METALLURGY.
“Nigh on the plain, in many cells prepared,
That underneath had veins of liquid fire
Sluiced from the lake, a second multitude
With wondrous art founded the massy ore;
Severing each kind, and scumm’d the bullion dross;
A third as soon had formed within the ground
A various mould, and from the boiling cells
By strange conveyance fill’d each hollow nook;
As in an organ, from one blast of wind,
To many a row of pipes the sound board breathes.”
--_Paradise Lost._
Ever since those perished races of men who left no other record but that
engraven in rude emblems on the rocks, or no other signs of their
existence but in the broken tools found buried deep among the solid
leaves of the crusted earth, ever since Tubal Cain became “an instructor
of every artificer in brass and iron,” the art of smelting has been
known. The stone age flourished with implements furnished ready-made by
nature, or needing little shaping for their use, but the ages of metal
which followed required the aid of fire directed by the hand of man to
provide the tool of iron or bronze.
The Greeks claimed that the discovery of iron was theirs, and was made
at the burning of a forest on the mountains of Ida in Crete, about 1500
B. C., when the ore contained in the rocks or soil on which the forest
stood was melted, cleansed of its impurities, and then collected and
hammered. Archeologists have deprived the Greeks of this gift, and
carried back its origin to remoter ages and localities.
Man first discovered by observation or accident that certain stones were
melted or softened by fire, and that the product could be hammered and
shaped. They learned by experience that the melting could be done more
effectually when the fuel and the ore were mixed and enclosed by a wall
of stone; that the fire and heat could be alone started and maintained
by blowing air into the fuel--and they constructed a rude bellows for
this purpose. Finding that the melted metal sank through the mass of
consumed fuel, they constructed a stone hearth on which to receive it.
Thus were the first crude furnace and hearth invented.
As to gold, silver and lead, they doubtless were found first in their
native state and mixed with other ores and were hammered into the
desired shapes with the hardest stone implements.
That copper and tin combined would make bronze was a more complex
proceeding and probably followed instead of preceding, as has sometimes
been alleged, the making of iron tools. That bronze relics were found
apparently of anterior manufacture to any made of iron, was doubtless
due to the destruction of the iron by that great consumer--oxygen.
What was very anciently called “brass” was no doubt gold-coloured
copper; for what is modernly known as brass was not made until after the
discovery of zinc in the 16th century and its combination with copper.
Among the “lost arts” re-discovered in later ages are those which
supplied the earliest cities with ornamented vessels of gold and copper,
swords of steel that bent and sprung like whalebones, castings that had
known no tool to shape their contour and embellishments, and monuments
and tablets of steel and brass which excite the wonder and admiration of
the best “artificers in brass and iron” of the present day.
To understand and appreciate the advancements that have been made in
metallurgy in the nineteenth century, it is necessary to know, in
outline at least, what before had been developed.
The earliest form of a smelting furnace of historic days, such as used
by the ancient Egyptians, Hebrews, and probably by the Hindoos and other
ancient peoples, and still used in Asia, is thus described by Dr. Ure:
“The furnace or bloomary in which the ore is smelted is from 4 to 5 feet
high; it is somewhat pear-shaped, being about 5 feet wide at bottom and
1 at top. It is built entirely of clay. There is an opening in front
about a foot or more in height which is filled with clay at the
commencement, and broken down at the end of each smelting operation. The
bellows are usually made of two goatskins with bamboo nozzles, which are
inserted into tubes of clay that pass into the furnace. The furnace is
filled with charcoal, and a lighted coal being introduced before the
nozzle, the mass in the interior is soon kindled. As soon as this is
accomplished, a small portion of the ore previously moistened with water
to prevent it from running through the charcoal, but without any flux
whatever, is laid on top of the coals, and covered with charcoal to fill
up the furnace. In this manner ore and fuel are supplied and the bellows
urged for three or four hours. When the process is stopped and the
temporary wall in front broken down the bloom is removed with a pair of
tongs from the bottom of the furnace.”
This smelting was then followed by hammering to further separate the
slag, and probably after a reheating to increase the malleability.
