1

gravity of about 3.52. The diamond is the hardest known substance, and is hard even after being reduced to the finest practicable powder. Graphite is the softest substance dug from the earth. Although it will neither melt nor consume, graphite will gradually waste if kept on a very hot fire; but a piece having sharp, projecting angles, has been subjected for two hours to a heat which would melt steel without disturbing the sharpest points. This quality of refractori ness gives it its value for crucibles; and as the cables of the suspension-bridge connecting New York and Brooklyn are to be constructed of the steel known as "crucible" steel, and that can be produced only by using crucibles made by the Dixon process, it is quite cor

SPECIMEN OF EARLY HIERATIC WRITING.

combustion being hindered rather than helped, so far as known, by the slate and other materials which remain as refuse after burning. The diamond is regarded as perfectly pure carbon, and by subjecting it to a very intensified heat it undergoes some change which leaves it a cinder-like mass; but science can neither reverse the process nor produce the diamond artificially. Anthracite coal has a specific gravity of 1.36 to 1.85,-nearly the same as graphite, but the diamond, in substance almost identical with graphite, is considerably heavier, having a

A CRUCIBLE.

rect to represent the graphite crucible as the mold through which the supports of the bridge must pass to completion.

The soft graphite of which the carvings illustrated were cut-softer than any pencil to the knife and a common substance-is, by analysis, the same thing, excepting a mere trace of impurity, as the rare, costly, and hard diamond, which is nearly twice as heavy. The graphite crucible or pot, buried to the top in a mass of burning anthracite. -carbon in carbon,-refuses to burn itself

The use of metallic lead for marking is very old. Pliny refers to it for marking lines on papyrus. La Moine cites a document 1387 ruled with graphite; Cortez found the Aztecs, in 1520, using crayons of it, probably obtained from the Sonora mine. But the most famous mine was that of Borrowdale, in Cumberland, England, discovered in 1564. The quantities obtained were of small size, in "pockets." The new material was so highly desired, and was so closely maintained as a monopoly, that, in pursuance of an act of Parliament, the mouth of the mine was guarded by an armed force, but unlawful access was obtained by burrowing secret passages underground. To keep up the monopoly, the mine was worked only six weeks in the year, and its mouth was closed by flooding with water when the workmen retired, the product of that short time being sometimes worth $200,000 in market. The process of preparing the graphite for use was the simple one of dividing it into slips. A plan is also recorded -although it could hardly have been used to any practical purpose-by which sawed

pulverized graphite, by hydraulic presses, into solid blocks, which were afterward sawed into bars and inserted in the wood. This description only is given by several of the best approved cyclopedias, of recent editions; but for pencil-making on any considerable scale, it is impracticable.

Possessing smoothness without stickiness, graphite is indispensable for dry lubrication, as in the action-work of the piano and the slides of the pipe-organ. For lubrication of wooden surfaces in machinery, for polishing shot and the like, and for a variety of purposes in the trades, it has great value. American graphite, being of two distinct formations, is adapted for both crucibles and pencils; that of Ceylon, being of a single formation or kind, is suitable for crucibles only. The process of crucible-making is very simple. The graphite, reduced to a powder just coarse enough to leave its natural glistening appearance, is mixed with water to the proper consistency, a peculiar clay brought down the Rhine from Mayence being added, to give it cohesion, with a little fine charcoal to give it porousness.

The plastic mass is then pressed upon a small horizontal wheel, and the workman

as to the way of turning his wheel, the potter of to-day works as the oldest potters worked of whom we have historic knowledge.

The only graphite mine of consequence in this country is at Ticonderoga, N. Y., owned and worked by the Dixon Crucible Company of Jersey City, whose distinctive processes of manufacture are referred to throughout in this article. The mine closely resembles an anthracite coal mine in external and internal appearance, some of the workings being 300 feet below the surface, ventilated by air-shafts, or by mechanical appliances. The graphite runs in nearly vertical veins, inclosed in hard gneiss rock, which is first removed by blasting on each side of the vein, leaving that standing, inclosed in its rock wall, somewhat like a partition in a house; the wall is then broken up and the lumps of graphite, separated as nearly as possible from the rock. are lifted to the surface, only so much of the rock itself being taken out as is necessary to keep the working-space clear. The large veins are of the "foliated" or crystal

same

molds it into the shape of a jar by his hands, as it revolves, adding a "lip' or mouth out of which to pour its contents. The crucible is the ancient pot, scarcely changed; the wheel and the process of shaping are the as were employed in the days of Moses. Formerly the wheel was turned by hand, the workman taking it by the edge and giving it a spin, then applying both hands to the shaping until the velocity was exhausted and a new start became necessary. This was called a "throw "-wheel, and the first improvement was in placing an additional wheel underneath on the same spindle, so that the workman could keep up the motion by pushing the edge of the lower one with his foot; this was called

a

"kick"-wheel. The next step was to add levers, to be worked more conveniently by the foot, and the wheel was called a "tread". wheel, leaving no other improvement to be made but the addition of power. Except

LARGEST PIECE OF NATIVE GRAPHITE EVER SHIPPED FROM CEYLON, WITH CINGALESE INSCRIPTION. WEIGHT, 237 LBS.

ELEPHANT CARVED FROM A LUMP OF CEYLON GRAPHITE, BY A NATIVE WORKMAN IN THE MINES.

lized formation, used only for crucibles, the compact or granulated form of deposit. which alone is available for pencil-making. being in small veins and what miners call "pockets." The two formations lie together. but are not united closely, and an interesting example is shown in the specimen of which an illustration is given. This specimen was accidentally dropped in handling, after being kept a long time, and it separated between the two formations on a line as clean and sharp as if cut by a tool.

