The Saint Paul globe., 1897-09-06

Prof. Dwight's description of his own
machine:
1.-THE object of this article is to eX-
plain in popular language the general
character and work of what is at least
one of the latest and most perfect ma
chimes for the cutting of minerals, rock
fragments, ether for scientific or lap1-
Diary purposes. A few preliminary eX-
plantations will be advisable.
First. as to the meaning of the
word cutting" as applied to this ma
chine. The so-called and wrongly call
ed cutting" Of gems in the lapidary
work Of jewelry, as the cutting of
diamonds, is really no cutting at all;
what is called "cutting" in such cases
Is really grinding" preceded in some
eases by the splitting off Of fragments
by the blows Of steel tools This grind
Ing is effected either by such hard pow
ders as emery, carborundum, or dia-
mond powder, or by rubbing against
some hard, solid surface (as by rub
blng one diamond against anotheD.
''True cutting of stone is effected
either by the edge of a revolving metal
lie cutting disk, or by an oscillating
metallic strip or wire, fed or treated
with an abrasive powder, the best Of
which is diamond powder. This cutting
Is practised by lapidaries in cutting
slips of ornamental stone, as for cam
eos This "petrotome'' has no concern
with the so-called cutting" in it's first
mentioned sense; it can hardly be of
any assistance to lapidaries in the
cutting" of small gems. The work
which it does Is essentially one Of true
cutting or saving of mineral sub
stances by a properly prepared thin
cutting edge. There are grinding and
polishing wheels, however, connected
with the machine used in preparing or
- finishing it's work. AS will be shown
hereafter, 1t can be of Importance to
lapidaries in its work of true cutting.
ga nisapprehension has also arisen
from the use Of the title rock-cutting
machine leading even to the absurd
assertion in some newspapers that 1t
has been used in cutting rocks con-
tanning gold by the ton, whereas a
piece of mineral as large as a man
head. would be an unusually large
niece for this kind Of cutting. The
fact is that, whereas the term rock,
both in popular language and in gen
eral scientific usage, refers to large
masses of mineral matter, on the other
hand it is the only general term avail
able in lithology for any mineral suit
stance which is a component OF the
great masses of the earth'S crust ana
generally a mixture of mineral species.
In this latter sense there is no refer
ence to size, and any small piece or
such material is called rock to dis
tinguish it from a simple mineral Whlch
does not compose crustal masses
"a rock-cutting machine IN a geolog-
lcal laboratory is, therefore, one at
least capable of cutting small pieces OF
rock substance An explanation is next
In order as to the objects sought to be
accomplished by this machine in It's
scientific uses. The value in lapidary
work will be treated later.
"In the present improved methods
of study in mineralogy and lithology
n O. the study of the composition.
Structure origin and alteration of
rocks), it is essential that very thin
sections shall be made of minerals
and of rock substances, so thin that
most Of the component substances will
he transparent; such sections may be
from 1-15O to 1850 or 1-1000 of an inch
in thinness. By examining such sec
+ions under the compound microscope
one can detect the presence of min
eral species and of phenomena of struc-
ture. not otherwise readily, If at all
recognizable.
'In paleontology the study of an
cient extinct life in the form Of fos
sils). it is often necessary to detect
or ascertain the structure of fossils il
rocks. either by inspection of a cu1
and polished surface or of thin trans,
parent sections for microscopic study