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