The graphite is taken, "in the lump." direct from the mouth of the mine to the reducing mill; here it is pulverized by "stamps," under water, the particles floating off with the water through a series of tanks. It comes to the factory in Jersey City in barrels, in the form of dust. If intended for crucibles, it is in scales, very fine but glistening, resembling the choicest gunpowder, but flatter. If for pencils, the proc

DIAGRAM OF GRAPHITE MINE.

ess of pulverizing has been continued until the graphite is an impalpable powder, lusterless, and of a dingy color. It is then finer and softer than any flour, but does not cohere like flour; it can be taken up in the hand, just as water can, and is hardly retained more easily than water is; if one attempts to take a pinch of it between forefinger and thumb it is as evasive as quicksilver, and the only sensation is that the flesh is smoother than before; although it crocks the skin, to the sense of touch it is literally only a polish.

Its extraordinary purity should be noted. At the Ticonderoga mills, it is refined, for the choicest uses, until it is 99.96 per cent. carbon, leaving less than one-twentieth of one per cent. of other matter-merely a trace. In 100 pounds there is therefore about two-thirds of an ounce of foreign substance, or about one pound in a ton. No other mineral has been found in its natural state so pure. California gold averages about 875 to 885 fine, with some equal to the standard of coin, which is 900; Australian gold averages 960 to 966 parts in the 1,000; the purest specimen ever found was probably one from the Ural Mountains, which was 98.96 per cent. fine. This finest specimen had 1.04 per cent. of foreign substance, against 0.20 per cent. in the purest graphite; or, stating it in another way, the finest gold known had more than five times, and the average gold produced has twenty to fifty times, as much impurity as the finest Ticonderoga graphite. And so far as our present knowledge goes, this mere trace of impurity is all which makes the graphite different in substance from the diamond!

The first process in lead-making is to separate the graphite dust further according to fineness. It is mixed with sufficient water to run very freely, and is then turned into a hopper, from which the water runs slowly

through a series of tubs, as shown in the illustration. The coarsest and heaviest particles settle to the bottom of the first tub, the next coarsest and heaviest in the next, and so on, the movement of the water being made very gentle; on reaching the last tub, the powder, being twice as heavy as water and sinking in it if undisturbed, has so far settled that the water discharges at the top nearly clear. After the flow is stopped and the powder has been allowed to settle, the clear water is withdrawn by removing successively, beginning with the upper one, a number of plugs inserted in holes in the side of each tub, care being used not to agitate the contents so as to disturb the deposited dust; this being done properly, the deposit is removed through the gates at the bottom of each tub. The separation is thus

performed, by this ingenious process of "floating," more perfectly than it could be by any direct handling, dry treatment being wholly impracticable. For the finest pencils, the deposit from the last tub only is used, but for ordinary and cheap grades that from the two before the last will answer.

The graphite is now ready for the clay. This is a peculiar pipe-clay from Germany; after being subjected to the "floating" process, the finest is mixed with the graphite, in proportions varying according to the degree of " hardness" required. The more clay used, the "harder" the pencil; for medium grades the proportion is about seven parts clay to ten graphite, by weight.

STRAIGHTENING THE LEADS.

The graphite and clay are mixed together with water, to the consistency of thick cream, and the mixture is fed to the grinding mills, which consist of two flat stones about two feet in diameter, placed horizontally, only the upper one running. Between these the mass is ground like paint,-for the finest pencils as many as twenty-four times, thus securing the most perfect strength, uniformity and freeness from grit in the leads. After grinding, the mass is inclosed in stout canvas bags, and the clear water forced out by hydraulic pressure, until it becomes a thick dough; it then goes to the forming-press. This is simply a small vertical iron cylinder, having a solid plunger or piston, driven by a screw. plate is inserted in the bottom, having an opening of the shape and size of the lead desired, and the graphite is slowly forced through the hole, exactly as stream of water is forced from a syringe, coiling

A

a

itself round and round like a coil of wire on a board set beneath the press. The coil is taken up at intervals, "rove" off straight by the hands into lengths sufficient for three leads, which are straightened out, laid in order on a board, pressed flat by putting a cover over them, and are finally hardened by placing them in a crucible and baking in a kiln. The handling must be done expeditiously, as the leads begin drying immediately and become brittle as they dry; but on first issuing from the press they are so plastic that knots may be tied loosely in them. A coil 4,000 feet long, in an unbroken piece, was exhibited by the Dixon Company at Philadelphia; it was run as a curiosity, the length being determined by weighing a small portion; but there would be no practical difficulty in making a coil long enough for an ocean cable or for Puck's promised girdle around the earth.

The leads are now ready for their wooden case. For the cheapest pencil pine is used; for the common grades, an ordinary quality of red cedar; for all the standard grades, the Florida Keys cedar, which is soft and close-grained, and is so superior for the purpose that even the European pencilmakers are obliged to come to Florida for it. At the saw-mills in Tampa, Florida, the cedar is cut into blocks about seven inches long, and these are sawed into strips about 31⁄2 inches wide and three-sixteenths of an inch thick. The pencil consisting of two parts glued together, with the lead between, each strip is wide enough to make the halves of six pencils; the pencils are made six at a time, and imperfect strips

BAKING THE LEADS.