Scientific American Supplement, No. 430, March 29, 1884

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The general design of the instrument, as shown in a somewhat crude form
when first exhibited, is given in the figure, where A is the magnetizing
coil within which the sample of iron or steel wire to be tested is
placed, B the suspended needle, C the compensating coil, and M the
magnet used as a compensator, having a scale beneath it divided into
quarter degrees.

The idea of employing a magnet as compensator in a magnetic balance is
not new, this disposition having been used by Prof. Von Feilitzsch in
1856 in his researches on the magnetizing influence of the current. In
Von Feilitzsch's balance, however, the compensating magnet was placed
end on to the needle, and its directive action was diminished at will,
not by turning it round on its center, but by shifting it to a greater
distance along a linear scale below it. The form now given by Hughes to
the balance is one of so great compactness and convenience that it
will probably prove a most acceptable addition to the resources of the
physical laboratory.--_Nature_.

* * * * *

HOW TO HARDEN CAST IRON.

Cast iron may be hardened as follows: Heat the iron to a cherry red,
then sprinkle on it cyanide of potassium and heat to a little above red,
then dip. The end of a rod that had been treated in this way could not
be cut with a file. Upon breaking off a piece about one-half an inch
long, it was found that the hardening had penetrated to the interior,
upon which the file made no more impression than upon the surface. The
same salt may be used to caseharden wrought iron.

* * * * *

APPARATUS FOR MEASURING SMALL RESISTANCES.

The accompanying engraving shows a form of Thomson's double bridge, as
modified by Kirchhoff and Hausemann. The chief advantage claimed for
this instrument consists in the fact that all resistances of defective
contact between the piece to be measured and the battery are entirely
eliminated--an object of prime importance in measuring very small
resistances. By the use of this instrument resistances can be measured
accurately down to one-millionth of a Siemens unit.

The general arrangement of the instrument is shown in Fig. 1; Fig. 2
being a diagram of the electrical connections.

[Illustration: FIG. 1.--KIRCHHOFF AND HANSEMANN'S BRIDGE FOR MEASURING
SMALL RESISTANCES.]

The piece of metal to be measured, M, is placed in the measuring forks,
gg, in such a manner that the movable fork is removed as far as possible
from the stationary one; if the weight of the piece be insufficient to
secure a good connection, additional weights may be placed upon it. The
main circuit includes the battery, B (Fig. 2), consisting of from two to
four Bunsen cells, the key, T, the German silver measuring wire, N, and
the piece of metal resting on the forks, all being joined in series. The
German silver wire, N, is traversed by two movable knife-edge contacts,
cc, as shown. Connections are made between these contacts, cc, the
resistance box, the prongs, k and l, of the forks, gg, and the
reflecting galvanometer, as shown in Fig. 2. A resistance of ten units
is inserted at o and n, while at m and p twenty units or one thousand
units are inserted. The positions of cc are then varied until the
galvanometer shows no deflection when the key, T, is depressed.

[Illustration: FIG. 2.--DIAGRAM SHOWING ELECTTRICAL CONNECTIONS OF
BRIDGE.]

When such is the case, the ratio of resistances n/m is equal to o/p;
letting M equal the resistance of the metal bar between the points, h
and i, and N equal to the resistance between the points, cc, on the
measuring wire, N, then we shall have

M = N (n/m) = N (o/p).

Knowing the cross section in millimeters, Q, of the bar, and observing
the temperature, t, in degrees Centigrade, its conductivity, x, as
compared with mercury can be determined. If L be the distance, h l or k
i, in meters, then

x = (1/m) (L/Q) (1 + at).

For pure metals the value of a may be taken at 0.004; but alloys have a
different coefficient. The instrument is made by Siemens and Halske,
and is accompanied by a table giving resistances per millimeter of the
measuring wire, N.--_Zeitsch. fuer Elektrotechnik_.

* * * * *

TERRESTRIAL MAGNETISM.

[Footnote: For a full account of experiments relating to magnetism on
railways in New York city, see SCIENTIFIC AMERICAN, January 19,1884.]

_To the Editor of the Scientific American_:

An item has appeared recently in several papers, stating that New York
is a highly magnetized city--that the elevated railroad, Brooklyn Bridge
cables, etc., are all highly magnetized. As this might convey to the
general reader the impression that the magnetism thus exhibited was
peculiar to New York city, and as many of your subscribers look
anxiously for your answers to numerous questions put for the elucidation
of apparent, scientific mysteries, I have thought that perhaps a
statement in plain language of experiments made at various times, to
elucidate this subject, might, in conjunction with a diagram, serve to
explain even to those who have not made a special study of science a few
of the interesting phenomena connected with

TERRESTRIAL MAGNETISM.

