Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/360

 346 FLOUR greater than B. Smooth surface rollers are mounted to press hard against each other, and are made in some cases of polished chilled metal ; and in other instances cylinders of porcelain are employed. Their principal function is for the reduction of purified middlings and semolina, and when no differential motion is given the action is simply that of squeezing, but when the opposing rollers revolve at different rates of speed a grinding effect is further superadded. A roller mill which has met great and sudden public accept ance is that invented and patented by F. Wegmann, a miller of Naples. In Wegmann s mill, fig. 7, porcelain rollers are employed, there being two pairs fed from opposite ends of one hopper in the machine figured. This machine possesses a self-acting pressure and a differential motion ; but its most valuable feature consists in the employment of porcelain for rollers, by which a surface at once exceedingly hard and slightly rough or porous is secured. It is claimed for these rollers that, FIG. 6. Section of Toothed Rollers. Fio. 7. Wegmann s Roller-Mill. acting on middlings, they produce, with less expenditure of power, more and better flour than can be obtained by either stones or metal rollers. For the grinding of fine middlings English experience is, however, in favour of chilled iron rollers as the best. The roller mills have not yet been long enough in operation in Great Britain to enable any safe conclusion to be drawn as to their adapta bility to British milling ; but though the system originated only within the last few years, it has in the meantime practically superseded all other methods in the Austro- Hungarian districts, where milling is carried to greater perfection than in any other part of the world. To show the progress made in the introduction of roller mills in Britain, it may be noted that, while in January 1877 there was only one Wegmann s machine in operation, there were by the close of the year 350 in various mills through out the country. The Disintegrator. Under this name a form of machine was invented and introduced a few years ago by the late Thomas Carr for, among other purposes, the manufacture of Hour. Carr s disintegrator consists of a pair of circular discs of metal set face to face, and studded with circles of projecting bars so arranged that the circles of bars on the one disc alternate with those of the other. The discs are mounted on the same centre, and so closely set to each other that the projecting bars of ths one disc come quite close to the plane surface of the other; and they are inclosed within an external casing into the centre of which a spout passes by which the grain is delivered into the machine. The discs are caused to rotate in opposite directions with great rapidity, making about 400 revolutions per minute, and as the outer circle of bars is 6 feet 10 inches from the centre, they move at a rate of 140 feet a second, or about 100 miles per hour. The grain in passing through the machine is struck by the oppositely revolving studs with enormous force, a force which increases as the shattered grains approach the outer circles of studs, and it is almost instan taneously reduced to a powder which falls under the discs and is carried away by a spiral creeper. It is stated that one of these machines 7 feet in diameter is capable of doing the work of as many as 27 pairs of millstones, and they have been fully tested in the flour mills of Gibson and Walker, Bonnington, near Edinburgh, where two of them have been in operation for a period of seven years. Notwithstanding this success, however, the disintegrator has not met with general acceptance as a flour mill, having been introduced into only a very limited number of establishments. The following is a statement of the average results Messrs Gibson and W r alker have obtained by the disintegrator from old Scotch wheat and from a mixture of Baltic and Ghirka wheats respectively : Old Scotch. Flour 45 per cent. Semolina 26 Bran Hour 4^ Exhaust Hour 1 S Seconds 4 Parings 1 $ Bran 13 Black dust, &c 2|- Loss 1 Baltic and Ghirhi. 35 per cent. 36 41 11 33 2 13 3 11 100 100 The semolina is reground under stones, and yields a fine strong flour ; but it may be and sometimes is reduced by passing it again through the disintegrator. Qualities of flour. There appears to be at present some conflict between public demand, as indicated by the in creasing attention paid to the production of a fine strong white flour, and the current of scientific opinion expressed, though with some hesitation and doubt, in favour of whole meal or flour in which the richly nitrogenous outer portions of the wheat are retained. The fact that the outer portions of the wheat are richest in nitrogenous principle, and that also in a peculiarly active form, is indisputable ; but it has not been satisfactorily determined whether the nutritive value of that portion of the grain is exactly measured by its chemical composition. The condi tion of the nitrogenous substance, the amount and irritat ing nature of the ligneous tissue which accompanies it, and its peculiar influence on the other constituents of the wheat grain may and probably do affect its value. It is certain also that white flour is deliberately preferred by the labour ing population, whose instinct is probably right, and it is also preferred by and for many purposes indispensable to the baker and cook. Good flour should present the appearance of a pure uniform white powder, only faintly tinged with yellow, free from all grit and lumps; and when