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

V >> Various >> Scientific American Supplement, No. 430, March 29, 1884

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_Tromp_.--The tromp which furnishes the necessary wind to the cadinhes
consists of a hollow wooden conduit, a (Fig. 3), of square section,
which enters a chamber, b, along a length of 0.1 m. This conduit, which
is about 7 meters in height, receives the water from the flume through
the intermedium of an ajutage of pyramidal form, which serves to choke
the vein of liquid, and the extremity of which is at a few centimeters
from the conduit in order to facilitate the entrance of the air; the
latter being attracted by an ill defined action that is supposed to
be due to its being carried along by the water, and to a depression
produced by choking the flow of the liquid.

[Illustration: FIG. 3.--THE TROMP.]

Since the air that is sucked in during the operation has constantly same
pressure, there is no valve for regulating the entrance of the water
into the vertical conduit. Upon issuing from the latter, the mixture of
air and water strikes the surface of the water in the chamber, b,
and the violence of the shock upon the bottom is deadened by the
interposition of a stone. While the water is escaping through a lateral
aperture in the chamber, b, the air is reaching the tuyeres through a
wooden conduit of square section which is fitted to an aperture in the
upper part of the chamber. This sorry arrangement, which obliges the
mixture of air and water to penetrate the water at the bottom of the
upright conduit, a, retards the separation of the two fluids, and
results in damp air being forced into the crucibles.

_The Trip Hammer_.--Fig. 4 shows the general arrangement of the
apparatus that go to make up the forging mill. The hammer and cam shaft
have their axes parallel, and the latter is placed in the prolongation
of the axis of the wheel. The hammer consists of a roughly squared beam,
4 meters in length, and of 0.25 m. section. The head, A, consists of a
mass of iron weighing 150 kilos, including the weight of the straps
that surround the beam on every side of the piece of iron. The axis of
rotation is situated at the other extremity of the beam, B. The cam
shaft which serves to maneuver the trip hammer is provided with four
cams which lift the beam at a point near the hammer. The length of this
shaft (to the extremity of which is adapted the water wheel) is 4.75 m.,
and its diameter is 0.50 m. The wheel is an _overshot_ one, 3.25 m. in
diameter by 1 m. in width. The water, which is led to it by a flume,
acts upon it by its weight and impact, and is retained in the buckets
and kept from overshooting the mark by a jacket made of planks.

[Illustration: FIG. 4.--THE TRIP HAMMER.]

The anvil upon which the hammer strikes is surrounded by a bed of stones
(quartzites) derived from the neighboring rocks. It is a mass of iron,
75 kilogrammes in weight. In order to prevent vibrations in the trip
hammer when it is lifted, and increase the number of blows, there is
established a spring beam, which is formed of unsquared timber, which
is firmly fastened at one of its extremities, and which receives at the
other end the shock of the hammer head when the latter reaches the end
of its upward travel.

_Reheating Furnace_.--This is a double fire furnace, like those used in
our smithies, except that the wind, instead of being forced into it by
means of a bellows, is supplied by a tromp which receives water from the
same channel as the wheel. The two furnace tuyeres are arranged exactly
like those of the cadinhes, upon a wooden conduit which starts from the
wind chamber (Fig. 5). This furnace serves to prevent the cooling of
such blooms as are awaiting their turn to be shingled, and of such bars
of finished iron as are being made into tools.

OPERATION OF THE SYSTEM.

A forge like the one whose plan we give, may be run with 1 workman at
the cadinhes, 1 assistant, 1 workman at the hammer; total, 3 men.

_Furnace_.--The work lasts about twelve hours per day, and three
operations of three to four hours are performed in each cadinhe, thus
making twelve per day. At each operation, 22.5 kilos. of ore and 45 of
charcoal are used. From this there is obtained a bloom of 15 kilos. The
operation is performed as follows:

While the assistant has gone to put the bloom of the preceding operation
under the hammer, the workman prepares at the bottom of the crucible a
bed consisting of a mixture of sand and very fine charcoal, and then
fills the crucible up to its edge with charcoal. At the end of a quarter
of an hour, the fuel being thoroughly aglow, the workman puts in the
first charge of ore in powder (_jacutingue_), about 2 kilos, and covers
it with charcoal.

