of coal would be required to manufacture 400 sacks of flour.
The cost of this quantity of coal may be taken at, say, L12 (about
$58.32), and for cost of attending engine and boiler, cost of oil, etc.,
another L3 (about $14.58) per week may be added; so that, in this case,
the manufacture of 400 sacks of flour would cause an expenditure of L15
($72.90) for the steam motor. Therefore the cost of the steam motor per
20-stone sack of flour may be taken at 9d. (about 18 cents) per sack, if
an improved low grinding system is used.
"In this case it is supposed that about 55 per cent. of flour is
obtained in the first run, leaving about 30 per cent. of middlings and
about 12 per cent. of bran, which is finished in a bran duster. The
middlings are purified, ground over one pair of middling stones, then
dressed through a centrifugal and the tailings of the latter are passed
over one of the porcelain roller mills, whereas the other porcelain
roller mill treats the second quality of middlings coming from the
purifier. The products from the two porcelain roller mills are dressed
through a second centrifugal, and the whole flour is mixed into one
straight grade. Four pairs of stones are supposed to work on wheat, one
on middlings, and one pair is sharpening. The first run is supposed to
be dressed through two long silk reels. Of course, not every steam motor
has so low a consumption of coal as two pounds per hour per horse power;
it often amounts to three, four, and five pounds per hour.
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