Carbon rod

“ A thin carbon pencil, forming a bridge between two stout carbon rods, is set in the midst of the mixture to be heated. On passing a current through the carbon the small rod is heated to incandescence, and imparts heat to the surrounding mass. On a larger scale several pencils are used to make the connexions between carbon blocks which form the end walls of the furnace, while the side walls are of fire-brick laid upon one another without mortar. ”

“ When the carbon rods are brought into contact and then slightly separated, a spark passes between them. Particles of carbon are torn off by the spark and volatilized, and these incandescent particles form a sort of bridge which is a sufficiently good conductor for the current to pass across it from one rod to the other. When the carbons are placed horizontally, the glowing mass is carried upwards by the ascending currents of heated air, and it assumes the arch-like form from which it gets its name. ”

“ In the Bernardos and Olszewski process the work is made the negative pole of a direct current circuit, and an arc is drawn between this and a carbon rod, to which a handle is attached for manipulating. As this rod is the positive terminal, particles of carbon may be introduced as a constituent of the metal taking part in the operation, making it hard and brittle, and causing cracks in the joint or filling; the metal may, in fact, become very hard and unworkable. ”

“ Then the strength of the shunt current diminishes considerably, and the solenoid, S, recovers briskly its drawing power upon the rod, and contact is restored. The carbons approach during these periods only about 0.01 to 0.02 millimeter. If this is not sufficient to restore equilibrium it is repeated continually, until equilibrium is obtained. The result is that the carbon is continually falling by a motion invisible to the eye, but sufficient to provide for the consumption of the carbons. ”

“ A short distance below the carbon are the two terminals of the electric circuit which, when completed by the lowering of the carbon, gives the alarm. Now if there be a very gradual change of temperature the steel rod lengthens slowly, and so does the copper wire, so that the amount of sag remains practically what it was before. But in event of a fire the copper expands much more quickly than the steel, and sags until the carbon completes the circuit. ”

“ Carbon possesses a natural power to prevent a limited amount of polarization by absorbing the hydrogen gas coming from the zinc rod; hence it is used in various shapes for open circuit cells, which gives rise to as many different names, such as Samson, Hercules, Law, National, Standard, etc. In all these types of cell, sal-ammoniac and zinc are used, and by corrugating the carbon, fluting it, or making concentric cylinders, special merits are obtained in each case. ”

“ It is made use of in Sweden, and has been demonstrated in the United States, to determine the quantity of carbon in steel. An intelligent blacksmith is given a set of rods of predetermined carbon, ranging from 100 carbon to zero, or through any range that may be necessary; each rod is marked to indicate its carbon. He takes the rods one by one and heats them until they scintillate, well up into the granular condition, then lays them on his anvil and hammers them, observing carefully the color at which each one becomes plastic as it cools slowly. ”

“ The subsequent raising of the core therefore turns the wheels, raises the rack rod, and strikes the arc. The feed is operated by the weakening of the magnetic field of the coil, which causes the core to lose its grip of the wheels, and allows the top carbon to descend. The catch, L, Fig. 8, has a lateral play, and serves to engage in the teeth of the rack rod, so as to prevent its falling when being trimmed. Each carbon when in position is held against two rectangular guide bars by the pressure of a wire spring—see figure. ”

“ The experiments made to test this alleged “property” of carbon are absolutely conclusive. The author of this book has shown [39] that when a rod of dense artificial coke-carbon, such as is used in many forms of telephone transmitters, such as Crossley’s for example, is subjected to pressure varying from less than one dyne per square centimetre up to twenty-three million times that amount, the resistance of the rod did not decrease by so much as one per cent. ”

“ Only very light pressure should be used on the drill. The carbon is fastened to a strip of wood, about an inch and one-quarter wide, one-half an inch thick, and a little longer than the top of the glass jar is wide.
Fig. 60.—A Method of making a Cell Element from Carbon Rods. A piece of heavy sheet zinc is fastened on the other side opposite the carbon, with a screw. It is a good idea to paint the screws and the surrounding portions of both the zinc and the carbon with hot paraffin wax so that the solution will not "creep" and attack the screws. ”

“ A brass chip fastened to the wood keeps the thin rod of carbon in position, and when two copper wires connect the carbons with six to ten jars of a bichromate battery, a light appears where the two carbons meet. As the thin rod wastes away, the cork rises and keeps the end of the rod almost in contact with the other carbon point.
An ambition to creditably make a mechanical contrivance or apparatus is noticeably characteristic of many boys. The construction of an aquarium, a sailboat, or a telescope, or some similar object, is of absorbing interest to such lads ”

“ While it is true that carbon in the form of charcoal burns so readily that it is used instead of kindlings for lighting a fire, carbon in the form of graphite in our so-called "lead" pencils and carbon as it is prepared for electric light pencils burns only very slowly even at exceedingly high temperatures. The carbon rods used in arc lamps endure a temperature of over 6000 degrees, without losing more than one inch an hour, and half of that is simply volatilized—not burned. ”

“ The simplest method is to place a carbon plate on each side of the wooden strip and use a zinc in the form of a rod which passes through a hole between the two. Care must always be used to keep any screws which are used to hold the carbons or zincs in position in the cells from touching each other. ”

“ Thousands of feet of carbon rods are volatilized every night in the arc lamps of our cities, but the trouble is that this carbon vapor so formed, when cooled, or condensed, is not converted into the exceedingly hard, clear, crystalline diamond, but into the soft, dull black graphite or plumbago. ”

