A New Formation of Diamond
I have long speculated as to the possibility of obtaining artificially such pressures and temperatures as would fulfil the above conditions. In their researches on the gases from fired gunpowder and cordite, Sir Frederick Abel and Sir Andrew Noble obtained in closed steel cylinders pressures as great as 95 tons to the square inch, and temperatures as high as 4000° C. According to a paper recently communicated to the Royal Society, Sir Andrew Noble, exploding cordite in closed vessels, has obtained a pressure of 8000 atmospheres, or 50 tons per square inch, with a temperature reaching in all probability 5400° Ab.
Here, then, we have conditions favourable for the liquefaction of carbon, and were the time of explosion sufficient to allow the reactions to take place, we should certainly expect to get the liquid carbon to solidify in the crystalline state.[7]
By the kindness of Sir Andrew Noble I have been enabled to work upon some of the residues obtained in closed vessels after explosions, and I have submitted them to the same treatment that the granulated iron had gone through. After weeks of patient toil I removed the amorphous carbon, the graphite, the silica,[8] and other constituents of the ash of cordite, and obtained a residue among which, under the microscope, crystalline particles could be distinguished. Some of these particles, from their crystalline appearance and double refraction, were silicon carbide; others were probably diamonds. The whole residue was dried and fused at a good red heat in an excess of potassium bifluoride, to which was added, during fusion, 5 per cent of nitre. (Previous experiments had shown me that this mixture readily attacked and dissolved silicon carbide; unfortunately it also attacks diamond to a slight degree.) All the operations of washing and acid treatment were performed in a large platinum crucible by decantation (except the preliminary attack with nitric acid and potassium chlorate, when a hard glass vessel was used); the final result was washed into a shallow watch-glass and the selection made under the microscope. The residue, after thorough washing and then heating in fuming sulphuric acid, was washed, and the largest crystalline particles picked out and mounted.
From the treatment the residual crystals had undergone, chemists will agree with me that diamonds only could stand such an ordeal; on submitting them to skilled crystallographic authorities my opinion is confirmed. Speaking of the largest crystal, one eminent authority calls it “a diamond showing octahedral planes with dark boundaries due to high refracting index.” After careful examination, another authority writes of the same crystal diamond, “I think one may safely say that the position and angles of its faces, and of its cleavages, the absence of birefringence, and the high refractive index are all compatible with the properties of the diamond crystallising in the form of an octahedron. Others of the remaining crystals, which show a similar high refractive index, appeared to me to present the same features.”
It would have been more conclusive had I been able to get further evidence as to the density and hardness of the crystals; but from what I have already said I think there is no doubt that in these closed vessel explosions we have another method of producing the diamond artificially.
[CHAPTER X]
THE NATURAL FORMATION OF THE DIAMOND
An hypothesis is of little value if it only elucidates half a problem. Let us see how far we can follow out the ferric hypothesis to explain the volcanic pipes. In the first place we must remember these so-called volcanic vents are admittedly not filled with the eruptive rocks, scoriaceous fragments, etc., constituting the ordinary contents of volcanic ducts.
Certain artificial diamonds present the appearance of an elongated drop. I have seen diamonds which have exactly the appearance of drops of liquid separated in a pasty condition and crystallised on cooling. Diamonds are sometimes found with little appearance of crystallisation, but with rounded forms similar to those which a liquid might assume if kept in the midst of another liquid with which it would not mix. Other drops of liquid carbon retained for sufficient time above their melting-point would coalesce with adjacent drops, and on slow cooling would separate in the form of large perfect crystals. Two drops, joining after incipient crystallisation, might assume the not uncommon form of interpenetrating twin crystals.
