Bourne Archive:
Muspratt: Bark Mills
http://boar.org.uk/aaiwxw3MusprattL4BarkMill.htm Latest edit 27 Dec
2010
The Bourne Archive
Muspratt’s Chemistry, Theoretical,
Practical & Analytical (ca. 1859)
Extracts Concerning Leather, 4: Bark Mills.
The web pages linked from this
introduction are from an article on tanning, under the heading ‘Leather’. The
original article is presented here in several web pages, respectively dealing; 1, with leather; 2, with tanning
materials; 3,
Sources of tannin; 4, bark crushing mills; 5, varieties of skin; 6, hide
preparation; 7,
the common tanning process; 8, finishing
processes; 9, fancy
and speciality leathers.
Vol. 2. pp. 508-9
To render any of
the foregoing materials 1 suitable for the present operations of the
tanner, it is necessary to bring them into a minute state of division, in order
that by the treatment to which they are subjected, they may the more quickly
yield up their tannin. With the exception of the inspissated 2
juices, this condition is gained by grinding or cutting machines which reduce
the roots, branches, or barks, to a fine powder. Numerous kinds of mechanical
adaptations have been introduced into this department, varying in simplicity
from old head-stone rollers 3, to very intricate arrangements. It would
require too much space to give even a curt description of these; suffice it
then that the principles on which they are constructed may be inferred from the
machines described here:—
Farcot’s
4 bark-cutting machine, extensively
used in 
Inside the fluted cylinders is a
longitudinal piece of steel, C, which delivers the bark to the revolving
knives, and at the same time acts by its sharp edge as a shears towards the
cutting knives. The cylinder which carries the cutting knives makes about one
hundred and thirty revolutions per minute, as also the feeding cylinders; and
the quantity of bark cut averages one thousand six hundred pounds per hour.
The chopped bark is
then passed to a mill for reducing it still further, and which is shown in Fig.
344. This machine is on the principle of Weldon’s
bark-grinding mill, introduced so far back as 1797. In this figure, A is a
conical drum of iron on the end of the shaft, D, which forms its axis, inclosed
7
in the cast-iron hopper, B B, where the coarse bark is deposited. This hopper
is firmly secured by screws to a flange, which runs all round the framework, v v, as shown at a a. In the top of the exterior is across beam secured by screws,
and having a socket in the middle part through which the axis of the drum
passes. The lower part of the shaft rests and turns upon a bed, C, upon the
stage, T, and regulated so as to have the cone, A, in position, by the side of
the bottom screws, a’ a’ and b. The inner face of the hopper, 
B, which is in close contact
with the revolving cone, is, like the latter, serrated or grooved, so 
that the bark passing down is more
minutely sundered. Fig. 345 shows the position of the two cutting surfaces with
respect to one another. The central drum makes twenty-five revolutions per
minute, and in the course of twenty-four hours grinds about eight thousand six
hundred pounds of bark. The cutting machine already described is capable of
supplying three grinding mills.
Another grinding
mill, very much used in 
Weldon’s, only that instead of grooves an arrangement of
sharp-edged teeth, both in the inclosed bell and hopper is employed. As the
bell turns by the power exercised upon the shaft, the teeth in the former,
revolving, also react on the principle of the shears with those of the interior
of the case, and the bark is very finely and rapidly reduced. Before the matter
is submitted to this machine, it is broken down by passing it into another
hopper adjacent to the former, in which there is a sharp-toothed hoop or curb,
and which divides the bark into pieces. It is moved at the rate of thirty to
forty revolutions per minute, whilst the grinding machine may travel at the
rate of one hundred and fifty. With this speed, communicated by a ten horse-power
engine, it will grind from one to two chords per hour. The bark is cut short,
without being reduced to flour, and thus it is more readily exhausted 8;
there is also the additional advantage that, should the bark be moist, it does
not become clogged like others.
Next Page: Varieties of Skin.
Commentary
1. ^ These are the barks, roots etc., of various
woody species, listed in part 3.
2. ^ This is a Late Latin-based word, meaning thickened
or condensed (OED).
3. ^ This would be a cheaply set up answer to the
need. A worn-out runner stone from a corn mill, mounted on an axle pivoted at
the centre of a circular stone track and propelled by a horse, would roll over
the track, crushing the bark. This design mimics those used for crushing woad
and cider apples. An elaborate woad mill is shown on Arthur Young’s page 175. A
clearer picture of the mechanism appears in Gatty’s
Aunt Judy’s Annual Volume (1883), page 551. The same principle is employed by
the olive-crushing mill illustrated here.
4. ^ This is probably a product of the mind of Joseph Farcot,
or possibly of his father Marie-Joseph.
5. ^ Together, these represent two of the three
views of an orthographic projection but as drawn, the plan represents a machine
designed the opposite way round from that of the sectioned elevation.
6. ^ This is the French form of the word helix.
It was screw-shaped.
7. ^ Inclose is a variant of enclose, derived
directly from Latin, while enclose came into English via French. It was once
more widely used but now restricted to some legal documents and Acts of
Parliament (OED).