Starting from this moment, he goes on charging every five or ten minutes
with 1.5 to 2 kilos of ore, taking care in doing so to keep the crucible
stuffed with charcoal, which the assistant places in piles around each
cadinhe. This lasts about two and one-half hours. At the end of this
time he stops putting in charcoal, and standing upon the masonry, walks
from one cadinhe to another, carrying a large rod, in order to study the
lay of the bloom. Then, the fire being entirely out, he scrapes out the
bed of sand and charcoal that closes the opening in the bottom of the
crucible, removes the mass of ferruginous scoriae which forms a hard
paste and surrounds the bloom, and takes this latter out by means of a
hook.

The workman runs the four cadinhes at once, this being easily enough
done, since he has neither to bother himself with regulating the wind,
which enters always with the same pressure, nor with the flow of the
scoriae, which remain always at the bottom of the crucible. His role
consists simply in keeping his fires running properly, being guided in
this by the color of the flame without making an examination in the
interior. He draws each of the four blooms out from its bed at the end
of the operation, while the assistant carries the first to the hammer
and the three others to the reheating furnace. He afterward cleans
out the crucible, prepares the bed of sand and charcoal, fills with
charcoal, and then passes to the next, and so on.

[Illustration: FIG. 5.--REHEATING FURNACE.]

_Trip Hammer_.--The workman at the hammer takes the bloom from the hands
of the assistant and shingles it under the head. Then he begins to give
it shape, bringing it to the state shown at c, in Fig. 7. The assistant
then brings him another bloom and takes the one that has been shingled
to the reheating furnace, where he heats but one of its extremities.
When the four blooms have been shingled, the workman takes up the first
and begins to draw out one of its extremities, which he afterward cools
in water and uses as a handle for finishing the work, d. Then he reheats
the other extremity, and, after drawing it out as he did the other,
obtains a bar of finished iron which he doubles, as shown at e, to thus
deliver to the trade.

[Illustration: FIG. 6.--CADINHE IN OPERATION.]

One of these bars weighs from 11 to 12 kilogrammes. It will be seen
that, during the course of the work, the furnace workmen and the hammer
workmen have well defined duties to perform; but it is not the same with
the assistant, who goes from one to the other according to requirements.
There are, however, some forges in which each of the workmen has an
assistant, since the blooms produced are heavier, and one assistant
would not suffice for the work of the two men. In such a case the
assistant at the crucibles carries the blooms to the reheating furnace,
and the assistant at the hammer carries them from thence to the hammer.

[Illustration: FIG. 7.--WORKING THE BLOOM.]

ELABORATION OF THE ORE.

We have seen that the workman who has charge of the fire contents
himself with putting charcoal and ore alternately into the crucibles,
and that too according to the aspect of the flames, without making any
examination in the interior, in order to judge whether the work is
proceeding well. The bloom forms gradually beneath the nozzle of the
tuyere, in the center of the bed of sand and charcoal, and is surrounded
on every side with an exceedingly pasty mass, formed of silicates of
iron and manganese (Fig. 7). It is only at the end of the operation that
the workman, by means of a rod, causes the burning coal to drop and
verifies the proper position of the bloom by breaking the layer of
scoriae that surrounds it. This coating he breaks off, removes the bloom
with a hook, and agglutinates with his rod the different bubbles that it
exhibits, and the assistant then carries it to the hammer.

SETTING UP A FORGE.--SELLING PRICE OF THE IRON.

To set up a forge like the one we have described, it is necessary to
count upon a first cost of about 10,000 francs. Add to this the cost of
50 hectares of forest to furnish the charcoal that the workmen have to
make every day. The cost of this is very variable, and floats between
2,500 and 5,000 francs per 100 hectares. The cost the ore is only that
connected with getting it but and hauling it.

_Manual Labor_.--The charcoal burners receive 1.25 francs per load of 90
kilos, thus bringing the price of the product (including cost price of
forest) at 2.4 francs per 100 kilos. The workmen in the furnace are paid
at the rate of from 2.50 to 3.75 francs per day. Those that work the
hammers receive 3.75 francs, and the assistants 1.25 francs.

_Carriage of the Forged Iron_.--The iron is carried from the forge
to the places of consumption on the backs of mules, and the cost of
carriage is, on an average, 0.25 franc per 100 kilos and per kilometer.

_Selling Price_.--The selling price is very variable, and depends
principally upon the distance of the place where sold from the different
forges that surround it. At Ouro Preto the price varies between 45 and
50 francs per 100 kilos.