Many circumstances point to the conclusion that the diamond of the chemist and the diamond of the mine are strangely akin as to origin. It is evident that the diamond has not been formed in situ in the blue ground. The genesis must have taken place at vast depths under enormous pressure. The explosion of large diamonds on coming to the surface shows extreme tension. More diamonds are found in fragments and splinters than in perfect crystals; and it is noteworthy that although these splinters and fragments must be derived from the breaking up of a large crystal, yet in only one instance have pieces been found which could be fitted together, and these occurred at different levels. Does not this fact point to the conclusion that the blue ground is not their true matrix? Nature does not make fragments of crystals. As the edges of the crystals are still sharp and unabraded, the locus of formation cannot have been very distant from the present sites. There were probably many sites of crystallisation differing in place and time, or we should not see such distinctive characters in the gems from different mines, nor indeed in the diamonds from different parts of the same mine.
I start with the reasonable supposition that at a sufficient depth[9] there were masses of molten iron at great pressure and high temperature, holding carbon in solution, ready to crystallise out on cooling. Far back in time the cooling from above caused cracks in superjacent strata through which water[10] found its way. On reaching the incandescent iron the water would be converted into gas, and this gas would rapidly disintegrate and erode the channels through which it passed, grooving a passage more and more vertical in the necessity to find the quickest vent to the surface. But steam in the presence of molten or even red-hot iron liberates large volumes of hydrogen gas, together with less quantities of hydrocarbons[11] of all kinds—liquid, gaseous, and solid. Erosion commenced by steam would be continued by the other gases; it would be easy for pipes, large as any found in South Africa, to be scored out in this manner.
Sir Andrew Noble has shown that when the screw stopper of his steel cylinders in which gunpowder explodes under pressure is not absolutely perfect, gas escapes with a rush so overpowering and a temperature so high as to score a wide channel in the metal. To illustrate my argument Sir Andrew Noble has been kind enough to try a special experiment. Through a cylinder of granite he drilled a hole 0·2 inch diameter, the size of a small vent. This was made the stopper of an explosion chamber, in which a quantity of cordite was fired, the gases escaping through the granite vent. The pressure was about 1500 atmospheres and the whole time of escape was less than half a second. The erosion produced by the escaping gases and by the heat of friction scored out a channel more than half an inch diameter and melted the granite along the course. If steel and granite are thus vulnerable at comparatively moderate gaseous pressure, it is easy to imagine the destructive upburst of hydrogen and water-gas, grooving for itself a channel in the diabase and quartzite, tearing fragments from resisting rocks, covering the country with debris, and finally, at the subsidence of the great rush, filling the self-made pipe with a water-borne magma in which rocks, minerals, iron oxide, shale, petroleum, and diamonds are violently churned in a veritable witch’s cauldron! As the heat abated the water vapour would gradually give place to hot water, which, forced through the magma, would change some of the mineral fragments into the existing forms of to-day.
Each outbreak would form a dome-shaped hill; the eroding agency of water and ice would plane these eminences until all traces of the original pipes were lost.
Actions such as I have described need not have taken place simultaneously. As there must have been many molten masses of iron with variable contents of carbon, different kinds of colouring matter, solidifying with varying degrees of rapidity, and coming in contact with water at intervals throughout long periods of geological time—so must there have been many outbursts and upheavals, giving rise to pipes containing diamonds. And these diamonds, by sparseness of distribution, crystalline character, difference of tint, purity of colour, varying hardness, brittleness, and state of tension, have the story of their origin impressed upon them, engraved by natural forces—a story which future generations of scientific men may be able to interpret with greater precision than is possible to-day.
[CHAPTER XI]
METEORIC DIAMONDS
Sensational as is the story of the diamond industry in South Africa, quite another aspect fixes the attention of the chemist. The diamonds come out of the mines, but how did they get in? How were they formed? What is their origin?
Gardner Williams, who knows more about diamonds than any man living, is little inclined to indulge in speculation. In his fascinating book he frankly says:
“I have been frequently asked, ‘What is your theory of the original crystallisation of the diamond?’ and the answer has always been, ‘I have none; for after seventeen years of thoughtful study, coupled with practical research, I find that it is easier to “drive a coach and four” through most theories that have been propounded than to suggest one which would be based on any non-assailable data.’ All that can be said is that in some unknown manner carbon, which existed deep down in the internal regions of the earth, was changed from its black and uninviting appearance to the most beautiful gem which ever saw the light of day.”