Some of the first experiments I made, while professor at the Indiana
State University, were detailed in the March and August numbers,
1872, of the _Journal_ of the Franklin Institute, and I think showed
conclusively that the earth, by induction, renders all articles of iron,
steel, or tinned iron magnetic; possessing for the time being polarity,
after they have been in a settled position for a short time.

In Dr. I. C. Draper's "Year Book of Nature" for 1873, mention is made
of the experiments in which I found every rail of a N. and S. railroad
exhibiting polarity.

The same statements were repeated in one of a series of articles sent by
me to the _Indianapolis Daily Journal_, dated Jan. 20, 1877, in which I
used the following language:

"Every article of iron or steel or tinned iron, by the earth's
induction, becomes magnetic. Thus, if we examine our stoves, or a
doorlock, or long vertical hinge, or even a high tin cup, by holding a
delicate magnetic needle in the hand near those objects, we find the
earth has, by induction, attracted to the lower end of the stove
utensils, etc., the opposite magnetism from its own; and repelled to the
upper end of the stove, etc., the same magnetism which exists in our
northern hemisphere. Consequently, the bottom of the stove, or of the
hinge, cup, etc., will attract the south (or unmarked end) of our
needle; while the top of the stove, etc., attracts the north, or marked
end of our magnetic needle. If we apply our needle to the T rails of a
N. and S. railroad, we not only find that the lower flange of the rail
attracts the S. end of our needle, while the upper flange attracts the
N. end of our needle, but we also find, where the two rails come nearly
together (say within two inches), that the N. end of the rail attracts
the S. end of our needle, while the S. end of the rail attracts the N.
(or marked) end of our magnetic needle."

[Illustration: MAGNETISM ON RAILWAYS.]

Quite recently, being anxious to see the effect produced on the needle
by rails laid E. and W., I experimented on some recently laid here;
starting from a S. terminus, in the town of New Harmony, and gradually
curving northeast, until the road pursues a due east course to
Evansville. There is, however, a branch road of about half a mile, which
starts from the Wabash River, at a _west_ terminus, and runs due east
to join the other, near where that main track commences its northeast
curve. The results (more readily understood by an inspection of the
diagram) were as follows:

1. At the south terminus of the railroad, the rails on the east side of
the track as well as those on the west side attracted at their south
ends the marked end of a small magnetic needle, both at the upper and
lower flange; the usual vertical induction being in this case overcome
by the greater lateral induction. Whenever, on progressing north, the
rails were at least about two inches apart, the upper flange of the
north end of any rail would attract the unmarked, while the south end
of its neighbor or any other of the north and south laid rails would
attract the marked end.

2. The same results were obtained from rails laid all around the
northeast curve, and even after they had acquired a due west to east
course; showing that each rail acquired the same magnetic polarity which
would be exhibited by any magnetic needle oscillating freely in our
northern hemisphere, dipping also at its north end considerably downward
if suspended at its center of gravity.

3. Applying the needle at the _west_ terminus, a few anomalies were
observed; but, especially nearer the junction, the rails all gave the
normal result found on the main track.

4. The wheels of the cars standing on the north and south track followed
the same law, exhibiting both vertical and lateral induction, so that
the lower rims and the forward or north part of the periphery attracted
the unmarked end of the needle, while the upper and rear, or south
portions of the periphery of the wheel attracted the marked end.

5. The wheels of cars standing on the east and west road exhibited
the following modification. The lowest rim of all the wheels, whether
standing on the _north_ rails or on the _south_ rails of said track,
in consequence of vertical induction attracted the unmarked end of the
needle, and the upper rims attracted the marked end of the needle; but
the middle portions of the periphery, both anterior and posterior, of
the wheels standing on the north rail, attracted the unmarked end, while
similar middle portions of wheels standing on south rails attracted the
marked end; in consequence of horizontal induction, the wheels being
connected by iron axles, and thus presenting considerable extension
_across_ the track, viz., from south to north.

