The Winslow mail., 1915-05-08
NoVacuIite Found Near Hot Springs
Equals Abrasives Imported
from Turkey.
INDIANA STONE MUCH coARsER
Mica Schist Rocks from New Hamp-
shire and Vermont Keep
Scythes Sharp.

Inc proper sharpening stones or dD-
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. C. The exhibit
shows specimens of the crude and
partially prepared stones and the fin
ished products ready for use, as well
as a 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 This
Arkansas stone is known as noyaculite
and occurs in two or three grades, in
tended for use with certain tools The
hard, flint like stone should be used
I 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 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 engrayers and honing
/ er grain than the novaculite of ar
kansas, but nevertheless, quite uni.
/ form. 1t may be used with either oil
| or water, and is useful for sharpening
household cutlery, penknives 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 dark gray color and
composed of very thin sheets of mica
and quarty crystals interlaminated
The grit of the schist is not as sharp
as that of the sandstone, because it
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 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-
quire stones with these qualities, and
consequently much schist rock is
made into scythestones. Some of the
fine grained schists which produce
well-fnished edges are made into car
penter's bench stones.
A simple experiment made about Is
years ago led to the discovery of Car
bOrundum and Srystolon; by heating
mixture Of salt, sand, sawdust and
powdered coke in an electric furnace
the Yariegated 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 dia-
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 a 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, to 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- .
tai grains are used by gem and stone
cutters and for saving building
stones.