Another diamond theory appeals to the imagination. It is said the diamond is a gift from Heaven, conveyed to earth in meteoric showers. The suggestion, I believe, was first broached by A. Meydenbauer,[12] who says, “The diamond can only be of cosmic origin, having fallen as a meteorite at later periods of the earth’s formation. The available localities of the diamond contain the residues of not very compact meteoric masses which may, perhaps, have fallen in prehistoric ages, and which have penetrated more or less deeply, according to the more or less resistant character of the surface where they fell. Their remains are crumbling away on exposure to the air and sun, and the rain has long ago washed away all prominent masses. The enclosed diamonds have remained scattered in the river beds, while the fine light matrix has been swept away.”
According to this hypothesis, the so-called volcanic pipes are simply holes bored in the solid earth by the impact of monstrous meteors—the larger masses boring the holes, while the smaller masses, disintegrating in their fall, distributed diamonds broadcast. Bizarre as such a theory appears, I am bound to say there are many circumstances which show that the notion of the heavens raining diamonds is not impossible.
The most striking confirmation of the meteoric theory comes from Arizona. Here, on a broad open plain, over an area about five miles in diameter, have been scattered one or two thousand masses of metallic iron, the fragments varying in weight from half a ton to a fraction of an ounce. There is no doubt these masses formed part of a meteoric shower, although no record exists as to when the fall took place. Curiously enough, near the centre, where most of the meteorites have been found, is a crater with raised edges three-quarters of a mile in diameter and about 600 feet deep, bearing exactly the appearance which would be produced had a mighty mass of iron struck the ground and buried itself deep under the surface. Altogether, ten tons of this iron have been collected, and specimens of the Canyon Diablo meteorite are in most collectors’ cabinets.
An ardent mineralogist—the late Dr. Foote—cutting a section of this meteorite, found the tools were injured by something vastly harder than metallic iron. He examined the specimen chemically, and soon after announced to the scientific world that the Canyon Diablo meteorite contained black and transparent diamonds. This startling discovery was afterwards verified by Professors Moissan and Friedel, and Moissan, working on 183 kilogrammes of the Canyon Diablo meteorite, has recently found smooth black diamonds and transparent diamonds in the form of octahedra with rounded edges, together with green, hexagonal crystals of carbon silicide. The presence of carbon silicide in the meteorite shows that it must at some time have experienced the temperature of the electric furnace. Since this revelation the search for diamonds in meteorites has occupied the attention of chemists all over the world.
[Fig. 23 A, C, and D], are reproductions of photographs of true diamonds I myself have extracted from the Canyon Diablo meteorite.
FIG. 23. DIAMONDS FROM CANYON DIABLO METEORITE.
To face p. 138.
Under atmospheric influences the iron would rapidly oxidise and rust away, colouring the adjacent soil with red oxide of iron. The meteoric diamonds would be unaffected and left on the surface of the soil, to be found haphazard when oxidation had removed the last proof of their celestial origin. That there are still lumps of iron left at Arizona is merely due to the extreme dryness of the climate and the comparatively short time that the iron has been on our planet. We are here witnesses to the course of an event which may have happened in geologic times anywhere on the earth’s surface.
Although in Arizona diamonds have fallen from the skies, confounding our senses, this descent of precious stones is what may be called a freak of nature rather than a normal occurrence. To the modern student of science there is no great difference between the composition of our earth and that of extra-terrestrial masses. The mineral peridot is a constant extra-terrestrial visitor, present in most meteorites. And yet no one doubts that peridot is also a true constituent of rocks formed on this earth. The spectroscope reveals that the elementary composition of the stars and the earth are pretty much the same; and the spectroscope also shows that meteorites have as much of earth as of heaven in their composition. Indeed, not only are the selfsame elements present in meteorites, but they are combined in the same way to form the same minerals as in the crust of the earth.