Magnetite seems to have acquired its polarity in the same manner,
namely by the earth's induction, when the ore contains a large enough
percentage of pure iron. A large specimen (6 in. long by 31/2 deep and
weighing 51/2 lb.) which I obtained from near Pilot Knob, Missouri,
exhibits polarity, not only at its lateral ends, but also vertically,
as the lower surface attracts the unmarked end of a needle, while the
plane, which evidently occupied the upper surface in its native bed,
attracts the marked end of the needle.

Iron fences invariably exhibit only the polarity by vertical induction;
so also small buckets, bells, etc. But in the case of a bell about 3 ft.
in diameter at its base, and over two feet deep, tapering to about a
foot in diameter at the top, I found that although the top attracted the
marked end of the needle, the bottom attracted the unmarked end of the
needle only around the northerly half of the circumference, while
the southern portion of this lower rim attracted the marked end in
consequence of lateral induction, as in N. and S. rails.

Thus, upon a comparison of all these facts, it would appear that, if
the magnetism induced by the earth is due to so-called currents of
electricity, those currents must be _underneath_ the rails, and must
move from west to east, under the south to north rails, and from south
to north under the west to east laid rails, as indicated by the arrows
in the diagram.

This accords perfectly with what we should theoretically expect, in our
northern hemisphere, if the electricity in the earth's crust is due to
thermo-electrical currents from east to west, namely, from the more
heated to the less heated portion, on any given latitude, while the
earth revolves from west to east; as well as also from electrical
currents trending from tropical to Arctic regions.

As the network of iron rails spreads from year to year more extensively
over our continent, it will be interesting to observe whether or not
any effect is produced, meteorological, agricultural, etc., by this
diffusion of magnetism.

It may further interest some of your readers to have attention called to
facts indicating

SYNCHRONOUS SEISMOLOGY.

The year recently closed furnishes interesting corroborative testimony
of an apparent law regarding the propagation of earthquake movements
_most readily_ along great circles of our globe, as well as evidence
that these seismic movements are frequently transmitted along belts
(approximating to great circles) coincident sometimes with continental
trends, at other times with fissures which emanate in radii at every
30 deg., around the pole of the land hemisphere in Switzerland, as described
in one of my papers, read at the Montreal meeting of the A.A.A.S.

The terms synchronism or synchronous, as here used, are not designed to
imply absolute simultaneity (although that is sometimes the case with
disturbances 180 deg. apart), but are rather intended to indicate the
tendency presented by these phenomena to exhibit this internal activity,
during successive days, weeks, or even months, along a given great
circle of the earth, especially one or more of those connected with the
land center; perhaps most of all along the great circle which forms the
prime vertical, when the center of land is placed at the zenith.

In order to test the above, let us examine the record of the most
prominent earthquakes or volcanic eruptions for the year 1883.

Late in Dec., 1882, and early in Feb., 1883, shocks occurred in New
Hampshire; on Jan. 11, 1883, also at Cairo, Illinois, and about the same
time at Paducah, Ky.; Feb. 27 at Norwich, Conn., and early in Feb. at
Murcia, Spain.

These, by examination of any good globe, will be found on a belt forming
one and the same great circle of the earth.

Late in March and during part of April the volcano of Ometeke in Lake
Nicaragua was active (after being long dormant); Panama, portions of
the U.S. of Colombia, and of Chili; also, in May, Helena, M.T.; and,
in June, Quito (with Cotopaxi active) were all more or less shaken by
earthquakes; and are all found on one belt of a great circle.

The principal record for the remainder of the year comprised:

An earthquake at Tabreez in North Persia, early in May, 1883.

The awful destruction in Ischia, July 29 (with Vesuvius active).

The fearful eruption in the Straits of Sunda, 25th Aug. and later.

Shocks in Sumatra and at Guayaquil, about same date or early in Sept.

Shocks at Dusseldorf, according to a Berlin paper of 5th Sept.

Shocks at Santa Barbara and Los Angeles, early in Sept.

Shocks at Gibraltar and Anatolia in October.

Shocks at Malta, Trieste, and Asia Minor in October.

Azram shaken late in Sept., and great destruction between Scios and
Smyrna.

Lastly, the formation of a new island in the Aleutian Archipelago. Date
of outburst, early in October, 1883.

Besides these, there were several other less severe disturbances, the
records of which are chiefly obtained from Nature, and which will-be
referred to below.

If the globe be so placed as to have the land center at the zenith, the
exact position of the new island, near Unnok, will be found under the
brazen meridian, while Agram, Tabreez, Sunda, Sumatra, Quito, and
Guayaquil are all on the prime vertical.

