Graphite Sentence Examples

The massive graphite is very easily machined and is widely used for electrodes, dynamo brushes, lead pencils and the like.

Graphite and some silver ores have also been found.

It is a black crystalline powder, resembling graphite in appearance.

Wotton's letter of 1620, already noted, was not published till 1651 (Reliquiae Wottonianae, p. 141), but in 1658 a description of Kepler's portable tent camera for sketching, taken from it, was published in a work called Graphite, or the most excellent Art of Painting, but no mention is made of Kepler.

Its other mineral resources include graphite, copper, zinc, lead, salt, alum, potter's clay, marble and good mill and building stones.

The Cumberland graphite, which is especially suitable for pencils, contains about 12% of impurities.

Graphite is present in Buganda and Unyoro.

Graphite is black and opaque, whilst diamond is colourless and transparent; it is one of the softest (H= I) of minerals, and diamond the hardest of all; it is a good conductor of electricity, whilst diamond is a bad conductor.

Besides the above, the mineral resources of Mexico include coal, petroleum, asphalt, platinum, graphite, soda and marble.

Troost produced crystallized zirconium by fusing the double fluoride with aluminium in a graphite crucible at the temperature of melting iron, and extracting the aluminium from the melt with hydrochloric acid.

See "Graphite and its Uses," Bull.

The charge is completely melted in about half an hour, and it is then thoroughly mixed by stirring with a graphite rod.

Graphite is used for the manufacture of pencils, dry lubricants, grate polish, paints, crucibles and for foundry facings.

Deposits of copper, tin, iron and tungsten have been discovered, and a variety of other mineral products (graphite, mica, spodumene, coal, petroleum, &c.).

A little graphite is produced in Humboldt county.

These chemists electrolyse either pure calcium chloride, or a mixture of this salt with fluorspar, in a graphite vessel which servos as the anode.

The lustre is bright and metallic. In its external characters graphite is thus strikingly similar to molybdenite.

But beyond this are the very useful, because very fusible, cast irons with from 3 to 4% of carbon, the embrittling effect of which is much lessened by its being in the state of graphite.

As these flakes readily split open, when a piece of this iron is broken rupture passes through them, with the result that, even though the graphite may form only some 3% of the mass by weight (say to% by volume), practically nothing but graphite is seen in the fracture.

Hence the weakness and the dark-grey fracture of this iron, and hence, by brushing this fracture with a wire brush and so detaching these loosely clinging flakes of graphite, the colour can be changed nearly to the very light-grey of pure iron.

There is rarely any important quantity of graphite in commercial steels.

Double Nature of the Carbon-Iron Diagram.-The part played by graphite in the constitution of the iron-carbon compounds, hitherto ignored for simplicity, is shown in fig.

In it the normal constituents are, for region II., molten metal+primary austenite; for region III., molten metal+primary graphite; for region IV., primary austenite; for region VII., eutectic austenite, eutectic graphite, and a quantity of pro-eutectoid graphite which increases as we pass from the upper to the lower part of the region, together with primary austenite at the left of the eutectic point B' and primary graphite at the right of that point.

Though carbon passes far more readily under most conditions into the state of cementite than into that of graphite, yet of the two graphite is the more stable and cementite the less stable, or the ' metastable " form.

Thus cementite is always tending to change over into graphite by the reaction Fe C = 3Fe +Gr, though this tendency is often held in check by different causes; but graphite never changes back directly into cementite, at least according to our present theory.

The fact that graphite may dissolve in the iron as austenite, and that when this latter again breaks up it is more likely to yield cementite than graphite, is only an apparent and not a real exception to this law of the greater stability of graphite than of cementite.

Slow cooling, slow solidification, the presence of an abundance of carbon, and the presence of silicon, all favour the formation of graphite; rapid cooling, the presence of sulphur, and in most cases that of manganese, favour the formation of cementite.

For instance, though in cast iron, which is rich in carbon, that carbon passes comparatively easily into the state of graphite, yet in steel, which contains much less carbon, but little graphite forms under most conditions.

Indeed, in the common structural steels which contain only very little carbon, hardly any of that carbon exists as graphite.

The joint effect of such chilling and such annealing is to make the metal much harder than if slowly cooled, because for each 1% of graphite which the chilling suppresses, 15% of the glass-hard cementite is substituted.

