be extracted from the hard mass? how can a stone of a few grains weight
be found amongst 1,600 lbs. of miscellaneous matter—a thing perhaps not
larger than a peppercorn in four cubic feet of compact material? The
“blue ground” is spread out on levelled and carefully prepared areas
called “depositing floors,” and there, after a few months’ exposure, all
but the very hardest pieces crumble down, the atmospheric action being
accelerated by turning the material over with harrows, and by occasional
waterings. The “blue ground” from the De Beers mine requires at least
six months of this treatment, and it contains a certain proportion of
refractory lumps that would not disintegrate in perhaps less than two
years. These lumps are coarsely crushed between rollers, and the
fragments are spread over slowly moving tables, from which any larger
diamonds are picked off; the fragments left go through smaller crushers,
and are subjected to still greater concentration. The depositing floors
of the De Beers mine are laid out as rectangles, 600 yards long by 200
yards wide, each holding about 50,000 loads. They occupy several square
miles, and as the “blue ground” spread upon them is always one of the
most valuable assets of the company, the quantity of it forms an
important item in the balance-sheets, and the amount that can be
realized from it can be estimated with sufficient closeness, on account
of the nearly uniform distribution of the diamonds. Thus in June 1895,
the 3,360,256 loads then on the floors were put down as equivalent to
nearly 1 million pounds sterling. When the “ground,” thoroughly
weathered, has become yellow and friable, it is transferred to the
washing machinery, by which about 99 per cent, of the original
non-diamondiferous material is removed, and, thus concentrated, the
gravel is together with the mechanically crushed material submitted to
the action of a machine called the _pulsator_, where the gravel is first
assorted into sizes by being turned about within an inclined iron
cylinder perforated with several stages of round holes of diameters
successively of 2, 3, 4 and 6 sixteenths of an inch. The pieces that are
too coarse to pass through the largest holes are taken to the _sorting
house_ direct; but the stones that have passed through the cylinder drop
according to their sizes into four separate sieves called at Kimberley
_jigs_, from the well-known mining term _jigger_, applied to a man who
washes ores in a sieve. The several jigs into which passes the now
assorted gravel have screens with meshes corresponding to the holes in
the cylinder; and by a very ingenious arrangement the concentration is
carried to the point at which the diamonds can be individually picked
out. The “jigs” themselves do not move, but all over the meshes of the
screen is spread a layer of leaden bullets, which prevent a too rapid
passage through the screens, while the material is kept moving in water,
by that liquid _pulsating_ or emerging in quickly succeeding gushes from
below the meshes, and thus carrying off the lighter matters, while those
of greater specific gravity, including the diamonds, work their way
downwards between the bullets and through the meshes, and are received
in boxes which are periodically carried to the sorting house.
When the now much concentrated diamondiferous gravel reaches the sorting
house, the remaining operation consists merely in picking the diamonds
out. But simple as this operation is, it has to be conducted
systematically. In the sorting house are long tables covered with plates
of iron, and placed in a good light. Upon these is thrown the wet
gravel, but not promiscuously; the different sizes being set apart, the
sorter spreads out the heap before him with a flat piece of zinc, picks
out the diamonds and drops them into a small box. Only white men in whom
confidence can be placed are allowed to deal with largest sized
material, for this offers the strongest temptation to purloiners, as in
this of course the most valuable stones are met with. This material,
after the first search, is submitted to the scrutiny of another person,
to see that no diamond has been overlooked; but the smaller assortments
are examined by blacks, who are closely supervised by white men. The
value of the diamonds occasionally sorted out in a single day may reach
£10,000.
