The Roanoke times. [volume] (Roanoke, Va.) 1890-1895, 1890-10-16

stone has been known for many CEN
turtles. 1t was worry early observed that,
by contact with it, iron is maynctizcd;
and it is needless to dwell here upon
tho history allied to this discovery, now
constituting the wonderful science of
magnetism.
Deposits of magnetic ore are distribu-
ted all over the world. The orc is some
times very rich and comparatively free
from ganguc. sometimes spirsely dis
seminated in the native rock. These
bodies of lean ore often cover large
areas. Modern ingenuity has utilized
the principle OF the magnet. originally
derived from the orc itself, and really
belonging to the tins of Plato and
Theophrastus, to separate the magnetic
ore particles from til. rock which has
previously been crushed. This proc ess
RECEIVERS the ore i'll the state of con-
centratc very rich in iron and, in some
cases, desirable for Resscmer purposes.
The magnetic separator is no longer
novelty. 1t was only at the last meet
ing of the Institute in New York, that
Messrs. Birkinbine and Edsion Grams,
xvii, 1881 and Mr.. Robert Cook Ub.,
599) described some Of the principal de-
signs of apparatus in use.
E. S. Dana classifies the natural mag
netic minerals in the following order:
magnetic, pyrrohotite, franklinite, al
mandite and minerals containing con-
siderable Eco" or these. ferroso-ferric
oxide, or magnetic, is the type. The
propOrtionate amount of ferrous oxide
essential to magnetic tho compound, is
not established. Ferrous oxide appears
to he the only magnetic oxide of iron.
Tissandier, (Compt. Rend., lxxiv., 53O
produced ferrous oxide in the anhydrous
state by the action of carbon-dioXide on
pure iron at n red heat, according to the
equation:
CO.-FcO+CO.
This is black, crystalline and mag
netic. Heated to redneSS in the air. it
is converted into Fe sO,.
Sidot (Compt. Rend., xvii, l75) has
also produced an oxide exhibiting mag
netic polarity, by heating ferric oxide to
a temperature not sufficient to fuse it,
in an carthcn tube placed in the mag
netic meridian.
A. Frcnzcl (.Iahrb. f. Min, 1874, p.
6s5) accidentally obtained small rhom
bohedra, slightly magnetic. by igniting
Il precipitatc of fcrric hydrate.
The presence of ferrous oxide in mag
netitc, whether as Il molecular constitu-
ent of the compound, or as an indcpcnd
ent moloculc, seems to communicate the
property of magnetism.
Magnetic oxide of iron, as an artificial
product, is considered to result from the
direct action of carbon dioXidc. In
simple detcrminative blow-pipc work,
the rcducing-flame alone, or with the
aid OF alkaline carbonate, produces mag
nctic particles. or slag-glObulcs, from
nearly all iron-mincrals.
Spathic iron ores have long been
known to exhibit, after roasting. magnet
ic propcrties-largely due, however, to
the presence of metallic PARTICLES i'll the
roasted ore. Carbon dioNide in the ore
is also here considered an important fac
tor. Of such ores. the orc-drcssing at
the zinc works at l'ribranl. bohemia,
described by Mr.. Ellis Clark. il. Grams,
tx, 45l. furnishes an illustration. The
principle is here used for the separation
of iron oXile from zinc -blendc.
'.ThcSc are separated from other ma
terial by tho ordinary conc ,ntration pro-
cesscs, and are then i'll the form of
powder, the grains being less. than
millimetcr in diameter. This powder
is composed Of spathic iron-or, and zinc
blende. and is roasted in Il small oven.
when the ore is rendered sufficiently
magnetic"
1t is then separated by magnetic
separator, and the zinc-blende is thus
recovered.
In nearly all cases of the carbonates
of iron similarly treated, minute glob-
ules or metallic iron are contained i'll
the roasted oxide. Furthermore, the
expulsion of the carbon dioXide con
tanned in the ore. with contact of carbon
at certain heat. approXimatcs to the
conditions of the blast furnace and
favors the reduction of part of the fer
rous oxide to the metallic state. The
roasted carbonate is always strongly
magnetic. I,ut. from the fusible nature
of the ore, it is extremely difficult to
prevent it from melting during the pro-
cess, SO that nearly all the associated
minerals assume the form of ''clinkers"
with the ore. This circumstance, togeth
er with the expense OF crushing tn" ore
sufficiently fine, makes the magnetic sep
aration Of iron oxide from the ganguc ore
unprofi table i'll such cases. AT l'ibram.
zinc -blcndc is sought. and the oxide of
iron is Il secondary product.
ncmatito il sometimes magnetic, and.
according to Dana, even magnc ti-polar
of course. as an incidental occurrence,
other than in crystallzcd specimens.
On account of It's rarity, as well rs the
fecblcncss OF the attraction IL presents
magnetic hcmatite is not available for
practical purposes. Martitc. the iso-
mctic fcrric oxid, which is supposed to
be Il pSeGdOmOrph after nagnetitc Is
attracted by the magnet. The famous
ore from Marquette. in the Lake SUI
perior region, abounds with crystals of
martite. The ore from the Juragua