The molecular freedom which this high temperature gives enables the cementite to change gradually into a mixture of graphite and austenite with the result that, after the castings have been cooled and their austenite has in cooling past Aci changed into pearlite and ferrite, the mixture of cementite and pearlite of which they originally consisted has now given place to one of fine or " temper " graphite and ferrite, with more or less pearlite according to the completeness of the transfer of the carbon to the state of graphite.

The reason is that the particles of temper graphite which are thus formed within the solid casting in its long annealing are so finely divided that they do not break up the continuity of the mass in a very harmful way; whereas in grey cast iron both the eutectic graphite formed in solidifying, and also the primary graphite which, in case the metal is hypereutectic, forms in cooling through region 3 of fig.

In carrying out this process the castings are packed in a mass of iron oxide, which at this temperature gradually removes the fine or " temper " graphite by oxidizing that in the outer crust to carbonic oxide, whereon the carbon farther in begins diffusing outwards by " molecular migration," to be itself oxidized on reaching the crust.

This removal of graphite doubtless further stimulates the formation of graphite, by relieving the mechanical and perhaps the osmotic pressure.

Thus, first, for the brittle glass-hard cementite there is gradually substituted the relatively harmless temper graphite; and, second, even this is in part removed by surface oxidation.

In the former case there is no later chance to remove sulphur, a minute quantity of which does great harm by leading to the formation of cementite instead of graphite and ferrite, and thus making the cast-iron castings too hard to be cut to exact shape with steel tools; in the latter case the converting or purifying processes, which are essentially oxidizing ones, though they remove the other impurities, carbon, silicon, phosphorus and manganese, are not well adapted to desulphurizing, which needs rather deoxidizing conditions, so as to cause the formation of calcium sulphide, than oxidizing ones.

Indeed this high carbon-content, 3 to 4%, in practice actually leads to less brittleness than can readily be had with somewhat less carbon, because with it much of the carbon can easily be thrown into the relatively harmless state of graphite, whereas if the carbon amounts to less than 3% it can be brought to this state only with difficulty.

Of these several qualities which cast iron may have, fluidity is given by keeping the sulphur-content low and phosphoruscontent high; and this latter element must be kept low if shock is to be resisted; but strength, hardness, endurance of shock, density and expansion in solidifying are controlled essentially by the distribution of the carbon between the states of graphite and cementite, and this in turn is controlled chiefly by the proportion of silicon, manganese and sulphur present, and in many cases by the rate of cooling.

This carbon may all be present as graphite, as in typical grey cast iron; or all present as cementite, Fe 3 C, as in typical white cast iron; or, as is far more usual, part of it may be present as graphite and part as cementite.

If this carbon is all present as graphite, so that in cooling the graphite-austenite diagram has been followed strictly (§ 26), the constitution is extremely simple; clearly the mass consists first of a metallic matrix, the carbonless iron itself with whatever silicon, manganese, phosphorus and sulphur happen to be present, in short an impure ferrite, encased in which as a wholly distinct foreign body is the graphite.

The primary graphite (§ 26) generally forms a coarse, nearly continuous skeleton of curved black plates, like those shown in fig.

We must grasp clearly this conception of metallic matrix and encased graphite skeleton if we are to understand this subject.

Next let us imagine that, in a series of cast irons all containing 4% of carbon, the graphite of the initial skeleton changes gradually into cementite and thereby becomes part of the matrix, a change which of course has two aspects, first, a gradual thinning of the graphite skeleton and a decrease of its continuity, and second, a gradual introduction of cementite into the originally pure ferrite matrix.

By the time that 0.4% of graphite has thus changed, and in changing has united with o 4 X14 =5.6% of!

The mass as a whole, then, consists of 96.4 parts of metallic matrix, which itself is in effect a 0.415% carbon rail steel, weakened and embrittled by having its continuity broken up by this skeleton of graphite forming 3.6% of the whole mass by weight, or say 12% by volume.

As, in succeeding members of this same series of cast irons, more of the graphite of the initial skeleton changes into cementite and thereby becomes part of the metallic matrix, so the graphite skeleton becomes progressively thinner and more discontinuous, and the matrix richer in cementite and hence in carbon and hence equivalent first to higher and higher carbon steel, such as tool steel of I carbon, file steel of 1.50%, wire-die steel of 2% carbon and then to white cast iron, which consists essentially of much cementite with little ferrite.

