NATURE 



[August 5, 1897 



detected and distinguished from the true gems. It would take 

 a good observer to distinguish my pure triangular diamond from 

 the adjacent glass imitation. 



Genesis of the Diamond. 



Speculations as to the probable origin of the diamond have 

 been greatly forwarded by patient research, and particularly by 

 improved means of obtaining high temperatures. Thanks to the 

 success of Prof. Moissan, whose name will always be associated 

 with the artificial production of diamonds, we are able to-day to 

 manufacture diamonds in our laboratories— minutely microscopic, 

 it is true — all the same veritable diamonds, with crystalline form 

 and appearance, colour, hardness, and action on light the same 

 as the natural gem. 



Until recent years carbon was considered absolutely non- 

 volatile and infusible ; but the enormous temperatures at the 

 disposal of experimentalists — by the introduction of electricity — 

 show that, instead of breaking rules, carbon obeys the same laws 

 that govern other bodies. It volatilises at the ordinary pressure 

 at a temperature of about 3600° C, and passes from the solid to 

 the gaseous state without liquefying. It has been found that 

 other bodies which volatilise without liquefying at the ordinary 

 pressure will easily liquefy if pressure is added to temperature. 

 Thus, arsenic liquefies under the action of heat if the pressure is 

 increased ; it naturally follows that if along with the requisite 

 temperature sufficient pressure is applied, liquefaction of carbon 

 will be likely to take place, when on cooling it will crystallise. 

 But carbon at high temperatures is a most energetic chemical 

 agent, and if it can get hold of oxygen from the atmosphere or 

 any compound containing it, it will oxidise and fly off in the 

 forrn of carbonic acid. Heat and pressure, therefore, are of no 

 avail unless the carbon can be kept inert. 



It has long been known that iron when melted dissolves car- 

 bon, and on cooling liberates it in the form of graphite. Moissan 

 discovered that several other metals have similar properties, 

 especially silver ; but iron is the best solvent for carbon. The 

 quantity of carbon entering into solution increases with the 

 temperature, and on cooling in ordinary circumstances it is 

 largely deposited as crystalline graphite. 



Prof. Dewar has made a calculation as to the critical pressure 

 of carbon — that is, the lowest pressure at which carbon can be 

 got to assume the liquid state at its critical temperature, that is 

 the highest temperature at which liquefaction is possible. He 

 starts from the vaporising or boiling point of carbon, which, 

 from the experiments of Violle and others on the electric arc, is 

 about 3600 €., or 3874° Absolute. The critical point of a 

 substance on the average is i -5 times its absolute boiling point. 

 Therefore the critical point of carbon is 5811° Ab. , or, say, 

 5800° Ab. But the absolute critical temperature divided by the 

 critical pressure is for elements never less than 2 "5. Then — 



5800° A. „,- qSoo" A. 



^ — = 2"5, or PCr = A- — — , or 2320 atmospheres. 



The result is that the critical pressure of carbon is about 2300 

 atmospheres, or, say, 15 tons on the square inch. The highest 

 critical pressure recorded is that of water, amounting to 195 

 atmospheres, and the lowest that of hydrogen, about 20 atmo- 

 spheres. In other words, the critical pressure of water is ten 

 times that of hydrogen, and the critical pressure of carbon is ten 

 times that of water. 



Now, 15 tons on the square inch is not a difficult pressure to 

 obtain in a closed vessel. 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. 

 Here, then, if the observations are correct, we have sufficient 

 temperature and enough pressure to liquefy carbon ; and if the 

 temperature could only be allowed to act for a sufficient time on 

 the carbon, there is little doubt that the artificial formation of 

 diamonds would soon pass from the microscopic stage to a scale 

 more likely to satisfy the requirements of science, industry, and 

 personal decoration. 



Artificial Manufacture of the Diamond. 

 I will now proceed to manufacture a diamond before your 

 eyes — don't think I yet have a talisman that will make me rich 

 beyond the dreams of avarice ! Hitherto the results have been 

 very microscopic, and are chiefly of scientific interest in showing 

 us nature's workshop, and how we may ultimately hope to vie 

 with her in the manufacture of diamonds. Unfortunately, the 



NO. 1449, VOL. 56] 



operations of separating the diamond from the iron and other 

 bodies with which it is associated are somewhat prolonged — 

 nearly a fortnight being required to detach it from the iron, 

 graphite, and other matters in which it is embedded. I can, 

 however, show the different stages of the operations, and project 

 on the screen diamonds made in this manner. 