It will be noticed that in this earliest process pure carbon was used as
a fuel, and a blast of air to keep the fire at a great heat was
employed. To what extent this carbon and air blast, and the mixing and
remixing with other ingredients, and reheating and rehammering, may have
been employed in various instances to modify the conditions and render
the metal malleable and more or less like modern steel, is not known,
but that an excellent quality of iron resembling modern steel was often
produced by this simple mode of manufacture by different peoples, is
undoubtedly the fact. Steel after all is iron with a little more carbon
in it than in the usual iron in the smelting furnace, to render it
harder, and a little less carbon than in cast or moulded iron to render
it malleable, and in both conditions was produced from time immemorial,
either by accident or design.
It was with such a furnace probably that India produced her keen-edged
weapons that would cut a web of gossamer, and Damascus its flashing
blades--the synonym of elastic strength.
Africa, when its most barbarous tribes were first discovered, was making
various useful articles of iron. Its earliest modes of manufacture were
doubtless still followed when Dr. Livingstone explored the interior, as
they now also are. He thus describes their furnaces and iron: “At every
third or fourth village (in the regions near Lake Nyassa) we saw a
kiln-looking structure, about 6 feet high and 2½ feet in diameter. It
is a clay fire-hardened furnace for smelting iron. No flux is used,
whether with specular iron, the yellow hematite, or magnetic ore, and
yet capital metal is produced. Native manufactured iron is so good that
the natives declare English iron “rotten” in comparison, and specimens
of African hoes were pronounced at Birmingham nearly equal to the best
Swedish iron.” The natives of India, the Hottentots, the early Britons,
the Chinese, the savages of North and South America, as discovery or
research brought their labours to light, or uncovered the monuments of
their earliest life, were shown to be acquainted with similar simple
forms of smelting furnaces.
Early Spain produced a furnace which was adopted by the whole of Europe
as fast as it became known. It was the Catalan furnace, so named from
the province of Catalonia, where it probably first originated, and it is
still so known and extensively used. “It consists of a four-sided cavity
or hearth, which is always placed within a building and separated from
the main wall thereof by a thinner interior wall, which in part
constitutes one side of the furnace. The blast pipe comes through the
wall, and enters the fire through a flue which slants downward. The
bottom is formed of a refractory stone, which is renewable. The furnace
has no chimneys. The blast is produced by means of a fall of water
usually from 22 to 27 feet high, through a rectangular tube, into a
rectangular cistern below, to whose upper part the blast pipe is
connected, the water escaping through a pipe below. This apparatus is
exterior to the building, and is said to afford a continuous blast of
great regularity; the air, when it passes into the furnace, is, however,
saturated with moisture.”--_Knight._
No doubt in such a heat was formed the metal from which was shaped the
armour of Don Quixote and his prototypes.
Bell in his history of Metallurgy tells us that the manufacture of
malleable iron must have fallen into decadence in England, especially
before the reign of Elizabeth and Charles I., as no furnaces equal even
to the Catalan had for a long time been in use; and the architectural
iron column found in ancient Delhi, 16 inches in diameter, about 48 feet
long and calculated to weigh about 17 tons, could not have been formed
by any means known in England in the sixteenth century. This decadence
was in part due to the severe laws enacted against the destruction of
forests, and most of the iron was then brought to England from Germany
and other countries.
From time immemorial the manufacture of iron and steel has been followed
in Germany, and that country yet retains pre-eminence in this art both
as to mechanical and chemical processes. It was in the eighteenth
century that the celebrated Freiberg Mining Academy was founded, the
oldest of all existing mining schools; and based on developing mining
and metallurgy on scientific lines, it has stood always on the battle
line in the fight of progress.
The early smelting furnaces of Germany resembled the Catalan, and were
called the “Stückofen,” and in Sweden were known as the “Osmund.” In
these very pure iron was made.
The art of making cast iron, which differs from the ordinary smelted
iron in the fact that it is _melted_ and then run into moulds, although
known among the ancients more than forty centuries ago, as shown by the
castings of bronze and brass described by their writers and recovered
from their ruins, appears to have been forgotten long before the
darkness of the middle ages gathered. There is no record of its practice
from the time the elder Pliny described its former use (40-79 A. D.), to
the sixteenth century. It is stated that then the lost art was
re-invented by Ralph Page and Peter Baude of England in 1543--who in
that year made cast-iron in Sussex.