The following is a _resume_ of the data which precede:

Cost of first establishment.................. 10,000 fr.
Charcoal per kilogramme...................... 2.40
{ Furnace men.... 2.50 to 3.75
Manual labor per day { Hammer men............. 3.75
{ Assistants............. 1.25
Carriage of forged iron per kilometric ton..... 2.50
Selling price per 100 kilos................ 45 to 50

--_Le Genie Civil_.

* * * * *

THE STEAMER CHURCHILL.

We give engravings of the Churchill, a vessel lately built to the order
of Mr. Walter Peace, London agent to the Natal Harbor Board, by Messrs.
Hall, Russell, and Co., Aberdeen. She was designed by Mr. J.F. Flannery,
consulting engineer to the Board, for special service at Natal. The
Churchill has been constructed so as to be capable of towing into or out
of harbor over the bar in any weather, of acting as a very powerful fire
engine, of carrying a large amount of fresh water for the use of other
ships, of landing troops from transports which the harbor is too shallow
to admit, of recovering lost anchors and cables, of which there are a
large number off the coast, and of acting in time of need as a torpedo
or coast defense vessel; she was launched on the 16th August, and is
likely to fulfill all these requirements.

[Illustration: THE NEW STEAMSHIP CHURCHILL.]

The principal dimensions of the vessel are: Length between
perpendiculars 115 feet, breadth, extreme, 22 feet, depth of hold 11
feet, and maximum draught with full bunkers 7 feet 6 inches. There are
four water-tight iron bulkheads forming five compartments; the stern is
built very full to protect the propellers. Accommodation is arranged on
deck for the captain aft with two spare berths, mate and two engineers
amidships, while six white hands will occupy the forward forecastle, and
six Kaffirs the after one. For towing purposes she is fitted with one
main and two skip hooks secured to the main framing; towing rails are
placed aft, while bitts are put on one each quarter, will be seen by
referring to the deck plan.

The vessel is propelled by twin screws 6 feet 8 inches in diameter and
13 feet 6 inches pitch; these are of cast iron, have four blades, and
are driven by a double pair of compound inverted direct acting engines
(see Figs. 4 to 7) which are capable of developing 600 indicated horse
power, and whose cylinders are 19 inches and 34 inches in diameter with
a stroke of 2 feet. The condensers form part of the engine frame, and
have guide faces cast on for the crosshead shoes. They are fitted with
gun metal tube-plates, and each contain 516 tubes, 3/4 inch in diameter,
which have an exposed length of 6 feet 5 inches, and give a total
cooling surface of 650 square feet. The air and circulating pumps are
bolted to the back of the condensers, and are worked by levers from the
engine crosshead. Each engine has one feed and one bilge pump attached
to the air pump, and worked by the same lever. The plan of the engines
shows the pump arrangement very completely.

[Illustration: ENGINES AND BOILERS OF THE NEW STEAMSHIP CHURCHILL.]

The steam is supplied by two circular return tube boilers, 9 feet 6
inches in diameter and 10 feet long, with two furnaces in each. The
boilers, which are of steel throughout, except the tubes, are placed
longitudinally, and are fitted with two pairs of the Martyn-Roberts
patent safety valves. They have one steam dome between them. The total
heating surface is 1,700 square feet, the total steam space is 330 cubic
feet, and the working pressure 100 lb. per square inch.

The fire pump is a Wilson's "Excelsior," with 10 inch steam cylinder and
8 inch water barrel. This powerful pump is in a special compartment of
the fore hold, and will draw water from the bilge, sea, or either hold.
A steam windlass and a double-handle winch are on deck as shown. On
trial trip the engines of the Churchill indicated a maximum of 645.5
horse power, driving the vessel 10.495 knots per hour. The vessel is
remarkable for diversity of uses, for heavy engine power in a small
hull, and for general compactness of arrangement.--_Engineering_.

* * * * *

THREE-WAY TUNNELS.