It is certain from observations I have made, corroborated by experience gained in the laboratory, that iron at a high temperature and under great pressure—conditions existent at great depths below the surface of the earth—acts as the long-sought solvent for carbon, and will allow it to crystallise out in the form of diamond. But it is also certain, from the evidence afforded by the Arizona and other meteorites, that similar conditions have existed among bodies in space, and that on more than one occasion a meteorite freighted with jewels has fallen as a star from the sky.
[INDEX]
Able, Sir F., closed vessel experiments, [122]
Absorption spectrum of diamond, [101]
Aliwal North, [6]
Alluvial deposits of diamonds, [9]
Amygdaloidal trap, [10]
Arizona meteor, [136]
Arkansas, diamonds in, [2]
Ash of diamond, [82], [89]
Augite, [20]
Automatic diamond collector, [56]
Barytes, [71]
— density of, [93]
Basalt, [15]
Basutos, [12], [39]
Bechuanas, [12], [39]
Beryl, density of, [93]
— refractive index of, [103]
Biotite, [20]
Blackening of diamonds, [98]
Blue ground, [10], [47]
— — diamantiferous, [18], [19]
Boart, [81],
— combustion temperature of, [90]
— density of, [93]
Boiling-point of carbon, [110]
Bonney, Rev. Professor, [67]
Boyle on the diamond, [100]
Brazil, diamonds in, [4]
Breakwater, Cape Town, [36]
Breccia, diamantiferous, [19]
Brilliant cut diamond, [102]
British Association in South Africa, [7]
British Guiana, diamonds in, [4]
Bronzite, [20], [71]
— hydrated, [19]
Bultfontein Mine, [14]
— — characteristics of diamond from, [64]
Bursting of diamonds, [105]
Calcite, [20], [97]
California, diamonds in, [3]
Canada balsam, refractive index of, [103]
Canyon Diablo meteorite, [136]
Cape Colony, [5]
Cape Town, [5]
Carat, equivalent in grains, [69]
Carbon, boiling and melting point of, [110]
— combustion temperature of, [90]
— critical point of, [110]
— density of, [93]
— dissolved in iron, [116]
— volatilisation of, [115]
Carbonado, [81]
— density of, [93]
Characteristics of diamonds from the different mines, [64]
Chemical properties of diamond, [89]
Chromate of lead, refractive index of, [103]
Chrome diopside, [71]
— iron, [20]
— — ore, [71]
— — — density of, [93]
Chromite, [20]
Classification of rough diamonds, [73]
Cleavage of diamonds, [78]
Coke, density of, [93]
Colesberg Kopje, [26]
Collecting the gems, [55]
Coloured diamonds, [62], [82]
Combustion of diamond, [89]
— temperatures of diamond, boart, graphite, and carbon, [90]
“Comet” crushers, [49]
Compound system, [36], [37]
Concentrating and washing machinery, [49]
Convict labourers, [71]
Cordite, diamond from explosion of, [123]
Corundum, [20]
— density of, [93]
Cradock, [6]
Craters or pipes, [18]
Crown glass, refractive index of, [103]
Crusher, “Comet,” [49]
Crystallisation of diamond, [86]
Crystals, octahedra, of diamond, [63], [86]
Cullinan diamond, [15], [76], [80], [104]
Dallas, Captain, [40]
De Beers Consolidated Mines, [7], [33]
— — floors at Kenilworth, [47]
— — Mine, [14], [24], [34]
— — — characteristics of diamonds from, [64]
— — strong-room, [74]
Delhi diamond, [107]
Density of diamond, [57], [93]
— of graphite, [83], [93]
— of stones accompanying diamond, [70], [71], [93], [95]
Depositing floors, [46]