The “Stückofen” furnace above referred to was succeeded in Germany by
higher ones called the “Flossofen,” and these were followed by still
higher and larger ones called “Blauofen,” so that by the middle of the
eighteenth century the furnaces were very capacious, the blast was good,
and it had been learned how to supply the furnaces with ore, coal and
lime-stone broken into small fragments. The lime was added as a flux,
and acted to unite with itself the sand, clay and other impurities to
form a slag or scoria. The melted purified iron falling to the bottom
was drawn off through a hole tapped in the furnace, and the molten metal
ran into channels in a bed of sand called the “Sow and pigs.” Hence the
name, “pig iron.”
The smelting of ore by charcoal in those places where carried on
extensively required the use of a vast amount of wood, and denuded the
surrounding lands of forests. So great was this loss felt that it gave
rise to the prohibitory laws and the decadence in England of the
manufacture of iron, already alluded to. This turned the attention of
iron smelters to coal as a substitute. Patents were granted in England
for its use to several unsuccessful inventors. Finally in 1619 Dud
Dudley, a graduate of Oxford University, and to whom succeeded his
father’s iron furnaces in Worcestershire, obtained a patent and
succeeded in producing several tons of iron per week by the use of the
pitcoal in a small blast furnace.
This success inflamed the wood owners and the charcoal burners and they
destroyed Dudley’s works. He met with other disasters common to worthy
inventors and discontinued his efforts to improve the art.
It is said that in 1664 Sir John Winter of England made coke by burning
sea coal in closed pots. But this was not followed up, and the use of
charcoal and the destruction of the forests went on until 1735, when
Abraham Darby of the Coalbrookdale Iron Works at Shropshire, England,
commenced to treat the soft pit coal in the same way as wood is treated
in producing charcoal. He proposed to burn the coal in a smouldering
fire, to expel the sulphur and other impurities existing in the form of
phosphorus, hydrogen and oxygen, etc. while saving the carbon. The
attempt was successful, and thus _coke_ was made. It was found cheaper
and superior to either coal or charcoal, and produced a quicker fire and
a greater heat. This was a wonderful discovery, and was preserved as a
trade secret for a long time. It was referred to as a curiosity in the
_Philosophical Transactions_ in 1747. In fact it was not introduced in
America until a century later, when in 1841 the soft coal abounding
around Pittsburgh in Pennsylvania and in the neighbouring regions of
Ohio was thus treated. Even its use then was experimental, and did not
become a practical art in the United States until about 1860.
With the invention of coke came also the revival of cast iron.
The process of making cast steel was reinvented in England by Benjamin
Huntsman of Attercliff, near Sheffield, about 1740. Between that time
and 1770 he practised melting small pieces of “blistered” steel (iron
bars which had been carbonised by smelting in charcoal) in closed clay
crucibles.
In 1784 Henry Cort of England introduced the puddling process and
grooved rolls. Puddling had been invented, but not successfully used
before. The term “puddling” originated in the covering of the hearth of
stones at the bottom of the furnace with clay, which was made plastic by
mixing the clay in a puddle of water; and on which hearth the ore when
melted is received. When in this melted condition Cort and others found
that the metal was greatly improved by stirring it with a long iron bar
called a “rabble,” and which was introduced through an opening in the
furnace. This stirring admitted air to the mass and the oxygen consumed
and expelled the carbon, silicon, and other impurities. The process was
subsequently aided by the introduction of pig iron broken into pieces
and mixed with hammer-slag, cinder, and ore. The mass is stirred from
side to side of the furnace until it comes to a boiling point, when the
stirring is increased in quickness and violence until a pasty round mass
is collected by the puddler. As showing the value of Cort’s discovery
and the hard experience inventors sometimes have, Fairbairn states that
Cort “expended a fortune of upward of £20,000 in perfecting his
invention for puddling iron and rolling it into bars and plates; that he
was robbed of the fruits of his discoveries by the villainy of officials
in a high department of the government; and that he was ultimately left
to starve by the apathy and selfishness of an ungrateful country. His
inventions conferred an amount of wealth on the country equivalent to
£600,000,000, and have given employment to 600,000 of the working
population of our land for the last three or four generations.” This
process of puddling lasted for about an hour and a half and entailed
extremely severe labour on the workman.
The invention of mechanical puddlers, hereinafter referred to,
consisting chiefly of rotating furnaces, were among the beneficent
developments of the nineteenth century.
