century, and is still so common, especially in small ‘customs’ mills, that a brief description of this process of milling is given. The millstones are made of buhr-stone, a form of silica as hard as flint but not so brittle. They are usually from four to six feet in diameter, and each consists of a number of pieces strongly cemented and bound together with iron hoops. The grinding surface of each stone is furrowed or grooved, one side of each groove being cut perpendicularly and the other side being inclined to the surface of the stone. The grooves on each stone are furrowed exactly alike: thus the sharp edges of the grooves on the one come against those on the other, and so cut the grain to pieces.
Fig. 1. OLDER FORM OF FLOUR-MILL.
Fig. 1 shows a section of a flour-mill.
The millstones are at a, the lower of which
is firmly fixed, and the upper is made to revolve,
on a shaft which passes up through the lower one,
at a speed of one hundred revolutions per minute,
more or less. Motion is communicated by the
spur-wheel b, which is driven by a water-wheel
or other power. The grain, previously cleaned, is
supplied to the millstones by means of the
hopper, c, connected with which there is a valve, d,
for regulating the supply. Passing through a
hole in the centre of the upper millstone, it comes
in between the two, where it is ground, and
thrown out on all sides by means of the
centrifugal force. The millstones are, of course,
inclosed, and the flour passes down through the
spout, e, to the worm at f, which carries it along
to elevators, g. These raise it up to the floor, on
which the dressing-machine, h, is placed. This
is a cylinder, which was formerly made of
wire-cloth of various degrees of fineness, and
consequently separated the flour into different
qualities, but no part of it large enough in the openings
to let through the bran, which passed out
at the end. Silk is now preferred to wire-cloth
for dressing the flour. Hoppers, i, are placed
below the dressing-machine, by means of which
the flour and bran are filled into sacks; No. 1
being fine flour; No. 2, seconds; and No. 3, bran.
Fig. 2. SECTION OF A MODERN ROLLER MILLING MACHINE.
The third and final step in the development of
milling processes was taken when rollers were
substituted for stones to perform the grinding
process. Iron rollers were generally used at
Pest to grind wheat before 1840, and, under the
name of the Hungarian system, rapidly spread
throughout Europe. As early as 1810 Ignes Paur
of Austria invented a middlings purifier which
is described below. It is claimed that in 1868-70
E. N. LaCroix, a French miller, independently
invented a system of roller-milling similar to
the Hungarian system, and installed it in one of
the great flour-mills of Minneapolis. Its
introduction marked an epoch in the production of
American flour. The essence of this new process
is the substitution for a single grinding between
millstones of a succession of grindings between
several sets of iron or porcelain rollers. The
wheat is gradually reduced by running it through
six or seven different sets of rollers, a thorough
process of winnowing or sifting intervening
between the grindings. As a musty odor and
dark color are given to flour if it is heated during
the process of manufacture, the rollers are
kept cool.
Fig. 3. MAGNIFIED SECTION OF GRAIN OF WHEAT.
Wheat is made up of a central portion of starchy
cells, A in Fig. 3, surrounded by gluten cells, B,
containing nitrogenous or proteid matter, which
builds up tissue. The germinal portion shown
at C contains phosphates, which possess great
food value, as do the inner layers of the husk, D.
The exterior coatings, which are of a fibrous or
woody nature, are, on the other hand, quite
indigestible while passing through the alimentary
canal of a human being. That portion of the
wheat between the central starchy portion and
the husk is called the middlings. This is the
most valuable portion of the wheat for making
not only a nutritious but also a light bread.
Two grades of wheat are known to the miller: Winter wheat, or that sowed in the fall and coming up in the early spring; and spring wheat, which grows during the summer, and is harvested in the fall. The winter wheat, whose