Dewar, Sir J., conversion of diamond into graphite, [123]
Diabase, olivine, [16]
Diallage, [20]
Diamond, absorption spectrum of, [101]
— and polarised light, [104]
— a new formation of, [122]
— ash of, [82], [89]
— collector, automatic, [56]
— combustion of, [89]
— — temperature of, [90]
— converted into graphite, [100]
— density of, [57], [93]
— etched by burning, [88]
— explosion of, [120]
— genesis of the, [115]
— in meteors, [134]
— in Röntgen rays, [107]
— matrix of, [67]
— natural formation of, [127]
— Office at Kimberley, [73]
— physical and chemical properties of, [89]
— pipes or craters, [18]
— radio-activity of, [109]
— refractive index of, [103]
— Trade Act, [36]
— triangular markings on, [87]
— tribo-luminescence of, [100]
Diamonds, coloured or fancy, [62], [82]
— Maskelyne on, [1]
— noteworthy, [76]
— phosphorescence of, [96]
— produced, weight, value of, [35]
— yield of, from De Beers, [60]
Drift, diamonds from the, [12]
Duke of Tuscany diamond, [80]
Dutch boart, or zircon, [59]
Dutoitspan Mine, [14], [23]
— — characteristics of diamonds from, [64]
Eclogite, [20]
— containing diamonds, [67]
Electrons, bombardment by, [98]
Emerald, refractive index of, [103]
Empress Eugenie diamond, [80]
Enstatite, [20]
Explosion of diamonds, [120]
Excelsior diamond, [80]
Fancy stones, [62]
Fingoes, [39]
Flint glass, refractive index of, [103]
“Floating Reef,” [21]
Floors, depositing, [46]
Fluor-spar, refractive index of, [103]
Formation, new, of diamond, [122]
Fort Beaufort, [6]
Franklinite, [97]
Frank Smith Mine, [15]
— — — characteristics of diamonds from, [66]
Fraserburg, [6]
Garnet, [20], [70]
— density of, [93]
Genesis of the diamond, [115]
“Golden fancies,” [65]
Granite, [18]
— density of, [93]
Graphite, [81], [83]
— combustion temperature of, [90]
— conversion of diamond into, [100]
— density of, [93]
— diamonds coated with, [99]
Graphitic oxide, [83], [93]
Grease, collecting diamonds by aid of, [57]
Hard blue ground, [47]
Hardness of diamond, [90]
Haulage system, [46]
Hexakis-octahedron crystal, [86]
Hope blue diamond, the, [80]
Hornblende, [71]
— density of, [93]
Iceland spar, refractive index of, [103]
Ice, refractive index of, [103]
I.D.B. laws (Illicit Diamond Buying), [36]
Ilmenite, [20]
India, diamonds in, [4]
Inverel diamonds, [91]
Internal strain in diamonds, [104]
Iron a solvent for carbon, [116]
— ore, density of, [93]
— pyrites, [20]
Jagersfontein diamond, [79]
— Mine, [14]
— — characteristics of diamonds from, [68]
Jeffreysite, [20]
Kafirs, [42]
Kamfersdam Mine, [15]
— — characteristics of diamonds from, [66]
Kenilworth depositing floors, [47]
Kimberley, [6]
— blue ground, [10]
— mines, [14], [23], [34]
— Mine in old days, [25]
— — at the present day, [34]
— — characteristics of diamonds from, [63]
— shales, [15]
— West Mine, [15]
— — — characteristics of diamonds from, [66]
Kirsten’s automatic diamond collector, [57]
Klipdam, [8], [23]
Koffyfontein Mine, [14]
Koh-i-noor diamond, [80]
— hardness of, [91]
Kyanite, [20], [71]
Lamp, ultra-violet, [97]
Leicester Mine, [15], [23]
— — characteristics of diamonds from, [67]
Loterie d’Angleterre diamond, [80]
Lustre of rough diamonds, [56]
Machinery for washing and concentrating, [49]
Macles, [86]
Magnetite, [20], [71]
— density of, [93]