Prior to Cort’s time the plastic lump or ball of metal taken from the
furnace was generally beaten by hammers, but Cort’s grooved rollers
pressed out the mass into sheets.
The improvements of the steam engine by Watt greatly extended the
manufacture of iron toward the close of the 18th century, as powerful
air blasts were obtained by the use of such engines in place of the
blowers worked by man, the horse, or the ox.
So far as the art of refining the precious metals is concerned, as well
as copper, tin and iron, it had not, previous to this century, proceeded
much beyond the methods described in the most ancient writings; and
these included the refining in furnaces, pots, and covered crucibles,
and alloying, or the mixture and fusion with other metals. Furnaces to
hold the crucibles, and made of iron cylinders lined with fire brick,
whereby the crucibles were subjected to greater heat, were also known.
The amalgamating process was also known to the ancients, and Vitruvius
(B. C. 27) and Pliny (A. D. 79), describe how mercury was used for
separating gold from its impurities. Its use at gold and silver mines
was renewed extensively in the sixteenth century.
Thus we find that the eighteenth century closed with the knowledge of
the smelting furnaces of various kinds, of coke as a fuel in place of
charcoal, of furious air blasts driven by steam and other power, of cast
iron and cast steel, and of refining, amalgamating, and compounding
processes.
Looking back, now, from the threshold of the nineteenth century over the
path we have thus traced, it will be seen that what had been
accomplished in metallurgy was the result of the use of ready means
tested by prolonged trials, of experiments more or less lucky in fields
in which men were groping, of inventions without the knowledge of the
real properties of the materials with which inventors were working or of
the unvarying laws which govern their operations. They had accomplished
much, but it was the work mainly of empirics. The art preceding the
nineteenth century compared with what followed is the difference between
experience simply, and experience when combined with hard thinking,
which is thus stated by Herschel: “Art is the application of knowledge
to a practical end. If the knowledge be merely accumulated experience
the art is empirical; but if it is experience reasoned upon and brought
under general principles it assumes a higher character and becomes a
scientific art.”
With the developments, discoveries and inventions in the lines of steam,
chemistry and electricity, as elsewhere told, the impetus they gave to
the exercise of brain force in every field of nature at the outset of
the century, and with their practical aid, the art of metallurgy soon
began to expand to greater usefulness, and finally to its present
wonderful domain.
The subject of metallurgy in this century soon became scientifically
treated and its operations classified.
Thus the physical character and metallic constituents of ores received
the first consideration; then the proper treatment to which the ores
were to be subjected for the purpose of extracting the metal--which are
either mechanical or chemical. The mechanical processes designed to
separate the ore from its enclosing rock or other superfluous earthy
matter called _gangue_ became known as _ore dressing_ and _ore
concentrating_. These included mills with rollers, and stamps operated
by gravity, or steam, for breaking up the ore rocks; abrasion apparatus
for comminuting the ore by rubbing the pieces of ore under pressure; and
smelting, or an equivalent process, for melting the ore and driving off
the impurities by heat, etc. The chemical processes are those by which
the metal, whatever it may be, is either dissolved or separated from
other constituents by either the application to the ore of certain
metallic solutions of certain acids, or by the fusion of different ores
or metals in substantially the old styles of furnaces; or its
precipitation by amalgamating, or by electrolysis--the art of
decomposing metals by electricity.
In the early decades of the century, by the help of chemistry and
physics, the nature of heat, carbon, and oxygen, and the great affinity
iron has for oxygen, became better known; and particularly how in the
making of iron its behaviour is influenced by the presence of carbon and
other foreign constituents; also how necessary to its perfect separation
was the proper elimination of the oxygen and carbon. The use of
manganese and other highly oxidisable metals for this purpose was
discovered.
Among the earliest most notable inventions in the century, in the
manufacture of iron, was that of Samuel B. Rogers of Glamorganshire,
Wales, who invented the iron floor for furnaces with a refractory
lining--a great improvement on Cort’s sand floor, which gave too much
silicon to the iron; and the _hot air blast_ by Neilson of Glasgow,
Scotland, patented in 1828. The latter consisted in the use of heated
air as the blast instead of cold air--whereby ignition of the fuel was
quickened, intensity of the heat and the expulsion of oxygen and carbon
from the iron increased, and the operation shortened and improved in
every way. The patent was infringed and assailed, but finally sustained
by the highest courts of England. It produced an immense forward stride
in the amount and quality of iron manufactured.
