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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 rect to represent the graphite crucible as the other materials which remain as refuse after mold through which the supports of the burning. The diamond is regarded as per- bridge must pass to completion. fectly pure carbon, and by subjecting it to a The soft graphite of which the carvings very intensified heat it undergoes some illustrated were cut—softer than any pencil change which leaves it a cinder-like mass; to the knife and a common substance—is, but science can neither reverse the process by analysis, the same thing, excepting a nor produce the diamond artificially. Anthra- mere trace of impurity, as the rare, costly, cite coal has a specific gravity of 1.36 to and hard diarnond, which is nearly twice as 1.85,-nearly the same as graphite,—but the heavy. The graphite crucible or pot, buried diamond, in substance almost identical with to the top in a mass of burning anthracite. graphite, is considerably heavier, having a carbon in carbon,—refuses to burn itself and melts its metallic contents. The carbon slices were brought to roundness by being diamond is hard; the carbon graphite is drawn through holes in rubies, the first hole soft; the carbon anthracite burns; the car- being eight-sided, the second sixteen-sided, bon graphite will not burn. Why these and the third round. Rushes for chairs, things are so is a part of the mysterious and sometimes other materials, are reduced chemistry of nature which has thus far baf- in size by this “ drawing” process; but it fled every experiment of analysis and every could not well be used with graphite. A hypothesis of science.
very old process consisted of compressing
The use of metallic lead for marking is pulverized graphite, by hydraulic presses,
Pliny refers to it for marking lines into solid blocks, which were afterward on papyrus. La Moine cites a document sawed into bars and inserted in the wood. of 1387 ruled with graphite; Cortez found This description only is given by several of the Aztecs, in 1520, using crayons of it, the best approved cyclopedias, of recent probably obtained from the Sonora mine. editions ; but for pencil-making on any But the most famous mine was that of considerable scale, it is impracticable. Borrowdale, in Cumberland, England, dis- Possessing smoothness without stickiness, covered in 1564. The quantities obtained graphite is indispensable for dry lubrication, were of small size, in “pockets.” The new as in the action-work of the piano and the material was so highly desired, and was so
slides of the pipe-organ. For lubrication closely maintained as a monopoly, that, in of wooden surfaces in machinery, for polishpursuance of an act of Parliament, the ing shot and the like, and for a variety mouth of the mine was guarded by an of purposes in the trades, it has great value. armed force, but unlawful access was ob- American graphite, being of two distinct tained by burrowing secret passages under- formations, is adapted for both crucibles and ground. To keep up the monopoly, the pencils; that of Ceylon, being of a single mine was worked only six weeks in the year, formation or kind, is suitable for crucibles and its mouth was closed by flooding with only. The process of crucible-making is water when the workmen retired, the product very simple. The graphite, reduced to a of that short time being sometimes worth powder just coarse enough to leave its $200,000 in market. The process of preparing natural glistening appearance, is mixed with the graphite for use was the simple one of water to the proper consistency, a peculiar dividing it into slips. A plan is also recorded clay brought down the Rhine from May-although it could hardly have been used ence being added, to give it cohesion, with to any practical purpose-by which sawed a little fine charcoal to give it porousness. The plastic mass is then pressed upon a as to the way of turning his wheel, the potsmall horizontal wheel, and the workman ter 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 LUMP OF NATIVE TICONDEROGA GRAPHITE, SHOWING THE TWO FORMATIONS.
rock, which is first removed by blastmolds it into the shape of a jar by his hands, ing on each side of the vein, leaving tha: as it revolves, adding a "lip” or mouth standing, inclosed in its rock wall, somewhat out of which to pour its contents. The cru- like a partition in a house; the wall is ther. cible is the ancient pot, scarcely changed; broken up and the lumps of graphite, sepathe wheel and the process of shaping are the rated as nearly as possible from the rock, same as were employed in the days of are lifted to the surface, only so much of Moses. Formerly the wheel was turned by the rock itself being taken out as is neceshand, the workman taking it by the edge sary to keep the working-space clear. The and giving it a spin, then applying both large veins are of the “ foliated” or crystalhands 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
ELEPHANT CARVED FROM A LUMP OF CEYLON GRAPHITE, a “kick"-wheel. The next step was to add levers, to be worked more conveniently by lized formation, used only for crucibles, the the foot, and the wheel was called a “ tread”- compact or granulated form of deposit. wheel, leaving no other improvement to be which alone is available for pencil-making. made but the addition of power. Except 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 මගෙ රට
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.
BY A NATIVE WORKMAN IN THE MINES
LARGEST PIECE OF NATIVE GRAPHITE EVER SHIPPED FROM
DIAGRAM OF GRAPHITE MINE.
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 is 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 ess of pulverizing has been continued until the contents so as to disturb the deposited the graphite is an impalpable powder, lus- dust; this being done properly, the deposit terless, and of a dingy color. It is then finer is removed through the gates at the botand softer than any flour, but does not tom of each tub. The separation is thus 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 performed, by this ingenious process of one per cent of other matter—merely a "floating," more perfectly than it could be trace. In 100 pounds there is therefore by any direct handling, dry treatment being about two-thirds of an ounce of foreign sub- wholly impracticable. For the finest pencils, stance, or about one pound in a ton. No the deposit from the last tub only is used, other mineral has been found in its natural but for ordinary and cheap grades that state so pure. California gold averages
from the two before the last will answer. about 875 to 885 fine, with some equal to the The graphite is now ready for the clay. standard of coin, which is goo; Australian This is a peculiar pipe-clay from Germany; gold averages 960 to 966 parts in the 1,000; after being subjected to the "floating" procthe purest specimen ever found was proba- ess, the finest is mixed with the graphite, bly one from the Ural Mountains, which in proportions varying according to the was 98.96 per cent. fine. This finest spec
This finest spec- degree of " hardness" required. The more imen had 1.04 per cent. of foreign sub- clay used, the “harder” the pencil; for stance, against 0.20 per cent in the purest medium grades the proportion is about graphite; or, stating it in another way, the seven parts clay to ten graphite, by weight. 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
LUMP OF CLAY, WITH GOVERN.
BUNCH OF LEADS, IN
GRAPHITE THROUGH THE TUBS.
STRAIGHTENING THE LEADS.
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 pencilThe graphite and clay are mixed together makers are obliged to come to Florida for with water, to the consistency of thick it. At the saw-mills in Tampa, Florida, cream, and the mixture is fed to the grind- the cedar is cut into blocks about seven ing mills, which consist of two flat stones inches long, and these are sawed into strips about two feet in diameter, placed horizon- about 372 inches wide and three-sixteenths tally, only the upper one running. Between of an inch thick. The pencil consisting of these thé mass is ground like paint,-for two parts glued together, with the lead the finest pencils as many as twenty-four between, each strip is wide enough to make times, thus securing the most perfect the halves of six pencils; the pencils are strength, uniformity and freeness from grit made six at a time, and imperfect strips 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. A 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 a stream of water is forced from a syringe, coiling
BAKING THE LEADS.