At the diamond mines little trust is reposed in the honesty of the
blacks. Below ground and above ground they work under the constant
surveillance of white men, and they live in “compounds” which are
spacious areas—perhaps of 20 acres in extent—enclosed by lofty iron
fences, and containing long rows of corrugated iron erections divided
into rooms, each appropriated to a score of natives. Food, etc., is
supplied from a store at less than ordinary prices, and the company find
fuel and water gratis, and provide a well equipped hospital and medical
attendance. There are swimming baths, and ample recreation grounds for
dancing, etc. The natives of each of the many tribes keep by themselves
apart, and follow their own fancies. They receive good wages, and some
of them save money. They are not allowed out of the “compound” or the
mine, except to work on the depositing floor, which they do under guard.
They accept their restrictions voluntarily, making agreements for a
certain term, three months being the least. Those who leave, as many do
to spend their earnings, often “not wisely but too well,” usually
return. The depositing floors are surrounded by fences 7 feet high,
unscalably and impenetrably armed with barbed wire; and as here robbery
would have the readiest chance, where the largest stones might be met
with, extraordinary precautions are taken, watch and ward being
maintained by day and by night. Not more vigilantly did Cerberus keep
the entrance of Pluto’s domain, nor the wakeful dragon guard the golden
apples of the Hesperides, than the patrols observe the depositing
floors. At night powerful electric searchlights are made to play across
the enclosures, so that unauthorized movements can scarcely escape
detection. Besides these provisions against theft, the laws of the
Colony prohibit any attempt at illicit dealing in diamonds, under a
penalty of two years’ penal servitude.
The maximum penalties for contravention of the Diamond Laws are,
however, much more severe, and that to an extraordinary degree. Thus any
unlicensed dealer is liable to a fine of £1,000, or fifteen years’
imprisonment, or both. And the authorized dealers are required to keep a
most minute record of all their transactions, to send a copy of it every
month to the head of the police, and to produce it when required. It is
needless to say that extraordinary precautions are taken to prevent the
native workmen from secreting diamonds. And any person even finding a
diamond, and neglecting to report the circumstance to the proper quarter
at once, is liable to the pains and penalties above mentioned.
The “blue ground” was at first supposed to be the original home of the
diamond, within which it had somehow taken its shape. But no
satisfactory explanation was forthcoming as to the state of the carbon
before its solidification into the crystalline form. The more general
opinion has been in favour of a volcanic origin due to very high
temperature; and although the “blue ground” itself is clearly not the
ordinary erupted matter of volcanoes due to igneous fusion, the geology
points to the district having been the scene of very active and
extensive volcanic energies at more than one remote period, for the bed
of the Karoo inland sea has been several times covered by level sheets
of molten matter extruded somewhere from below; but not through the
“pipes,” which were blown out ages afterwards. The strata of basalt and
of hornblendic mineral, which extend horizontally over great areas in
the Karoo formation, are of igneous origin, as are also some nearly
vertical dykes of trap rock, about 7 feet wide, that are found
traversing the “blue ground” in certain directions. These intrusive
dykes are of course more recent than the formation of the blue ground,
and that is itself later than the production of the pipes. The fact of
many fragments of crystals being found in the “blue ground” does not
comport with the theory that supposes it to be the matrix; and besides
this, many of the diamonds show scratches, and as these are producible
only by other diamonds, it would appear that they must all have
travelled in company, some part of their journey at least.