Above the diagram are given the names of the different classes of cast iron to which different stages in the change from graphite to cementite correspond, and above these the names of kinds of steel or cast iron to which at the corresponding stages the constitution of the matrix corresponds, while below the diagram are given the properties of the cast iron as a whole corresponding to these stages, and still lower the purposes for which these stages fit the cast iron, first because of its strength and shock-resisting power, and second because of its hardness.

Influence of the Constitution of Cast Iron on its Properties.- How should the hardness, strength and ductility, or rather shockresisting power, of the cast iron be affected by this progressive change from graphite into cementite ?

First, the hardness (VU) should increase progressively as the soft ferrite and graphite are replaced by the glass-hard cementite.

Second, though the brittleness should be lessened somewhat by the decrease in the extent to which the continuity of the strong matrix is broken up by the graphite skeleton, yet this effect is outweighed greatly by that of the rapid substitution in the matrix of the brittle cementite for the' very ductile copper-like ferrite, so that the brittleness increases continuously (RS), from that of the very grey graphitic cast irons, which, like that of soapstone, is so slight that the metal can endure severe shock and even indentation without breaking, to that of the pure white cast iron which is about as brittle as porcelain.

Here let us recognize that what gives this transfer of carbon from graphite skeleton to metallic matrix such very great influence on the properties of the metal is the fact that the transfer of each 1%.

Hence, as with the progressive transfer of the carbon from the graphitic to the cementite state in our imaginary series of cast irons, the combined carbon present in the matrix increases, so does the tensile strength of the mass as a whole for two reasons; first, because the strength of the matrix itself is increasing (DE), and second, because the discontinuity is decreasing with the decreasing proportion of graphite.

With further transfer of the carbon from the graphitic to the combined state, the matrix itself grows weaker (EF); but this weakening is offset in a measure by the continuing decrease of discontinuity due to the decreasing proportion of graphite.

As regards both tensile strength and ductility not only the quantity but the distribution of the graphite is of great importance.

Thus it is extremely probable that the primary graphite, which forms large sheets, is much more weakening and embrittling than the eutectic and other forms, and therefore that, if either strength or ductility is sought, the metal should be free from primary graphite, i.e..

The presence of graphite has two further and very natural effects.

To sum this up, as graphite is replaced by carbon combined as cementite, the hardness, brittleness and density increase, and the expansion in solidification decreases, in both cases continuously, while the tensile strength increases till the combined carbon-content rises a little above I %, and then in turn decreases.

Hence objects which need much machining are made rich in graphite, so that gressively from the state of graphite to that of cementite as we pass they may be cut easily, and those of the latter class rich in from specimen to specimen, may, with the foregoing picture of a cementite so that they may not wear out.

The change from graphite into cementite is supposed to distribution of the carbon between these two states, so as to give take place as we pass from left to right.

Beyond this, rapid cooling and the presence of sulphur both oppose the formation of graphite, and hence in cast iron rich in sulphur, and in thin and therefore rapidly cooling castings, the silicon-content must be greater than in thick ones and in those freer from sulphur.

Castings which, like hydraulic press cylinders and steam radiators, must be dense and hence must have but little graphite lest their contents leak through their walls, should not have more than 1.75% of silicon and may have even as little as 1% if impenetrability is so important that softness and consequent ease of machining must be sacrificed to it.

In the case of the quadrivalent carbon, diamond seems to be the stable form at ordinary temperatures, but one may wait long before it is formed from graphite.

Its physical and chemical properties have been the subject of much study, and have a special interest in view of the extraordinary difference between the physical characters of the diamond and those of graphite (blacklead) or charcoal, with which it is chemically identical, and into which it can be converted by the action of heat or electricity.

The black coloration upon the surface produced by this process, as also by the electric bombardment in a vacuum tube, appears to be due to a conversion of the surface film into graphite.

It is, however, infusible at the temperature of the electric arc, but becomes converted superficially into graphite.

Wolff, who have obtained it by dissolving graphite in a fused mixture of silicates having approximately the composition of the blue ground.

The cast-iron contained nearly 3% each of silicon and graphite, and 1% each of phosphorus and manganese.

