The

HE manufacture of flour from wheat, or, indeed, any

Tstarchy material, is purely mechanical. Chemistry enters

only to the extent of a few simple tests which are employed to ascertain what sort of finished product the mechanical process is bringing about. The process of cereal milling consists in running cleaned and moistened seed through a series of chilled iron rolls, the first sets usually about four which are corrugated, cracking the kernel, while the succeeding sets of smooth rolls, each pair being run more nearly together as the end of the train is reached, gradually reduce the cracked grain to a finely divided powder which we call flour. There are sifting devices innumerable ranging as to size from those of relatively large opening used in the preliminary cleaners to separate the grain from the bits of gravel that the threshing machine sends to market to the almost imperceptible mesh of the silk bolting cloth, with 125 threads to the inch, used for "dressing" patent wheat flour. There are "purifiers" which are essentially sieves used in conjunction with a draft of air from a blower, the former taking care of the large particles and the latter handling the light, fluffy material incident to each step in the gradual reduction of "purified middlings" to flour. There are dust collectors (flour dust, not dust from the floor), to which are sent the dust from the flour handled by the pneumatic element of the "purifiers."

As all seeds contain a germ-else they would be but poor specimens of seeds-and as all germs are rich in oil, and as all vegetable oils oxidize and rancidify, the germ is not considered a desirable part of a finished flour. Also, as all seeds are enclosed in an envelope of cellulose, which is termed "bran," and as cellulose is not digested by the human stomach, although cattle and swine handle it in good shape, the outer covering is removed from the finished flour-except in certain types prized more for their medicinal value than for their dietetic worth. It is unfortunate that vegetable oil rancidifies, as it is a good food; also it is unfortunate that the bran of cereals is relatively rich in mineral salts, as its abstraction leaves the flour to that extent deficient in that regard. However, these objections are more academic than practical, as the average mixed diet furnishes an ample quota of both fats and mineral salts.

Historical.

It is hardly necessary to point out that the pulverization of grains of all sorts is an extremely old custom. In archaeological exploration it is almost always possible to find the crude mortars in which, with a rough stone for a pestle, the grain was hammered into the form of coarse flour in the early days. In working with a mortar and pestle one naturally finishes the process of pulverization with a rotary motion of the pestle. No doubt our early ancestors noticed this phenomenon. At any rate, they long ago devised crude methods for imparting a rotary motion to their pulverizing machines, both members of which were rough field stones. The arrastre of Mexico, the primitive gold mining machine of that country, is a case in point. Before the Christian era crude stone flour mills had been invented in which a heavy disk of stone on a vertical axis was made to revolve upon a circular bedplate of like material. The grain was fed through a hole pierced in the upper stone, the outlet of which fed the raw grain to that part of the bedplate near the spindle. The finished flour came out from between the two faces of stone and was gathered in a trough fashioned at the rim of the circular bedplate. Any one who has seen the magnificent Italian film, "Cabiria," will recall the scene in which the powerful slave is compelled to run the flour mill of those early days. The film was of the twentieth century, but the flour mill was a true copy of those used before Christ. Examples of this sort of mill can be seen in the ruins of Pompeii. Such a machine leads by easy steps to the stone burr mills of comparatively recent times.

Modern Mills.

Flour

A stone burr outfit consists of two stone disks, the faces of which very nearly but, not quite meet. In both upper and nether mill stones are grooves running from the center out and toward the rim in such manner as best to aid centrifugal force in forcing the product toward the edge. The "dressing" by hand with a steel chisel of a slightly worn burr stone is a task of considerable delicacy. While the burr mills are still used to a considerable extent for grinding feed, they have given way in great measure either to a type making use of the same general principle, the attrition mill, or to the chilled iron cylinders employed in "Hungarian roller milling." The attrition mill consists of two steel plates suspended with their faces vertical. These plates are set very close to each other and revolve in opposite directions. The faces of the plates are grooved or otherwise roughened and as they revolve at high speed they are extremely effective wherever they can be used.