By the introduction of the hot air blast it became practicable to use
the hard anthracite coal as a fuel where such coal abounded; and to use
pig iron, scrap iron, and refractory ore and metals with the fuel to
produce particular results. Furnaces were enlarged to colossal
dimensions, some being a hundred feet high and capable of yielding 80 or
100 tons of metal per day.
The forms of furnaces and means for lining and cooling the hearth and
adjacent parts have received great attention.
The discovery that the flame escaping from the throat of the blast
furnace was nothing else than burning carbon led Faber du Faur at
Wasseralfugen in 1837 to invent the successful and highly valuable
method of utilising the unburnt gas from the blast furnace for heating
purposes, and to heat the blast itself, and drive the steam engine that
blew the blast into the furnace, without the consumption of additional
fuel. This also led to the invention of separate gas producers. Bunsen
in 1838 made his first experiments at Hesse in collecting the gases from
various parts of the furnace, revealing their composition and showing
their adaptability for various purposes. Thus, from a scientific
knowledge of the constituents of ores and of furnace gases, calculations
could be made in advance as to the materials required to make pig iron,
cast iron, and steel of particular qualities.
In the process of puddling difficulty had been experienced in handling
the bloom or ball after it was formed in the furnace. A sort of
squeezing apparatus, or tongs, called the alligator, had been employed.
In 1840 Henry Burden of America invented and patented a method and means
for treating these balls, whereby the same were taken directly from the
furnace and passed between two plain converging metal surfaces, by which
the balls were gradually but quickly pressed and squeezed into a
cylindrical form, while a large portion of the cinders and other foreign
impurities were pressed out.
We have described how by Cort’s puddling process tremendous labour was
imposed on the workmen in stirring the molten metal by hand with
“rabbles.” A number of mechanical puddlers were invented to take the
place of these hand means, but the most important invention in this
direction was the revolving puddlers of Beadlestone, patented in 1857 in
England, and of Heaton, Allen and Yates, in 1867-68. The most
successful, however, was that of Danks of the United States in 1868-69.
The Danks rotary puddler is a barrel-shaped, refractory lined vessel,
having a chamber and fire grate and rotated by steam, into which pig
iron formed by the ordinary blast furnaces, and then pulverised, is
placed, with the fuel. Molten metal from the furnace is then run in,
which together with the fuel is then subjected to a strong blast.
Successive charges may be made, and at the proper time the puddler is
rotated, slowly at some stages and faster at others, until the operation
is completed. A much more thorough and satisfactory result in the
production of a pure malleable iron is thus obtained than is possible by
hand puddling.
But the greatest improvements in puddling, and in the production of
steel from iron, and which have produced greater commercial results than
any other inventions of the century relating to metallurgy, were the
inventions of Henry Bessemer of Hertfordshire, England, from 1855 to
1860. In place of the puddling “rabbles” to stir the molten metal, or
_matte_, as it is called, while the air blast enters to oxidise it, he
first introduced the molten metal from the furnace into an immense
egg-shaped vessel lined with quartzose, and hung in an inclined position
on trunnions, or melted the metal in such vessel, and then dividing the
air blast into streams forced with great pressure each separate stream
through an opening in the bottom of the vessel into the molten mass,
thus making each stream of driven air a rabble; and they together blew
and lifted the white mass into a huge, surging, sun-bright fountain. The
effect of this was to burn out the impurities, silicon, carbon, sulphur,
and phosphorus, leaving the mass a pure soft iron. If steel was wanted a
small amount of carbon, usually in the form of spiegeleisen, was
introduced into the converter before the process was complete.
A. L. Holley of the United States improved the Bessemer apparatus by
enabling a greater number of charges to be converted into steel within a
given time.
Sir Henry Bessemer has lived to gain great fortunes by his inventions,
to see them afford new fields of labour for armies of men, and to
increase the riches of nations, from whom he has received deserved
honours.