Carbon in any form is quite infusible at the highest temperature we have
hitherto been able to produce, although an incipient softening under the
influence of the electric arc has been suspected. Professor Dewar, an
English chemist, basing his data on analogies with other substances, and
on purely theoretical grounds, has calculated that the melting
temperature of carbon is near 3,600° C. (6,512° F.), and that it cannot
remain in a liquid state at a temperature exceeding 5,527° C., when its
vapour would have a tension equivalent to a pressure of 15 tons on the
square inch. So far as these deductions are correct, both the melting
point of carbon and the boiling point of its liquid must lie within the
range of temperature expressed by 3,600° C. and 5,527° C. The most
intense heat we can produce is that developed in the electric arc
discharge, and an eminent French chemist and metallurgist, M. Moissan,
by employing special arrangements and very powerful currents, has thus
been able to obtain in his “electric furnace” a temperature estimated at
3,500° C., which nearly approaches the lower of the above-mentioned
limits, and he has thereby produced many new and unexpected chemical
combinations of refractory elements. Among the most striking of his
results is the formation artificially of real crystalline diamonds. He
found that carbon is freely dissolved by several of the metals in fusion
at the temperature of the electric furnace. When the carbon separated
from the metals, as they cooled and became solid, it was always in the
condition of graphite. The carbons of the electric poles were readily
attacked by molten iron, and it was from the solution of carbon in iron
that Moissan prepared his diamonds. The fact of carbon thus combining
with iron was of course no discovery, as the reader already knows; and
the resulting combination was found, on allowing the metal to cool, to
be simply cast iron, the greater part of the carbon separating out in
the graphitic form. But M. Moissan, having studied the conditions of the
Kimberley mines, and recognizing the probability of the diamonds having
taken their origin at very great depths, where the pressure due to the
weight of superincumbent strata would be immense, was struck with the
idea of _pressure_ being in some way a factor in their formation; and it
occurred to him that the carbon might separate from its liquid condition
in the iron in the crystalline, and not in the graphitic form, if the
solidification could be effected under great pressure. The apparently
insurmountable difficulty of applying an enormous pressure to a small
quantity of molten iron (half a pound) yielded to the experimenter’s
ingenuity. He took advantage of the circumstance that cast iron at the
moment of solidification expands, a property upon which depends its use
for many purposes. If then the fused mass were suddenly cooled on the
outside, we should have a shell of solid iron enclosing a nucleus of
still fluid metal, which, on cooling in its turn, would tend to expand,
and by so doing would exert a great pressure within the shell by which
it was confined. At first Moissan plunged his glowing crucible into cold
water, but a method of more rapidly cooling it was to immerse it in
melted lead. It seems a strange proceeding to cool the crucible by
surrounding it with hot metal, yet the _difference_ of the temperatures
was sufficient to produce the desired effect, the cooling contact of
water not really operating on the intensely heated body, which becomes
separated from the liquid by a coating of _steam_. When the mass of iron
was dissolved off, diamonds of all kinds were found in the residue, and,
though extremely small, some crystals were perfect in shape and colour;
every variety that occurred in the mines being found reproduced in tiny
size. There was also some graphite in the residue. Many more crystals of
“pure water” were obtained by the lead-cooling than by the
water-cooling, as the former process gave some flawless cubes and
octahedra. The largest of the set was only 1/50 inch across, and
although of perfect form when first extracted, within the course of
three months it had spontaneously split up into fragments.
There was evidently no danger of M. Moissan’s manufacture of diamonds
from coke causing consternation at Kimberley; though it would not be
without interest to speculate upon the consequences had the French
_savant_ achieved the greater triumph of turning out carbon crystals in
every respect equal to the productions of nature’s own laboratories.
What a drop there would have been in the shares of the De Beers Mines
Consolidated! What heaviness of heart would have fallen upon those great
ladies who exult in the exclusive possession of priceless tiaras and
precious necklaces flashing with the resplendent gems! From a scientific
point of view, M. Moissan’s fabrication of even those minute crystals,
which so soon spontaneously crumbled into fragments, is a distinct and
valuable success; for, notwithstanding their diminutive size and
instability, they show us that art has so far succeeded in imitating the
processes of nature, that some of her secrets have been revealed. Though
we know the exact chemical composition of all kinds of crystallized
minerals, very very few of these have we been able to imitate
artificially. Nor is this to be wondered at; for nature’s resources are
immense compared with ours: she can command temperatures unlimited by
which to form her solutions or liquefactions; prodigious pressures to
keep them close; and time immeasurable—geological time—in which to let
them cool, and their particles freely coalesce into geometric forms.