Mr. T.R. Cramton, who at the Southampton meeting of the British
Association suggested a method of tunneling which, under certain
conditions, seems of excellent promise, brought forward a suggestion at
Southport for the construction of three-way tunnels. Now, the undoubted
aim of all engineers is economy of construction and the securing of
permanent advantages. Mr. Crampton maintains that the suggested system
will give these, that three tunnels of, say, 17 ft. diameter, can be
constructed cheaper than one of 30 ft. diameter. After describing Sir J.
C. Hawkshaw's scheme for the ventilation of long tunnels, the three-way
scheme was discussed. Three separate tunnels of 17 ft. diameter each,
or 227 ft. area, are to be connected by large passages about midway
of their length. These passages are without valves; in fact, free air
passages. Between these midway connections and the ends, say again
midway between, is formed a branch at right angles either above or below
with separate openings from the branch into the other tunnels, such
openings being provided with doors or valves quite clear of the main
tunnel, any two of which may be closed, thus separating at this point
the corresponding tunnels from the third. The branch is to be led to any
convenient position where the exhustion apparatus can be placed. If two
of the tunnels are left open to this branch, and the third one shut off
from it by closing the doors, the vitiated air will be drawn from the
two working tunnels, through the connecting branch, while fresh air will
be partly sucked down the vertical shafts through their open ends and
partly at the center tunnel, which is supplied by forcing air down the
vertical shaft in communication with it, a stop or door being placed
just outside of the bottom of the shaft so as to compel the air to flow
to the center of the tunnel. It will be observed that no trains are
running in this air tunnel so long as it is so used; there are similar
doors for the working tunnel, but they are kept open, unless either of
them is required to be made into an air tunnel, so that the passing
trains run no risk of running into the doors. By means of the doors
above mentioned, any one of the three tunnels can be used as a fresh-air
tunnel, in which the men doing the repairs to the road would be clear of
the traffic, while the other two are used for the traffic, as well as
outlets for the mixed impure gas and air. If a breakdown of a train
occurs in any one tunnel, that tunnel can at once be converted into a
fresh-air one, while its traffic is transferred to the one previously
used for air, thereby avoiding delay. The system described for splitting
the air and drawing off the noxious gases is very similar to that
described by Mr. Hawkshaw at Southampton. The valves and other details
being added, to make the system applicable to three tunnels, it will
be obvious that other modes of ventilation may be adopted. In order to
reduce the number of men working in the tunnel it is proposed, if found
practicable, not to adopt the ordinary ballast and cross sleepers, but
to substitute the longitudinal timber system, the timbers to be secured
to brickwork or concrete, forming a part of the tunnel lining, placing
efficient elastic material between the foundation and longitudinals for
their whole area, also between the rails and sleepers. An open drain is
formed between the rails; by this plan any water accumulating flows over
smooth surfaces through small channels into a drain, the tunnel on each
side being dry. The saving of labor in repairs, if this system can be
employed, is so evident that a large amount of money might be expended
in endeavoring to discover a suitable elastic material for the purpose.
There are data on many long viaducts sufficient to justify experiments
being made on the subject, and it is not unreasonable to expect that
suitable material may be met with. In very long tunnels nothing should
be omitted tending to reduce the number of men working in them. The
opinion was expressed that in tunnels passing through solid materials,
and proper foundations being made for the longitudinals to rest upon,
with good elastic material placed between the rails and sleepers and
foundations, one-half of the men employed on the ordinary cross sleeper
road resting on ballast would be saved, more particularly as the repairs
are effected in pure air free from the traffic as explained. The
estimate as to the cost of this system was upon the dimensions given by
Sir J. Hawkshaw, and the following gives the comparison:

The quantity of excavation and brickwork or concrete in each case will
be as follows: Single tunnel: 30 ft. diameter lining, 3 ft. thick, with
the brickwork forming the air passage = to 36.5 cubic yards per yard
forward. Excavation to outside of brickwork 36 ft. diameter = to 113
cubic yards per yard forward. Three tunnels 17 ft. diameter and 18 in.
brickwork. Brickwork lining for three tunnels = 24.5 cubic yards per
yard forward. Excavation outside brickwork for the same 105 cubic yards
per yard forward. It is assumed that three 17 ft. tunnels are stronger,
more conveniently formed, and involve less risks in construction than
one of 30 ft. diameter; at the same time there is no difficulty in
making the latter. The above shows the saving in the three tunnels of
23 per cent. in brickwork, and about 7 per cent. of earthwork, compared
with one of 30 ft. With regard to ventilation, it is well known that the
power required to force air along passages is practically as the cube of
the velocity; and as the area of the air passages in the single tunnel
is 106 ft. with speed ten miles per hour, and that of one of the 17 ft.
diameter is 227 ft., or rather more than double, giving only five miles
per hour velocity, it follows that the power for this portion would be
eight times less. That for the working tunnels would be practically the
same, the velocities being nearly alike in both cases, which would be
about 21/2 miles per hour--the 30 ft. having an area of 470 ft., the
two single ones together about 450 ft. Upon the face of it the system
deserves a trial. A full consideration of the scheme by engineers
preparing plans for new tunnels would no doubt throw further light
upon the subject and be of interest wherever such work is
contemplated.--_Contract Journal_.