Of other minerals (with the exceptions of coal, iron and salt treated below) nickel and antimony are found in the upper Harz; cobalt in the hilly districts of Hesse and the Saxon Erzgebirge; arsenic in the Riesengebirge; quicksilver in the Sauerland and in the spurs of the Saarbrucken coal hills; graphite in Bavaria; porcelain clay in Saxony and Silesia; amber along the whole Baltic coast; and lime and gypsum in almost all parts.

From these rocks in the Ottawa valley are quarried or mined granite, marble, magnificent blue sodalite, felspar, talc, actinolite, mica, apatite, graphite and corundum; the latter mineral, which occurs on a larger scale here than elsewhere, is rapidly replacing emery as an abrasive.

Silver, copper, lead and iron are worked to some profit, while arsenic, alum, graphite, marble, porcelain, precious and building stones are also found.

Other mineral products are graphite, garnet used as an abrasive, pyrite and zinc ore.

Iron ores are widely distributed, but have not been developed; graphite is mined in Colfax county; mica in Taos county, and to a small extent in Rio Arriba county; marble is quarried in Otero county and sandstone in Bernalillo, Colfax and San Miguel counties.

Lignite and coal, some graphite and kaolin, are mined, as also amber, which is often found in big lumps.

The chief impurities are basic salts of iron, free iron, graphite, and sometimes silica, antimony and iron arsenates.

The rock has a prevalent grey colour, and contains as characteristic minerals garnet and in some parts graphite.

Antimony is extracted at Milleschau near Tabor; uranium and radium near Joachimsthal; graphite near Krumau and Budweis; porcelain-earth near Carlsbad.

Other minerals, which are not found in commercial quantities, are lead in the form of galena, in Sussex county; graphite, in the crystalline schistose rocks of the Highlands; molybdenum, in the form of a sulphide, in Sussex county; and barytes in Mercer and Sussex counties.

Copper, gold alloyed with platinum, iron ore, barytes, graphite and lead occur in small quantities in the state.

The petroleum wells of Ferghana and the beds of graphite about Zairamnor are neglected.

Nickel, mercury, manganese, graphite, marble, sulphur and oil shales are found in various regions, but the mineral resources of the country, as a whole, remain almost undeveloped.

Volcanic activity in the neighbourhood is further shown by the quantities of pumice-stone drifted on to the south coasts of Kandavu and Viti Levu; malachite, antimony and graphite, gold in small quantities, and specular iron-sand occur.

Minerals which were not mined commercially in 1902 include asbestos, which occurs in Spartanburg and Pickens counties; fullers'-earth; graphite in Spartanburg and Greenville counties; iron ores in the north and north-west portions of the state; iron pyrites in Spartanburg and York counties; talc, bismuth, ochre, pyrites, ' galena, brown coal, malachite, phosphate of lead and barytes.

Bitumen and petroleum have been found; graphite is plentiful, and sulphur, salt, saltpetre and lime are also procured.

Iron ores (60 to 70% of iron), copper ores, colours, brown coal, graphite, slate, and lithographic stone are obtained - nearly 2,000,000 tons of iron ore annually.

Among such substances are fireclay and firebricks, certain sandstones, silica in the form of ganister, and Dinas stone and bricks, ferric oxide and alumina, carbon (as coke and graphite), magnesia, lime and chromium oxide - their relative importance being indicated by their order, the last two or three indeed being only of limited use.

Coke dust or graphite is used for the same purpose in crucible making (see Firebrick).

Plumbago or graphite is largely used in the production of crucibles, not in the pure state but in admixture with fireclay; the proportion of the former varies with the quality from 25 to nearly 50%.

It was fitted with a high quality graphite shaft for extra distance.

The material retains the nodular graphite distribution of ductile iron, but the matrix is acicular ferrite in a high carbon austenite.

The primary standard used for this service is a graphite calorimeter and so absorbed dose calibrations must be converted from graphite to water.

A variety of dosimetry techniques are available, including graphite calorimetry, diode and ion chamber dosimetry.

Carbon nanotubes are graphite sheets of carbon nanotubes are graphite sheets of carbon which are rolled up to form tubes.

Other minerals present include diopside, pargasite, spinel, phlogopite, apatite, graphite, pyrrhotite and zircon (Davidson 1943 ).

Crown alignment aids correct set-up to the ball GOLF BAG 8 inch fur lined graphite friendly top with 6 way full length dividers.