In Paris, recently, I saw the operation carried out by M. 

 Moissan, the discoverer of this method of making carbon 

 separate out in the transparent crystalline form, and I can show 

 you the operations straight, as it were, from the inventor's 

 laboratory. I am also indebted to the Directors of the Notting 

 Hill Electric Lighting Co. and to the General Manager, Mr. 

 Schultz, for enabling me to perform several operations at their 

 central station, where currents of 500 amperes and loo volts. 

 were placed at my disposal. 



The first necessity is to select pure iron — free from sulphur, 

 silicon, phosphorus, &c. — and to pack it in a carbon crucible 

 with pure charcoal from sugar. Half a pound of this iron is- 

 then put into the body of the electric furnace, and a powerful! 

 arc formed close above it between carbon poles, utilising a 

 current of 800 amperes at 40 volts pressure. The iron rapidly 

 melts and saturates itself with carbon. After a few minutes*^ 

 heating to a temperature above 4000° C. — a temperature at 

 which the lime of the furnace melts like wax and volatilises in 

 clouds— the current is stopped, and the dazzling fiery crucible 

 is plunged beneath the surface of cold water, where it is held 

 till it sinks below a red heat. As is well known, iron increases 

 in volume at the moment of passing from the liquid to the 

 solid state. The sudden cooling solidifies the outer layer of 

 iron, and holds the inner molten mass in a tight grip. The 

 expansion of the inner liquid on solidifying produces an enor- 

 mous pressure, and under the stress of this pressure the dis- 

 solved carbon separates out in a transparent, dense, crystalline 

 form — in fact, as diamond. 



Now' commences the tedious part of the process. The 

 metallic ingot is attacked with hot nitro-hydrochloric acid until 

 no more iron is dissolved. The bulky residue, consisting 

 chiefly of graphite, together with translucent flakes of a chest- 

 nut-coloured carbon, black opaque carbon of a density of from 

 3"0 to 3*5, and hard as diamonds — black diamonds or carbonado, 

 in fact, and a small portion of transparent colourless diamonds 

 showing crystalline structure. Besides these, there may be 

 carbide of silicon and corundum, arising from impurities in the 

 materials employed. 



The residue is first heated for some hours with strong sul- 

 phuric acid at the boiling point, with the cautious addition of 

 powdered nitre. It is then well washed and allowed for two 

 days to soak in strong hydrofluoric acid in the cold, then in 

 boiling acid. After this treatment the soft graphite will dis- 

 appear, and most, if not all, of the silicon compounds will be 

 destroyed. Hot sulphuric acid is again applied to destroy the 

 fluorides, and the residue, well washed, is repeatedly attacked 

 with a mixture of the strongest nitric acid and powdered 

 potassium chlorate, kept warm, but to avoid explosions not 

 above 60° C. This ceremony must be repeated six or eight 

 times, when all the hard graphite will gradually be dissolved, 

 and little else left but graphitic oxide, diamond, and the harder 

 carbonado and boart. The residue is fused lor an hour in 

 fluorhydrate of fluoride of potassium, then boiled out in water, 

 and again heated in sulphuric acid. The well-washed grains 

 which resist this energetic treatment are dried, carefully de- 

 posited on a slide, and examined under the microscope. 

 Along with numerous pieces of black diamond are seen trans- 

 parent colourless pieces, some amorphous, others with a crystal- 

 line appearance, as I have attempted to reproduce in diagrams. 

 Although many fragments of crystals occur, it is remarkable 

 that I have never seen a complete crystal. All appear broken 

 up, as if on being liberated from the intense pressure under 

 which they were formed they burst asunder. I have direct 

 evidence of this phenomenon. A very fine piece of artificial 

 diamond, carefully mounted by me on a microscopic slide, 

 exploded during the night, and covered my slide with fragments. 

 This bursting paroxysm is not unknown at the Kimberley 

 mines. 



On the screen I will project fragments of artificial diamond, 

 some lent me by Prof. Roberts-Austen, others of my own 

 make ; while on the wall you will see drawings of diamonds 

 copied from M. Moissan's book on the electric furnace. Un- 

 fortunately these specimens are all microscopic. The largest 

 artificial diamond, so far, is less than one millimetre across. 