* * * * *

MONT ST. MICHEL.

Every one who has the slightest regard for historical monuments, who
values mediaeval architecture, or cares in the least degree for the
beautiful and the picturesque, must heartily sympathize with M. Victor
Hugo in his protest against the proposed scheme for uniting the
wonderful island of Mont St. Michel with the mainland by means of a
_causeway_, and possibly a _railway_!

Those who know Mont St. Michel well, and, like the writer, have spent
several days upon the island, cannot but feel that such a scheme would
not only be a frightful disfigurement, but would entirely destroy all
the associations and the poetry of the place. Practical people will
say, "Modern improvement cannot stop in its march forward to consider
poetical associations and mere artistic whims and fancies." Now, this
would be a possible argument if Mont St. Michel were a busy, thriving
town, a commercial port, or the seat of great industries; but in a case
where the only trade is that of touting, the only visitors sightseers,
the only "stock-in-trade" mediaeval remains, surely, from a practical
point of view, anything which will injure these antiquities will really
destroy the importance of the island, as its _only_ value consists in
its wonderful historic and artistic associations.

[Illustration: MONT ST. MICHEL, NORMANDY.]

The first glimpse of Mont St. Michel is strange and weird in the
extreme. A vast ghostlike object of a very pale pinkish hue suddenly
rises out of the bay, and one's first impression is that one has been
reading the "Arabian Nights," and that here is one of those fairy
palaces which will fly off, or gradually fade away, or sink bodily
through the water. Its solemn isolation, its unearthly color, and its
flamelike outline fill the mind with astonishment.

Mont St. Michel is by far the most perfect example of a mediaeval
fortified abbey in existence, with its surrounding town and
dependencies, all quite perfect; just, in fact, as if time had stood
still with them since the fifteenth century. The great granite rock
rises to the height of two hundred and thirty feet out of the bay; it
is twice an island and twice a peninsula in the course of twenty-four
hours. The only approach is at low water, by driving or walking across
the sands. When, however, one arrives within a few yards of the solitary
gate to the "town," walking or driving has to be abandoned, and here
the commercial industries of the inhabitants commence. A number of
individuals, half sailors and half fishermen, are standing ready to
carry you on their shoulders over the small gully, which is very rarely
quite dry. Entering through the old gate one sees two ancient pieces
of cannon taken from the English, who unsuccessfully laid siege to the
place in 1422. Close to the gate are the two rival inns, which are very
primitive in their arrangement, the entrance hall forming the kitchen,
as in many old Breton houses. A second frowning old gateway leads to the
single street, which, passing between two rows of antique gabled houses,
and under the chancel of the little parish church, conducts one to the
almost interminable flight of stone steps leading to the gateway of
the monastery. Upon ringing the bell a polite lay brother opens the
iron-studded door, and we are admitted into a solemn, vaulted hall, with
another stone staircase opposite. Here we go up and up, to a second
vaulted hall, where, in olden times, we should have had to give up any
arms which we were carrying. Then another stone staircase, which lands
us in a small court with a well in it, at the opposite end of which is a
heavy and solid arched doorway. We pass through this, expecting to find
ourselves on the top of the central tower of the church at least, and
are surprised to find ourselves in the solemn and almost dark crypt of
the church. Here we have climbed up some 230 feet above the world and
the sea to find ourselves in an underground vault; up in the air and
down under the rock at the same time. Wonderfully beautiful is this
strange crypt, when one's eye gets accustomed to the gloom, with its
exquisite ribbed and vaulted roof, supported upon huge circular columns.
Returning to the court, another doorway conducts us into a most superb
Gothic hall, with a row of slender columns down the center. This was the
monks' refectory in ancient times; adjoining this is another grand hall,
divided into four aisles by rows of granite columns, all of the most
perfect thirteenth century work. Above these are two other halls, still
more magnificent than those below. One of these, called the "Salle des
Chevaliers," is probably the most beautiful Gothic hall in existence.
Again a flight of stone stairs, and we find ourselves, where we should
certainly not have expected, in the cloisters of the monastery, the
exquisite architecture of which, with its countless marble columns and
delicate double arcades, cannot be described.

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