134 PEGMATITES AND ASSOCIATED ROCKS OF MAINE.
In
the wet process the quartz may be crushed just as it comes from the
quarry, or it may first be highly heated in kilns and then fractured by
turning upon it a stream of cold water. The first crushing is effected
by jaw crushers, or if the quartz has previously been burned it may be
crushed in chaser mills. In a few mills the chasers revolve in wet pans
and are periodically stopped to allow the crushed quartz to be shoveled
out. After crushing, it is ground in "wet pans" provided with a
pavement of flat-faced quartz or quartzite blocks over which move
several large blocks of similar material, the crushed quartz being
pulverized between these blocks and the pavement. The grinding in wet
pans usually occupies about twenty-four hours, the load ground in a
single pan varying from 1,200 to 1,800 pounds. From the wet pans the
pastelike mass of quartz and water is drawn into settling troughs, the
first settlings being in some cases returned to the pans for finer
grinding. From the settling troughs it is shoveled out upon drying
floors heated by steam or hot air, or else it is dried in small pans
which are placed tier on tier on heated racks constructed of steam
pipes. Finally the dried material is bolted to various degrees of
fineness and packed in bags for shipment, or it may be shipped in bulk.
In
the dry method of treatment the quartz is usually crushed first in a
jaw crusher and then between crushing rolls. Quartz to be used for
filters and for abrasive purposes is then screened to various degrees
of fineness and is packed in bags for shipment. In the manufacture of
the finer grades for use in pottery, wood fillers, scouring soaps,
etc., the material after leaving the roll crushers is ground in tube
mills, either of the continuous or of the intermittent type. It is then
graded to various sizes either by bolting or by a pneumatic process
whereby the quartz powder is carried by a strong air current through" a
series of tubes and receptacles, the distance to which the quartz is
carried being dependent upon its fineness. There are no quartz mills in
Maine. Those nearest to that State are in Connecticut.
Uses.—Quartz
is used for a great variety of purposes, the principal uses being in
the manufacture of wood filler, pottery, paints, and scouring soaps. In
pottery the quartz serves to diminish shrinkage in the body of the
ware; it is used also in many glazes. Quartz for these purposes should
contain in general less than one-half of 1 per cent of iron oxide.
Finely ground quartz is used in paints in various proportions up to
one-third of the total pigment used. Its chemical inertness prevents it
from combining with other constituents of the paint and increases the
resistance of the paint to the weather. Crystalline quartz is superior
to silica sand for this purpose because the ground particles are highly
angular and tend to attach themselves more firmly to the painted
surfaces, thus giving the paint what is known as a "tooth" and after
some wear affording a good surface-
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