“ If the iron core be attached to one end of a lever, the other end of which carries the upper carbon, it will be seen that if the carbons are in contact and the current is switched on, the series coil alone will be traversed by the current, and its magnetic action will draw down the iron core, and therefore pull the carbons apart and strike the arc. The moment the carbons separate, there will be a difference of potential between them, and the shunt coil will then come into action, and will act on the core so as to draw the carbons together. ”

“ This gas, previously purified, circulates around the platinum filament, through which an electric current is passed sufficient to bring it to a red heat. This decomposes the gas, and a thin coating of absolutely pure carbon is deposited on the wire. The operation is continued until a sufficient thickness of carbon has been deposited for each type of lamp, and the method of regulating the amount of deposit is effected very simply, and, in fact, almost automatically. ”

“ Oxygen and nitrogen are free as air, and as we have seen in the second chapter, their direct combination by the electric spark is possible. Hydrogen is free in the form of water but expensive to extricate by means of the electric current. But we need more carbon than anything else and where shall we get that? Bits of crystallized carbon can be picked up in South Africa and elsewhere, but those who can afford to buy them prefer to wear them rather than use them in making synthetic food. Graphite is rare and hard to melt. We must then have recourse to the compounds of carbon. ”

“ In other words, the steam furnishes both heat and oxygen for the instant conversion of the coal-dust to carbonic acid, with the consequent release of its own prodigious volume of hydrogen. Under their own increased pressure, the gases continue without pausing, down though the mass of glowing coals. In making this passage, the carbonic acid takes up a double portion of carbon from the hot coals and becomes carbonic oxide—the powerful heating gas so often seen burning in a lambent violet flame on the surface of anthracite fires when the air is let in on them. ”

“ Another way is to make the steel by the converter plan, wherein fused cast iron is decarbonised, by the blowing in of air, which burns off the carbon, leaving the contents of the vessel in the state of fluid wrought iron, and then to run in so much of a metal rich in carbon as shall give to the whole charge, the proportion required. The third mode, the open hearth, consists in melting the material in gas furnaces, and so proportioning the mixture, as to obtain the desired amount of carbonisation, ascertaining before tapping, what the condition really is, by means of test pieces. ”

“ These latter are provided beneath with small glass rods, G, G, whose extremities toward the arc abut at a short distance from the latter against a nickel stop, L (Fig. 3) , which supports them, moreover, at M, by means of a tappet whose position is regulated by a screw. The current is transmitted to the carbons by two friction rollers, I, I, which serve at the same time as a guide for them, and which give the electric flux a passage of only one or two centimeters over the front of the carbon to form the arc. ”

“ If the carbon arresters are separated by celluloid, it will burn away and allow the carbons to come together, extinguishing the arc. If they are separated by mica and one of the carbons is equipped with a globule of low-melting alloy, the heat of the arc will melt this, short-circuiting the gap and extinguishing the arc. The passage of current to ground at the arrester, however, will be over a path containing nothing but wire and the arrester. ”

“ The crucibles are then heated to a high temperature in an ordinary combustion or electric furnace, whereby the organic matter is destroyed, and a skeleton of carbon remains. The higher the temperature at which this carbonization is conducted, the denser is the resulting product. The filaments so prepared are sorted and measured, and short leading-in wires of platinum are attached to their ends by a carbon cement or by a carbon depositing process, carried out by heating electrically the junction of the carbon and platinum under the surface of a hydrocarbon liquid. ”

“ On the other hand, carbonic acid gas passing over red-hot coals takes up from them the additional proportion of carbon, and is, we may say, unburnt into carbonic oxide. When we see a pale blue flame flickering over the bright embers in a fire grate, it is carbonic oxide burning back again by taking more oxygen from the air above the coals. Carbonic oxide combines directly with two or three of the metals, as, for instance, it forms a volatile compound with nickel, at a certain temperature, and this is decomposed again at a higher temperature. ”

“ In order to reduce their resistance a soft-metal inner core is used. The carbons, instead of being placed one above the other, are inclined at a small angle with the arc between their lower ends. The arc is made as large as possible by the action of a small electromagnet placed just above the gap.
The feeding mechanism is similar in principle to that used for ordinary carbon arcs. For street lighting, lamps of the magazine type are used. In these lamps a number of pairs of carbons is placed in the magazine, and as each carbon is used up, a new one automatically takes its place. ”

“ Those to the left of the eutectic or exact 4.3% composition do so by the gradual freezing out of iron containing the maximum or 1.7% of carbon, i.e., iron is taken out faster than carbon, hence there is gradual concentration of carbon in the remaining liquid. This goes on until 4.3% is reached. The compositions to the right of the line WX throw out the chemical compound, Fe3C, which contains 6.6% of carbon, whereby carbon is eliminated faster than iron and the desired 4.3% carbon alloy is arrived at from the other direction. ”

“ The very ore, the coal, the presence of oxygen, the excess of it, all vary the quality of the material. An excess of carbon is more detrimental than a scarcity; for where carbon has once been, it leaves an indelible mark, and though extracted to as great an extent as practicable, it leaves a residue that possesses an affinity to absorb carbon again equal to the original quantity: thus, steel once made will never, by any process yet known, be reconverted back to iron of the same nature it was originally. ”

“ In the course of manufacture a process is generally applied to the carbon which is technically termed “treating.” The carbon filament is placed in a vessel surrounded by an atmosphere of hydrocarbon, such as coal gas or vapour of benzol. If current is then passed through the filament the hydrocarbon vapour is decomposed, and carbon is thrown down upon the filament in the form of a lustrous and dense deposit having an appearance like steel when seen under the microscope. ”