign markets were those of St. Louis and the south. St. Louis was then much the largest flour-making center of the United States. The improvements in milling processes changed the whole situation, for the best flour was now made from spring wheat. In the great rush to obtain Minnesota flours, St. Louis and southern flours were for the time forgotten. The first Minnesota mill was erected in 1823. The development of the milling industry in Minneapolis was most remarkable and rapid, chiefly by reason of the cheap water power obtainable from the falls of the Mississippi river. Other factors were the nearness of the wheat fields and the subsequent improvements in the art of milling. Before 1860, the annual output of the Minneapolis mills was about 60,000 barrels. This increased to 98,000 barrels in 1865, 193,000 in 1870, 585,000 in 1873, and over 1,000,000 in 1876. A conflagration then impeded the industry by destroying many mills, and it was not until 1879 that the output again exceeded a million barrels. By the end of the century, the average annual output was approximately 15,000,000 barrels. As the milling industry developed, it moved toward the wheat fields. From 1877 to 1888, the receipts of flour at Buffalo were 22 per cent of the receipts of both wheat and flour, while from 1889 to 1898 they were 42 per cent. As the freight rates per

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