Human agency, being obviously unable to reproduce, even on the smallest
scale, such conditions as attended the deposition and slow cooling of
the earth’s crust, may not hope to rival the products of the planet’s
prime. So the fair owners of the earth-born gems may possess their souls
in peace, free from any fear of the chemists’ crucibles; and the
Kimberley Diamond Companies are not likely to suffer panics from the
results of scientific researches, and probably will continue to pay
their handsome dividends for time indefinite.
But curiously enough, a discovery of the latest years of our century has
revealed the existence of diamonds in a region not mapped by the most
advanced of geographers—a region which indeed cannot be defined by
degrees of latitude and longitude. In the recesses of an unquestionable
meteorite—one of those celestial lumps of iron of which mention has been
made in the earlier pages of this volume—real diamonds have been found.
These quite resembled the products of M. Moissan’s experiments, being
extremely small, but including clear and perfectly shaped crystals,
associated with black ones, and also with much graphite in more or less
definite forms. So very limited, however, could be the quantity of
diamonds obtainable from this hitherto unsuspected source, that even if
they rivalled in quality the finest stones from the South African mines,
it might be difficult to form a “Company” for their _exploitation_.
Still, there is the possibility of some one falling in with a little
meteorite containing some mature full-sized carbon crystals, and such a
one might be considered equally fortunate with the finder of the famous
Australian nugget “Welcome” (£25,000). The association of diamonds with
the ferruginous matter of the “blue ground” in the Kimberley pipes,
their crystallization out of iron in M. Moissan’s experiments, and their
presence in iron meteorites, would seem to point to special relations
between the two elements, iron and carbon. Some of these relations are
exemplified in another way by the profound modification effected in the
physical properties of iron, by its combination with a very small
quantity of carbon, as in some kinds of steel; or again, by the
differences between white cast iron and grey cast iron, as determined by
the condition of the carbon in each.
[Illustration:
FIG. 335.—_Portrait of Sir Humphrey Davy._
]
NEW METALS.
The chemistry of the nineteenth century can boast of a series of
discoveries more brilliant and more numerous than ever belonged to any
other science within a like period. And the advantage to the world must
have been great, for chemistry more directly than any other branch of
knowledge ministers to the useful arts and promotes the comfort and
well-being of society. The science itself, as it now exists, is almost
the creation of the present age. But its recent developments cannot be
here discussed; nor, of the immense number of new products with which it
has enriched the world, can more than a very few be brought under the
reader’s notice in the remaining pages of the present work. Among the
most striking of the remarkable series of discoveries by which Sir
Humphrey Davy penetrated the mysteries of matter was the isolation of
the alkali metals—a circumstance which marks an important era in the
history of chemistry. That the alkalies were oxides of unknown metals
had indeed been previously surmised by chemists, from the fact of their
behaving like metallic oxides in neutralizing and combining with acids
to form the class of compounds called _salts_. All attempts to decompose
these alkalies had proved fruitless until Davy separated the metal
_potassium_ from potash, in 1807. When, however, this alkali had once
been proved a compound, more correct ideas were introduced into chemical
science; the nature of other alkalies and earths was explained in like
manner, and new and powerful re-agents were placed in the hands of the
chemist.
Davy first obtained potassium by exposing to the action of the voltaic
current a fragment of potash which had become moist on the surface by
exposure to the air. The battery was formed of the then unprecedented
combination of two hundred pairs of 6–inch plates on Wollaston’s plan,
which was constructed for the Royal Institution of London. The heat
produced by the passage of the current fused the potash, and globules of
metallic potassium were separated at the negative wire. This method
yielded the metal in very small quantities only, and at a great cost.