Molded cured elastomers can also be supplied with conductive filler materials, such as silver, copper, nickel and graphite.

The feed oxide is melted using graphite electrodes which then is allowed to solidify into a large block.

Graphite is a stable and permanent material but can easily be removed using an eraser.

Arc furnace A steel melting furnace in which heat is generated by an arc between graphite electrodes and the metal.

Slightly heavier rods either contain more graphite or some glass fiber that greatly enhances their ability to stand up to some abuse.

The former includes graphite as flakes and the latter includes graphite in spherical or nodular form.

Pencil You can only use graphite (' lead ') pencils here.

This PhD project aims to develop mechanistic models for the prediction of irradiated behavior in nuclear graphite.

This is the way graphene molecules were " extracted " from bulk graphite.

Mg (Magnesium) Converts flake graphite to spheroidal graphite giving strength & ductility.

You show a pencil and point out it is carbon graphite.

Fitted with exclusive 100% low torque graphite shafts generating high club head speed.

At present irradiated graphite properties are based on empirical data obtained on samples irradiated in a material test reactor (MTR ).

Scanning electron micrograph of a fallen mesa of graphite.

The majority of her portrait commissions come from America and she specializes in the mediums graphite pencil, colored pencil and oils.

This was the birth of the graphite racket and when rackets became a lot lighter but maintained a small head like the wooden rackets.

After about 3 miles this gives way to crystalline schist 's, mainly mica and some very black graphite.

Graphite reduces the MP-001 crown weight by over 65% allowing a thicker, heavy titanium soleplate and heel.

The " tread " or circumferential part of the mould itself is made of iron, because this, by conducting the heat away from the casting rapidly, makes it cool quickly, and thus causes most of the carbon here to form cementite, and thus in turn makes the tread of the wheel intensely hard; while those parts of the mould which come in contact with the central parts of the wheel are made of sand, which conducts the heat away from the molten metal so slowly that it solidifies slowly, with the result that most of its carbon forms graphite, and here the metal is soft and shock-resisting.

Once diamond is formed, therefore, it cannot reconvert back to graphite because the barrier is too high.

The NanoTest was used to investigate diamond-like carbon films on silicon which were prepared by magnetron sputtering from a graphite target.

Steel shafts are heavier than graphite, but are more sturdy and you can worry less about cosmetic damage.

Graphite clubs are lighter, but less durable.

When you're trying to determine how to buy a hybrid golf club, one of the main things you'll need to keep in mind is whether you would prefer a steel or graphite shaft.

Most golf club shafts are made from either graphite or steel.

Steel shafted golf clubs are usually less expensive but heavier, while graphite is lighter and more expensive.

Graphite shafts offer better vibration absorption and they're easier to swing, so they're usually preferred by the average golfer whereas steel shafted clubs are typically the club of choice for the pros.

Goggles Direct has Rose Platinum lenses available with black, silver, pink, and graphite frames.

This blender has a graphite finish with colorful mango accents and controls that are oversized.

It is made from Damier graphite canvas and is masculine and modern.

It comes in graphite and tropic pink or white and mantis, a minty green.

These colors include black, graphite, oatmeal and white.

Other minerals found here are graphite, alum, potter's clay and roofing-slate, and, besides, famous silvermines were worked at Iglau during the middle ages.

A few other minerals may be noticed, and some have been worked to a small extent - graphite is abundant, particularly near Upernivik; cryolite is found almost exclusively at Ivigtut; copper has been observed at several places, but only in nodules and laminae of limited extent; and coal of poor quality is found in the districts about Disco Bay and Umanak Fjord.

Calcium carbide, graphite, phosphorus and carborundum are now extensively manufactured by the operations outlined above.

This dissolves out the zinc. Lime is added to bring down the gold, and the sediment, after washing and drying, is fused in graphite crucibles.

The densest anthracite is of ten of a semi-metallic lustre, resembling somewhat that of graphite.

Formerly bullion was melted in crucibles made of refractory clay, but they are liable to crack and require careful handling These were succeeded by iron crucibles, especially for melting silver, and these have now been generally replaced by graphite (plumbago) crucibles made of a mixture of clay and graphite.

Good graphite crucibles can be used many times in succession if they are heated gradually each time, but they are usually discarded after about fifteen or twenty meltings.

In its output of graphite Czechoslovakia takes second place among European countries, Great Britain being the first.