The Hungarian system of roller milling is well called the "gradual reduction process," as its main point of difference from the old burr mill lies in the use of many sets of chilled iron rolls and the gradual accomplishment of what the older type of mill accomplished between the upper and the nether millstone, and in one step.

The modern American flour mill is now fairly well standardized. The first roller mill built in this country, that of Governor C. C. Washburn, was erected in 1878. The process was at that time by no means accepted as definitely adapted to our wheats. This is proven by the fact that when, during the first year of the operation of the new mill, one of the older mills of Minneapolis was destroyed by a flour dust explosion it was replaced by the customary stone burr. For about thirty years, however, American millers generally have It has been found parbeen using the Hungarian process. ticularly well adapted to the hard spring and hard winter wheats and, more latterly, to the durum type of wheat. While stone burrs produce a fair grade of flour from soft winter

wheats, the miller is not able to produce a satisfactory flour from. hard wheats with such a mill. This is due to the fact that the stone burrs grind into flour practically all of the wheat kernel and a flour made from the entire hard wheat kernel on burrs is not fully satisfactory because of its high ash content and dark color. This objection is overcome by the employment of the "purifiers" which have been an integral part of the roller milling process, but have now been replaced in some mills by other specially designed machines to do the same work.

In the modern mill using the Hungarian process the rolls are of chilled iron, machined and polished to a mirror-like surface. They revolve on a horizontal axis and run in journals well adjusted and cared for, each set of rolls being housed in a wooden cabinet to guard against filling the air of the mill with flour dust. Each pair of rolls is held in proper adjustment by means of heavy spiral springs which furnish a certain amount of elasticity to the compression of the wheat and automatically compensate for any unevenness in the flow of grain or incomplete flour fed to them. The break rolls are separated, each from the other, by slightly less than the smallest diameter of the seed which is to be crushed while the finishing rolls very nearly meet. The sets in between, some six or seven in the average mill, are of varying distances of separation, the distance decreasing as the finishing rolls are approached. At every step the product is run through purifiers, the purpose of which is to draw off by means of drafts of air the light, fluffy flour and to detect and start back for re-grinding any particles of cracked grain larger than should be the case at the particular stage of the process at which the "purifier" is placed. That part of the product which passes through the screen is used as the feed for the set of rolls next in the series.

The force of gravity is made use of as much as possible in conveying the grain through a mill, although the modern blower handles all grains satisfactorily and economically and with but little regard for direction. In the future there may

be more pneumatic handling of grain and flour than there will be of the older method of small metal buckets fastened to a flat-link chain running on sprocket wheels, or to a belt running on pulleys.

In blending flours the "worm" or screw conveyor is often used. This is a metal spiral revolving slowly in a circular box but little larger than its own diameter. By the use of an open bottom wedge-shaped hopper two or more sorts of flour can be fed simultaneously to the revolving worm and at the end of a journey of a dozen feet or so the blending is remarkably uniform.

Course of Wheat Through the Mill.

After the wheat has been received at the mill, it is run through separators which eliminate all particles larger than the wheat by allowing the wheat and any smaller particles of matter to drop through holes which are just large enough to permit their passage. This partially cleaned product is next run over plates pierced with holes a trifle smaller than the wheat, which results in the removal of all particles smaller than the wheat berry. Magnetic separators are used to catch any pieces of metallic iron, and it is surprising to see how many tiny bits of baling wire and other metallic fragments are obtained by the huge magnet over which the stream of wheat slowly passes. The particles removed by the sieve separators are for the most part seeds other than wheat such as cockle, mustard and dock.

The "beard" of the wheat kernel-the fine hairs at its smaller end-and the adhering dirt are removed by passage through brush or scouring machines especially designed for the purpose, which machines also remove by abrasion a small but appreciable part of the outer coat or bran.

The wheat in some mills is next run through washers where by means of water and brush-like attachments it is freed as nearly as possible from adherent dirt. It is then run into tempering tanks, which are large steel cylinders set upright. Here the wheat is soaked in tepid water until it is