Vesuvius and Hecla were both active early in the year, and they, with
the ever restless Stromboli, are situated on the great circle which
forms with the land center at Mount Rosa, the radius running S. 30 deg. E.,
and which would embrace the chief disturbances up to the middle of the
year, including as we go north Malta, Sicily, Rome, region of the Po,
Bologna, and in the Western Continent, after passing Hecla, Helena in
Montana Territory, reaching in Washington Territory and Oregon the belt
of it. American volcanoes: Mounts Baker, Rainier, St. Helens, Hood, and
Shasta.

Still another seismic belt, starting from the ever active Fogo, and
passing through Teneriffe (at that time erupted), would include the
regions disturbed in Oct. and Nov., namely, Cadiz, Gibraltar, Malaga
(Murcia and Valencia somewhat earlier); it then traversed the center of
land, caused the earthquakes at Olmutz in Moravia, and even tremors felt
at Irkutsk, as the seismic war moved along said great circle to the
volcanic region of S. Japan.

Again, the belt which covers the meridian of land center (about 8 deg.-10 deg.
E. long) covers also the region of a disturbanced area in Norway, as
well as that portion of Algeria, viz., Bona, in which a mountain 800
meters high, Naiba, is gradually sinking out of sight. About 100 geo.
miles E. of Bona is where Graham's Island appeared in the Mediterranean,
and a few months later disappeared in deep water.

Another highly seismic belt extends from the volcanoes of Bourbon, N.
Madagascar, and Abyssinia to Santoria and the oft disturbed Scios,
Smyrna, and Anatolia region; and along the same great circle were shaken
Patra in Greece on the 14th Nov., and Bosnia on the 15th; while shocks
had been felt at Trieste and Muelhouse about the 11th, and at Styria on
the 7th, and disturbances at Dusseldorf in Sept. Finally, on the 28th
Dec. S. Hungary (near the confluence of the Drave with the Danube) was
visited by seismic movements along this same great circle, which passes
through the extinct volcanic region of the Eifel, the oft shaken Comrie
in Perthshire, Scotland, the volcanic Iceland, our National Park with
its thousands of geysers, the cataclysmic region of Salt Lake and the
Wahsatch Mountains (so graphically described by the geologists of the
U.S. Geol. Survey), giving rise in Sept. to the earthquakes of Los
Angeles and Santa Barbara, and finally reaching the volcanic islands of
the Marquesas group.

Thus the seismic efforts of 1883 may be seen to have expended their
force partly along the great backbone of the S. and N. American
Cordillera, but more especially from the center of land E. and W. along
its prime vertical from Sunda to Quito, also southwesterly by the E.
coast of Spain, as well as due S. through Algeria, and S. 30 deg. E. through
Rome, Naples, Sicily, etc. Finally, the autumnal catastrophes at and
near Scios, Anatolia, etc., seem to have been caused by a seismic wave,
propagated along the great circle, which often agitates Janina, and
produces earthquakes at Agram, where this great circle crosses the prime
vertical.

RICHARD OWEN.

New Harmony, Ind., 27 Feb., 1884.

* * * * *

THE IRON INDUSTRY IN BRAZIL

(PROVINCE OF MINAS GERAES.)

By Prof. P. FERRAND.

Up to the present time, the methods employed in the province of Minas
Geraes (Brazil) for obtaining iron permit of manufacturing it direct
from the ore without the intervening process of casting. These methods
are two in number:

1. The _method by cadinhes_ (crucibles), which is the simpler and
requires but little manipulation, but permits of the production of but a
small quantity of metal at a time.

2. The _Italian method_, a variation of the Catalan, which requires
more skill on the part of the workmen and yields more iron than the
preceding.

As these methods seem to me of interest, from the standpoint of their
simplicity and easy installation, I propose to describe them briefly, in
order to give as faithful and general an _apercu_ as possible of their
application. At present I shall deal with the first one only, the one
called the method by _Cadinhes_.

STUDY OF THE METHOD BY CADINHES.

The province of Minas Geraes ocupies a vast extent in the empire
of Brazil, its superficies being about 900,000 square kilometers,
representing nearly a third of the total surface.

The population is relatively small and is disseminated throughout a much
broken country, where the means of communication are very few. So it is
necessary to succeed in producing what iron is needed by means that are
simple and that require but quickly erected works built of such material
as may be at hand. The iron ore is found in very great abundance in this
region and is very easily mined.