The graphite found in granite and in veins in gneiss, as well as that contained in meteoric irons, cannot have had such an origin.

Iodine is a greyish-black shining solid, possessing a metallic lustre and having somewhat the appearance of graphite.

The meta-sedimentary rocks of the Archean include metamorphosed limestone, and schists which carry carbonaceous matter in the form of graphite.

The marble and graphite, as well as some other indirect evidence of life less susceptible of brief statement, have been thought by many geologists sufficient to warrant the inference that life existed before the close of the era when the Archean rocks were formed.

Deposits of crystalline graphite are found in Chester and Berks counties.

It was also necessary to give the fine charcoal a thin coating of calcium oxide by soaking it in lime-water, for the temperature was so high that unless it was thus protected it was gradually converted into graphite, losing its insulating power and diffusing the current through the lining and walls of the furnace.

The chief mineral deposits in Bavaria are coal, iron ore, graphite and salt.

If, ignoring temporarily and for simplicity the fact that part of the carbon may exist in the state of graphite, we consider the behaviour of iron in cooling from the molten state, AB and BC give the temperature at which, for any given percentage of carbon, solidification begins, and Aa, aB, and Bc that at which it ends.

We may mention also graphiticschists containing dark scaly graphite (often altered forms of carbonaceous shales), and haematite-schists which may represent beds of ironstone.

Mining is only of slight importance, small quantities of coal and iron-ore being extracted in the Alpine foothill region; graphite is found near Miihldorf.

Graphite is widely distributed in the Adirondack region, but the mining of it is confined for the most part to Essex and Warren counties; in 1908 the output was 1,932,000 lb.

Other minerals which occur in the rocks of this group are calcite, garnet, biotite, chloritoid, epidote, tourmaline and graphite or dark carbonaceous materials.

The graphite of New York, Pennsylvania and Alabama is "flake" and unsuitable for this purpose.

Of great importance is the chemical identity of the diamond, graphite and charcoal, a fact demonstrated in part by Lavoisier in 1773, Smithson Tennant in 1796, and by Sir George Steuart-Mackenzie (1780-1848), who showed that equal weights.

The crucible is at a red heat when the gold is charged in, the copper being added last, and a graphite lid put on the crucible to check loss by volatilization.

The graphite veins in the older crystalline rocks are probably akin to metalliferous veins and the material derived from deep-seated sources; the decomposition of metallic carbides by water and the reduction of hydrocarbon vapours have been suggested as possible modes of origin.

Acheson, in 1896, patented an application of his, carborundum process to graphite manufacture, and in 1899 the International Acheson Graphite Co.

The precipitated gold is washed, treated with salt and sulphuric acid to remove iron salts, roughly dried by pressing in cloths or on filter paper, and then melted with salt, borax and nitre in graphite crucibles.

Klaproth in 1799, is obtained when pure carbon (graphite or charcoal) is oxidized by alkaline permanganate, or when carbon forms the positive pole in an electrolytic cell (Ber., 1883, 16, p. 1209).

Beds of excellent graphite have been found in the Kitoi Alps (Mount Alibert) and in the Turukhansk district in.

Near Tiverton and Cranston graphite has been quarried.

Graphite has been discovered in the P.O.

Gold, coal, iron, graphite, copper and salt have been found.

It is found native as the diamond (q.v.), graphite, as a constituent of all animal and vegetable tissues and of coal and petroleum.

They are rarely metamorphosed to the point of recrystallization, though locally shales are altered to roofing slates, sandstones are indurated, limestones slightly marblized, and coals, originally bituminous, are changed to anthracite in northern Pennsylvania, and to graphite in Rhode Island.

The yield of iron ore is almost one million tons annually, while gold, silver, tin, graphite and salt are also mined.

Henri Moissan obtained the metal of 99% purity by electrolysing calcium iodide at a low red heat, using a nickel cathode and a graphite anode; he also showed that a more convenient process consisted in heating the iodide with an excess of sodium, forming an amalgam of the product, and removing the sodium by means of absolute alcohol (which has but little action on calcium), and the mercury by distillation.

The solution of metallic chlorides or sulphates so obtained is precipitated by iron, the metallic bismuth filtered, washed with water, pressed in canvas bags, and finally fused in graphite crucibles, the surface being protected by a layer of charcoal.