Maskelyne on diamonds, [1]
Matabele, [12], [39]
Matrix of diamond, [67]
Melaphyre, [10], [16]
Melting-point of carbon, [110]
Meteor, Canyon Diablo, [136]
Meteoric diamonds, [134]
Meydenbauer on meteoric diamonds, [135]
Mica, [20], [71]
— density of, [93]
Moissan’s experiments on the genesis of diamond, [115]
Mud volcano, [24]
Nassak diamond, [80]
Natal, coal in, [6]
Natural formation of diamond, [127]
Newlands Mine, [15]
— — characteristics of diamonds from, [67]
New Rush diggings, [26]
Nizam of Hyderabad diamond, [80]
Noble, Sir A., experiments, [122], [131]
Noteworthy diamonds, [76]
Octahedral crystals of diamond, [63], [86]
Olivine, [20]
— diabase, [16]
Orange River Colony, coal in, [6]
— — — diamonds in, [14]
Orloff diamond, [80]
Pasha of Egypt diamond, [80]
Paterson, Mr., description of Kimberley in old days, [25]
Peridot, [20], [139]
Peridotite, [3]
Perofskite, [20]
Phosphorescence of diamonds, [96]
Phosphorus, refractive index of, [103]
Physical properties of diamond, [89]
Picking tables, [51]
Pipes or craters, [18]
Pitt diamond, [80]
Polarised light and diamond, [104]
Pole Star diamond, [80]
Pondos, [39], [42]
Premier Mine, [15], [76]
Prodigious diamonds, [76]
Pseudobrookite, [20]
Pulsator, [52]
Pyrope, [70]
Quartzite, [16], [20]
— density of, [93]
— refractive index of, [103]
Radio-activity of diamond, [109]
Radium, action on diamond, [108]
“Reef,” [21]
Refractive indices, [103]
Refractivity of diamond, [102]
Regent diamond, [80]
Reunert, Mr., description of Kimberley Mine, [30]
Rhodes, Cecil John, [34]
River washings, [7]
Rock shafts, [43]
Röntgen rays, diamond in, [107]
Ruby, refractive index of, [103]
Rutile, [20]
Sahlite, [20]
Sancy diamond, [80]
Savings of the native workmen, [41]
Scalenohedron diamond crystal, [86]
Serpentine, [19]
Shafts, rock, [43]
Shah diamond, [80]
Shales, Kimberley, [15]
Shangains, [39]
Shells in blue ground, [21]
Shot boart, [81]
Silver and thallium, nitrate of, [94]
Smaragdite, [20]
Soft blue ground, [47]
Sorting the diamantiferous gravel, [55]
Specific gravity, see Density
Spectrum, absorption of diamond, [101]
Sphalerite, [100]
Spinthariscope, [108]
Sprat’s History of the Royal Society, [1]
Sprouting graphite, [84]
Star of the South diamond, [80]
Stones other than diamonds, [70], [71], [93], [95]
Strain, internal, in diamonds, [104]
Sulphur, refractive index of, [103]
Swazis, [39]
Ultra-violet lamp to show phosphorescence, [97]
Underground workings, [43]
United States, diamonds in, [2]
Vaalite, [20]
Vaal River, [8], [16]
Valuators, [73]
Value of diamonds per carat, [12], [69]
Value of diamonds, progressive increase in, [69]
Vermiculite, [20]
Volatilisation of carbon, [115]
Volcanic necks, [18]
Volcano, mud, [24]
Wages, scale of, [35]
Washing and concentrating machinery, [49]
Wesselton Mine, [14], [15], [23], [35]
— — characteristics of diamonds from, [65]
Willemite, [97]
Wollastonite, [20]
Workings, underground, [43]
Yellow ground, diamantiferous, [19]
Yield of diamonds, annual, [60]
— — — total, [35]
— falls off with depth, [68]
— per load of blue ground, [62]
Zimbabwe ruins, [40]
Zircon, [20], [59], [71]
— density of, [93]
Zulus, [12], [39], [40]
W. BRENDON AND SON, LTD., PRINTERS, PLYMOUTH
[FOOTNOTES:]
[1] Chemical News, Vol. I, p. 208.
