The Winslow mail., 1915-12-03
ARKANSAS GIVES
BEST MILESTONE
NovacuIite Found Near Hot Springs
Equals AbrasiVes Imported
from Turkey.
INDIANA STONE MUCH CoARsER
Mica Schist Rocks from New Ramp.
shire and Vermont Keep
Scythes Sharp.

WuSISIOuS lOI uGdIly every puIpOSCt.
The proper sharpening stones or alb
rasives for use in various professions
and trades and in household work are
exhibited in the division of mineral
technology in the older building of
the United States National Museum
at Washington, d. G. Tie exhibit
shows specimens of the crude and
partially prepared stones and the fin.
ished products ready for use, as well
as series of photographs which illus
trate the operations of mining and pre-
pairing them.
Probably the first stone used for
abrasive purposes was sandstone, a
very widely distributed rock, and it is
still used today. It's coarse grit and
even grain first attracted attention,
while the rough edge that it gave was
all that was then required. With the
progress of the arts there began a
search for various stones which could
be used for sharpening objects of diff,
ferent sorts, so that today not only
sandstones, but mica schists, states
and emery stones are used, besides
several artificial compounds.
The hard, white, compact sand.
stones found near Hot Springs, Ark,
are among the best whetstones known.
equaling, if not SURPRISING, the Tur'
key stone which for years has been
considered one Of the best. 'TA;e
Arkansas stone is known as novaculit>
and occurs in two or three grades. in
tended for use with certain tools The
hard, flint like stone should be used
only to sharpen instruments made of
the very best steel, requiring very
keen edges and points, such as those
used by surgeons, dentists and jewel.
ers.
The other grades, although compos.
ed of the same ingredients, are more
porous, the sand grains are not as
close together and a rougher edge Is
given to the sharpened tool. Because
Of their more porous nature these
stones cut faster, proving suitable for
the finer edged tools of carpenters. ma
chinists and engravers and honing
razors.
stone made from sandstone Of a coars.
er grain than the novaculite of Pr.
kansas, but nevertheless, quite uni
form 1t may be used with either oil
or water, and is useful for sharpening
household cutlery, penkniyes or ordin-
ary carpenters tools. But since it is
easily cut and grooved by hard and
sharp steel, the fine instruments of
dentists and surgeons should not be
edged or pointed on this stone.
Scythestones and moving machine
stones are virtually all made from
mica schist rocks found in New Hamp,
shire and Vermont. These rocks are
generally of a dark gray color, and
composed of very thin sheets Of mica
and quarty crystals interlaminateG.
The grit of the schist is not as sharp
as that of the sandstone, because 1t
contains foreign material other than
SILICA, which prevents the quartz
grains from abrading freely. Mica
schist stones wear down quickly from
constant use-an ADVANTAGE rather
than a disadvantage, for as they wear
down, more of the hard SILICA grains
are exposed to do the sharpening.
Neither oil nor water is needed to keep
the pores Of the stone open as with
other milestone rocks. SCythes re-
duire stones with these qualities, and
consequently much schist rock is
made into scythestones Some of the
tna grained schists which produce
well-inished edges are made into car
penters bench stones.
A simple experiment made about Is
years ago led to the discovery Of Car
borundum and Srystolon; by heating
a mixture of salt, sand. sawduSt and
powdered coke in an electric furnace
the variegated colored crystals of Car
borundum and Srystolon were produc
ed. These crystals are extremely hard.
cutting glass easily, and, In fact, al
most any substance except the d1a
mond; are intensely sharp, and infus
ible at any known heat-properties
peculiarly adaptable for grinding pur
poses, and for refractory materials
The Carborundum and Sarystolon crys
tails are removed from the electric
furnace after a 36-hour run, washed
with dilute acid solution, ground and
sized.
Eight or 10 different sizes Of grains
are made from them. The graded
grains of these substances are mixed
into paste with bond Of porcelain,
water-glass, or rubber, and nodded In
to many varied forms Of stones and
wheels. After air drying, the raw
wheels ar put into kilns and baked,
and are then ready for use. There are
wheels for all kinds of work, varying
from feet in diameter for use In
foundries, tC one-quarter inch for den.
tai work Besides the wheels, these
hard sharp crystals are made into
razor and knife homes, paste for valve
grinding and glued to cloth to be used
like sand and emery paper. The crys~