The Bessemer process led to renewed investigations and discoveries as to
heat and its utilisation, the constituents of different metals and their
decomposition, and as to the parts played by carbon, silicon, and
phosphorus. The carbon introduced by the charge of pig iron in the
Bessemer process was at first supposed to be necessary to produce the
greatest heat, but this was found to be a mistake; and phosphorus, which
had been regarded as a great enemy of iron, to be eliminated in every
way, was found to be a valuable constituent, and was retained or added
to make phosphorus steel.
The Bessemer process has been modified in various ways: by changing the
mode of introducing the blast from the bottom of the converter to the
sides thereof, and admitting the blast more slowly at certain stages; by
changing the character of the pig iron and fuel to be treated; and by
changing the shape and operation of the converters, making them
cylindrical and rotary, for instance.
The Bessemer process is now largely used in treating copper. By this
method the blowing through the molten metal of a blast of air largely
removes sulphur and other impurities.
The principles of reduction by the old style furnaces and methods we
have described have been revived and combined with improvements. For
instance, the old Catalan style of furnace has been retained to smelt
the iron, but in one method the iron is withdrawn before it is reduced
completely and introduced into another furnace, where, mixed with
further reducing ingredients, a better result by far is produced with
less labour.
It would be a long list that would name the modern discoverers and
inventors of the century in the manufacture of iron and steel. But
eminent in the list, in addition to Davy and Bessemer, and others
already mentioned, are Mushet, Sir L. Bell, Percy, Blomfield, Beasley,
Giers and Snellus of England; Martin, Chennot, Du Motay, Pernot and
Gruner of France; Lohage, Dr. C. L. Siemens and Höpfer of Germany; Prof
Sarnstrom and Akerman of Sweden; Turner of Austria; and Holley, Slade,
Blair, Jones, Sellers, Clapp, Griffiths and Eames of the United States.
Some of the new metals discovered in the last century have in this
century been combined with iron to make harder steel. Thus we have
nickel, chromium, and tungsten steel. Processes for hardening steel, as
the “Harveyized” steel, have given rise to a contest between
“irresistible” projectiles and “impenetrable” armour plate.
If there are some who regard modern discoveries and inventions in iron
and steel as lessening the number of workmen and cheapening the product
too much, thus causing trouble due to labour-saving machinery, let them
glance, among other great works in the world, at Krupp’s at Essen, where
on January 1st, 1899, 41,750 persons were employed, and at which works
during the previous year 1,199,610 tons of coal and coke were consumed,
or about 4000 tons daily. Workers in iron will not be out of employment
in the United States, where 16,000,000 tons of coke are produced
annually, 196,405,953 tons of coal mined, 11,000,000 tons of pig iron
and about 9,000,000 tons of steel made. The increase of population
within the last hundred years bears no comparison with this enormous
increase in iron and fuel. It shows that as inventions multiply, so does
the demand for their better and cheaper products increase.
As the other metals, gold, silver, copper and lead often occur together,
and in the same deposits with iron, the same general modes of treatment
to extract them are often applied. These are known as the dry and the
wet methods, and electro-reduction.
Ever since Mammon bowed his head in search for gold, every means that
the mind of man could suggest to obtain it have been tried, but the
devices of this century have been more numerous and more successful than
any before. The ancient methods of simply melting and “skimming the
bullion dross” have been superseded. Modern methods may be divided into
two general classes, the mechanical and the chemical. Of the former
methods, when gold was found loose in sand or gravel, washing was the
earliest and most universally practised, and was called panning. In this
method mercury is often used to take up and secure the fine gold.
Rockers like a child’s cradle, into which the dirt is shovelled and
washed over retaining riffles, were used; coarse-haired blankets and
hides; sluices and separators, with or without quicksilver linings to
catch the gold; and powerful streams of water worked by compressed air
to tear down the banks. Where water could not be obtained the ore and
soil were pulverised and dried, and then thrown against the wind or a
blast of air, and the heavier gold, falling before the lighter dust, was
caught on hides or blankets. For the crushing of the quartz in which
gold was found, innumerable inventions in stamp mills, rollers,
crushers, abraders, pulverisers and amalgamators have been invented; and
so with roasters, and furnaces, and crucibles to melt the precious
metal, separate the remaining impurities and convert it to use.