[2] Mr. Paterson called “limey stuff” what is now termed “blue ground.” It was also formerly called “marl stuff,” “blue stuff,” and “blue clay.”
[3] The original name for the Kimberley Mine. It was also sometimes known as “Colesberg Kopje.”
[4] Diamonds and Gold in South Africa. By T. Reunert. Johannesburg, 1893.
[5] According to Gardner Williams the South African carat is equivalent to 3·174 grains. In Latimer Clark’s Dictionary of Metric and other Useful Measures the diamond carat is given as equal to 3·1683 grains = 0·2053 gramme = 4 diamond grains; 1 diamond grain = 0·792 troy grain; 151·5 diamond carats = 1 ounce troy.
Webster’s International Dictionary gives the diamond carat as equal to 3⅕ troy grains.
The Oxford English Dictionary says the carat was originally 1/144 of an ounce, or 3⅓ grains, but now equal to about 3⅕ grains, though varying slightly with time and place.
The Century Dictionary says the diamond carat is equal to about 3⅙ troy grains, and adds that in 1877 the weight of the carat was fixed by a syndicate of London, Paris, and Amsterdam jewellers at 205 milligrammes. This would make the carat equal to 3·163 troy grains. A law has been passed in France ordaining that in the purchase or sale of diamonds and other precious stones the term “metric carat” shall be employed to designate a weight of 200 milligrammes (3·086 grains troy), and prohibiting the use of the word carat to designate any other weight.
[6] Artificial tribo-luminescent sphalerite:—
| Zinc carbonate | 100 parts |
| Flower of sulphur | 30 ” |
| Manganese sulphate | ½ per cent. |
Mix with distilled water and dry at a gentle heat. Put in luted crucible and keep at a bright red heat for from two to three hours.
[7] Sir James Dewar, in a Friday evening discourse at the Royal Institution in 1880, showed an experiment proving that the temperature of the interior of a carbon tube heated by an outside electric arc was higher than that of the oxy-hydrogen flame. He placed a few small crystals of diamond in the carbon tube, and, maintaining a current of hydrogen to prevent oxidation, raised the temperature of the tube in an electric furnace to that of the arc. In a few minutes the diamond was transformed into graphite. At first sight this would seem to show that diamond cannot be formed at temperatures above that of the arc. It is probable, however, for reasons given above, that at exceedingly high pressures the result would be different.
[8] The silica was in the form of spheres, perfectly shaped and transparent, mostly colourless, but among them several of a ruby colour. When 5 per cent of silica was added to cordite, the residue of the closed vessel explosion contained a much larger quantity of these spheres.
[9] A pressure of fifteen tons on the square inch would exist not many miles beneath the surface of the earth.
[10] There are abundant signs that a considerable portion of this part of Africa was once under water, and a fresh-water shell has been found in apparently undisturbed blue ground at Kimberley.
[11] The water sunk in wells close to the Kimberley mine is sometimes impregnated with paraffin, and Sir H. Roscoe extracted a solid hydrocarbon from the “blue ground.”
[12] Chemical News, vol. lxi, p. 209, 1890.
TRANSCRIBER’S NOTE
Obvious typographical errors and punctuation errors have been corrected after careful comparison with other occurrences within the text and consultation of external sources.
All misspellings in the text, and inconsistent or archaic usage, have been retained: for example, unfrequent; clayey; friable; slaty; imbed; stoped; peculation; situate.
In the [Table of Contents], the Index page number ‘145’ has been replaced by ‘141’.
In the [Index], ‘Colesberg Copje’ has been replaced by ‘Colesberg Kopje’, and ‘DeBeers’ has been replaced by ‘De Beers’.