The following estimate of the cost of the power required to manufacture
a barrel of flour is taken from the _Miller_. The calculation would
hardly hold good in this country owing to difference in cost of fuel
attendance etc., but is nevertheless of interest.
"The cost of a steam motor per 20 stone (280 lb.) sack of flour depends
entirely on local circumstances. It depends first, on the amount of
power expended in the production of a sack of flour, that is on its mode
of manufacture, and it depends, secondly, on the cost of the necessary
amount of power, that is, on the cost of fuel burned per horse power The
average consumption of coal of first class steam engines may be taken at
2 lb. per hour per indicated horse power.
"Supposing a mill with six pairs of stones, two pairs of porcelain
roller mills, and the necessary dressing, purifying, and wheat cleaning
machinery to require a steam motor of 100 indicated horse power to drive
it, then the average consumption of fuel in this mill would be 200 lb.
of coal per hour. Such a mill working day and night will turn out about
400 sacks of flour per week of, say, 130 hours, so that 200 X 13 =
26,000 lb. 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. In that case,
of course, the cost of steam power per sack is much greater than 9d. per
sack. A greater number of breaks does not necessarily increase the cost
of steam power per sack of flour. Although more machines may be
employed, each of them may require less horse power; so that the total
amount of power required for manufacturing an equal amount of flour may
not be greater in the case of gradual reduction.
"As, however, the cost of maintenance may be slightly greater in the
latter case, on account of a greater number of more elaborate machines,
the cost of manufacturing a sack of flour may be a little greater when
gradual reduction is employed, taking into account the total expenses of
the mill and interest on the capital employed.
"Water motors are generally a much cheaper source of energy than steam
motors, but they are not so reliable and constant as the latter. The
very irregular supply of water sometimes causes stoppages of the mill,
and often a reserve steam engine has to be provided in order to assist
the water motor when the quantity of water decreases during the summer
months. Wind motors were formerly extensively used for milling purposes,
but they are now gradually disappearing. They are too irregular and
unreliable, although they utilize a very cheap motive power. It is not
advantageous to expend a large amount of capital for a mill which often
is unable to work at the very time when there are favorable
opportunities for doing profitable business. Animal motors are too dear.
They are only suitable for driving very small mills in out of the way
localities."
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