In the center of a mass of quartzites that seem lo constitute the upper
level of the eruptive grounds of the province, there are found strata of
an ore of iron designated as _itabirite_--a mixture of oxide of iron and
quartz. These strata are of great thickness, and have numerous outcrops
that permit of their being worked by quarrying.

These itabirites present themselves under two very distinct aspects and
offer a certain difference in their composition. Some are essentially
friable, and are called by the vulgar name of _jacutingaes_. It is
this variety (which is the one most easily mined) that is principally
consumed in the forges. The others, on the contrary, are compact.
Their exploitation is more difficult, and before putting them into the
furnaces it is necessary to submit them to breakage and screening; so
the use of them is more limited.

The first variety contains less iron and more gangue, but, _per contra_,
possesses much oxide of manganese. The second, on the contrary, is
formed almost wholly of oxide of iron with but little gangue and only
traces of oxide of manganese. The following are analyses of these two
varieties of ore:

_Friable Ore_.

Fe_{2}O_{2}.................................. 84.9
Oxide of manganese........................... 9.2
Water........................................ 1.9
Quartz....................................... 4.1
----
100.1

_Compact Ore_.

Fe_{2}O_{3} and traces of manganese.......... 99.6
Quartz....................................... 1.1
----
100.7

_Situation of the Forges_.--A forge is usually placed on the bank of
a brook, or rather of a torrent, which supplies the fall of water
necessary for the motive power by means of a flume about a hundred
meters in length. In most cases the forge is surrounded on all sides
with a forest which yields the wood necessary for the manufacture of the
charcoal, and is in the vicinity of the iron quarry, so as to reduce the
expense of hauling the ore as much as possible. The neighboring
rocks furnish the foundation stones and stones for the furnaces; the
decomposed schist gives the cement and refractory coating, and the
forest provides the wood necessary for the construction of the road,
sheds, etc. The head of the trip hammer, the anvils, and the tools are
the only objects that it is necessary to procure, and even these
the master of the forge often manufactures in part, after beginning
production with an incomplete set.

[Illustration: 7a FIG 1.--FOUR-CRUCIBLE FURNACE AND FORGE; (PLAN).]

_General Arrangement of a Forge_.--A forge usually consists of one or
two furnaces of three or four crucibles (the one shown in plan in Fig.
1 has only one four crucible furnace, A); 1 or 2 two fire reheating
furnaces, B; 1 trip hammer, C, actuated by a hydraulic wheel, D;
2 tromps which drive the wind, one of them, E, into the cadinhes
(crucibles), and the other, F, into the reheating furnace; 2 anvils,
G and H, placed near the furnace, for working delicate pieces; and
finally, the different tools that serve for maneuvering the bloom and
finishing the bars. The charcoal is preserved from rain under a shed, l.
The ore, which is brought in as needed, is dumped in a pile at M, in
the vicinity of the crucibles. The buildings are set back against the
mountain, and the water is led in by a double flume, L and N, made of
planks, and empties on one side into the wheel and into the tromp, F,
and on the other into the tromp, E, and then runs into a double waste
channel, P and Q, which carries it to the stream.

[Illustration: FIG 2.--FOUR-CRUCIBLE FURNACE; (PLAN).]

_Four Crucible Furnace_ (Fig. 2).--The arrangement of a furnace is very
simple. It consists of a cube of masonry containing several cylindrical
apertures with elliptic bases, whose large axis is paralleled with the
smaller side of the masonry. This form recalls that of a crucible;
and these cavities are, moreover, so named. In the front part of each
cadinhe there is a rectangular aperture that gives access to the bottom
of the crucible and facilitates the removal of the bloom therefrom. At
the back part there is a small aperture for the introduction of the
tuyere, and which permits, besides, of the nozzle of the latter being
easily got at so as to see whether the blast is working properly.

The sides of the crucibles are covered with a thin layer of refractory
clay, and their bottoms have a spherical concavity to hold the bloom.
The tuyere, which is fitted to a wooden conduit of square section
that runs along the back of the masonry, is placed in the axis of the
cadinhes and enters the masonry at a few centimeters from the bottom
in such away that its nozzle comes just flush with the surface of the
refractory lining. This arrangement prevents the tuyere from getting
befouled by scoriae during the operation of the furnace and thus
interfering with the wind.

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