Gay Lussac and Thenard soon afterwards found that potassium could be
obtained more cheaply and in greater abundance when fused potash was
made to flow over iron-turnings heated to whiteness in a gun-barrel, and
the hydrogen and potassium vapour were passed into a cooled receiver, in
which the latter body was condensed. The metal is now obtained by
heating potassium carbonate with charcoal. For this purpose it suffices
to heat crude tartar in a covered vessel from which air is excluded. The
tartar is first calcined in a crucible until all combustible vapour has
been driven off. The charred mass, which now consists of potassium
carbonate mixed with finely-divided carbon, is then broken into lumps
and quickly introduced into a wrought-iron retort, which is heated in a
furnace to nearly a white heat. A receiver in the form of a flat iron
box, 12 in. long, 5 in. wide, and ¼ in. deep, is adapted to the neck of
the retort, and is kept cooled by the application of a wet cloth on the
outside. The potassium thus obtained is not pure, and it must be
distilled in an iron retort, as otherwise a powerfully detonating
compound is apt to be formed by a portion of the metal combining with
carbonic oxide.
Immediately after his discovery of potassium Davy obtained sodium in the
same manner, and Gay Lussac and Thenard also procured it by the same
process they used for the sister metal. Sodium is now extracted on the
manufacturing scale for use as an agent in the reduction of two other
metals, of which we shall have to speak. A mixture of dried sodium
carbonate, powdered charcoal, and chalk is heated in wrought-iron
cylinders, about 4 ft. long, 5 in. internal diameter, and ½ in. thick.
The chalk takes no part in the chemical action, but is added in order to
give the sodium carbonate when it fuses a pasty consistence, and thus
prevent the separation of the charcoal. A number of these iron cylinders
are set in a reverberatory furnace; but they are coated with fire-clay
and enclosed in earthenware tubes, to prevent their destruction by the
intense heat. To one end of each cylinder a receiver is adapted, of the
form and dimensions already described for potassium. The other extremity
is closed by an iron plug, luted with fire-clay. When the charge in a
cylinder is exhausted, a fresh one is introduced by removing the plug,
taking out the residue, and inserting a new supply of the mixture made
up in a canvas bag. The operation is therefore continuous, and the metal
obtained is nearly pure, as sodium does not exhibit the same tendency as
potassium to form compounds with carbonic oxide.
Potassium and sodium are extremely soft metals; they are lighter than
water, upon which they float, at the same time rapidly decomposing that
compound by displacing half the hydrogen, which is set on fire by the
heat. The instant a piece of potassium touches the surface of water, a
violet flame bursts forth; but with sodium no flame appears unless the
metal is dropped on warm water, or prevented from swimming about. Since
these metals are thus capable of displacing hydrogen from its
combination with oxygen at ordinary temperatures, it follows that they
must have a powerful affinity for oxygen; and, indeed, they can only be
preserved in rock oil, for they rapidly combine with the oxygen of the
air. The great attraction of these metals for oxygen, and for chlorine
and other similar bodies, induces the chemist to employ them for
separating such bodies from their combination with other metals. Sodium
is generally employed for this purpose, as being far cheaper than
potassium.
Among the sixty-nine elementary or undecomposable substances which,
variously combined, constitute the whole material of our planet, so far
as we are acquainted with it, no fewer than fifty-six are metals. Of
these fifty-six metals very few are found in a free or uncombined state,
like the gold described in the last article. On the contrary, the whole
of the metallic elements of the globe, with insignificant exceptions,
exist in nature in a state of combination with one or more of the other
thirteen non-metallic substances. In this condition they form the stony
masses which are termed the ores of the more common metals, and they
constitute also the earths, the metallic bases of which were, until
recent times, unsuspected and unknown. Davy followed up his discovery of
the metals of potash and soda by experimental demonstrations that the
earths _alumina_, _magnesia_, and others, were really oxides of metals;
and when the nature of these substances had once been established,
chemists soon devised means for readily obtaining their metallic bases
in an isolated form. The new metals which have been thus isolated all
deserve the attention of the chemist; and the general reader will
probably also regard with interest the processes by which two of these
new metals, for which practical applications have been found, are
extracted, and the properties which have caused them to be produced on
the commercial scale. These are _aluminium_, the metallic base of common
clay; and _magnesium_, the metallic base of common magnesia, and Epsom
salts, and a constituent of dolomite, or magnesian limestone.