As to chemical methods for the precious metals, the process of
_lixiviation_, or _leaching_, by which the ore is washed out by a
solution of potash, or with dilute sulphuric acid, or boiling with
concentrated sulphuric acid, is quite modern. About 1889 came out the
great cyanide process, also known as the MacArthur-Forrest process (they
being the first to obtain patents and introduce the invention),
consisting of the use of cyanide potassium in solution, which dissolves
the gold, and which is then precipitated by the employment of zinc. This
process is best adapted to what are known as free milling or porous
ores, where the gold is free and very fine and is attracted readily by
mercury.
In 1807, Sir Humphry Davy discovered the metal potassium by subjecting
moistened potash to the action of a powerful voltaic battery; the
positive pole gave off oxygen and the metallic globules of pure
potassium appeared at the negative pole. It is never found uncombined in
nature. Now if potassium is heated in cyanogen gas (a gas procured by
heating mercury) or obtained on a large scale by the decomposition of
yellow prussiate of potash, a white crystalline body very soluble in
water, and exceedingly poisonous, is obtained. When gold, for instance,
obtained by pulverising the ore, or found free in sand, is treated to
such a solution it is dissolved from its surrounding constituents and
precipitated by the zinc, as before stated.
Chlorine is another metal discovered by Scheele in 1774, but not known
as an elementary element until so established by Davy’s investigations
in 1810, when he gave it the name it now bears, from the Greek
_chloras_, yellowish green. It is found abundantly in the mineral world
in combination with common salt. Now it was found that chlorine is one
of the most energetic of bodies, surpassing even oxygen under some
circumstances, and that a chlorine solution will readily dissolve gold.
These, the cyanide and chlorination processes, have almost entirely
superseded the old washing and amalgamating methods of treating free
gold--and the cyanide seems to be now taking the lead.
_Alloys._--The art of fusing different metals to make new compounds,
although always practised, has been greatly advanced by the discoverers
and inventors of the century. As we have seen, amalgamating to extract
gold and silver, and the making of bronze from tin and copper were very
early followed. One of the most notable and useful of modern inventions
or improvements of the kind was that of Isaac Babbitt of Boston in 1839,
who in that year obtained patents for what ever since has been known as
“babbitting.” The great and undesirable friction produced by the rubbing
of the ends of journals and shafts in their bearings of the same metal,
cast or wrought iron, amounting to one-fifth of the amount of power
exerted to turn them, had long been experienced. Lubricants of all kinds
had been and are used; but Babbitt’s invention was an anti-friction
metal. It is composed of tin, antimony, and copper, and although the
proportions and ingredients have since been varied, the whole art is
still known as babbitting.
Other successful alloys have been made for gun metal, sheathing of
ships, horseshoes, organ pipes, plough shares, roofing, eyelets,
projectiles, faucets, and many and various articles of hardware,
ornamental ware, and jewelry.
Valuable metals, such as were not always rare or scarce, but very hard
to reduce, have been rendered far less in cost of production and more
extensive in use by modern processes. Thus, aluminium, an abundant
element in rocks and clay, discovered by the German chemist Wöhler, in
1827, a precious metal, so light, bright, and tough, non-oxidizing,
harder than zinc, more sonorous than silver, malleable and ductile as
iron, and more tenacious, has been brought to the front from an
expensive and mere laboratory production to common and useful purposes
in all the arts by the processes commencing in 1854 with that of St.
Clair Deoville, of France, followed by those of H. Rose, Morin, Castner,
Tissier, Hall, and others.
_Electro-metallurgy_, so far, has chiefly to do with the decomposition
of metals by the electric current, and the production of very high
temperatures for furnaces, by which the most refractory ores, metals,
and other substances may be melted, and results produced not obtainable
in any other way. By placing certain mixtures of carbon and sand, or of
carbon and clay, between the terminals of a powerful current, a material
resembling diamonds, but harder, has been produced. It has been named
carbonundrum. The production of diamonds themselves is looked for. Steel
wire is now tempered and annealed by electricity, as well as welding
done, of which mention further on will be made.
Thus we have seen how the birth of ideas of former generations has given
rise in the present age to children of a larger growth. Arts have grown
only as machinery for the accomplishment of their objects has developed,
and machinery has waited on the development of the metals composing it.
The civilisation of to-day would not have been possible if the
successors of Tubal Cain had not been like him, instructors “of every
artificer in brass and iron.”