Carbon electrode

“ No old cell can be made as good as new by any method. Never drop the cells on the floor nor subject them to hard usage mechanically, for if the active material is loosened, the current output will be reduced. A short circuit through a closed switch with the engine stopped or a loose dangling wire will put the cells beyond repair.
If the binding screw on the carbon electrode does not make good contact with the carbon, tighten it to decrease the resistance. ”

“ Furnace electrodes frequently consist of carbon rods, and if there is a short gap between them, forming a break in the circuit, the current jumps across that gap, forming an "arc." The intense heat of the arc is used in fusing and melting metals. As large electrodes are necessary for use in furnaces where great masses of metal are melted, so small electrodes are adapted to finer or more delicate work, says Popular Electricity.
Pencil Electrodes Which Furnish Intense Heat
As the lead or graphite in a lead pencil is a form of carbon, it will make an excellent electrode for small work. ”

“ For carbon electrodes in air at atmospheric pressure m is about 39 volts, varying somewhat with the size and purity of the carbons; it is diminished by soaking the terminals in salt solution. The value of n given by different observers varies considerably, ranging from .76 to 2 volts when l is measured in millimetres; it depends upon the current, diminishing as the current increases. When metallic terminals are used instead of carbons, the value of m depends upon the nature of the metal, m in general being larger the higher the temperature at which the metal volatilizes. ”

“ This arrangement offers another advantage, namely, that the length of that portion of the carbon rods which is conveying the current is always the same notwithstanding the shortening of their total length by combustion; the resistance of the carbon electrodes is, therefore, maintained constant, and, for the reason that the contact piece presses against the rods very near their lower ends, that resistance is reduced to a minimum. In this way very long carbons, such, for instance, as will burn for ten or sixteen hours, can be used without introducing any increase of resistance into the circuit. ”

“ Early in the history of electric lighting it became apparent that the proper construction of the carbon electrodes was a highly important item in the manufacture of a lighting apparatus. The value of carbons depends largely upon their purity and freedom from ash in burning, and it required a countless number of experiments to develop the highly efficient carbons now in general use. Davy made use of pieces of wood charcoal in his experiments, but these were too fragile to be of practical value, even if their other qualities had been ideal. ”

“ This charcoal filament has so much greater resistance than the wires that it opposes, or resists, the passage of the electricity through it; but the electricity must go through, and, as it is strong enough to force its way, it overcomes this resistance and passes on through the carbon to the wire at the other end. You see it is a struggle between the carbon and the electricity, the current being determined to go on and the carbon trying to keep it back; and, in the end, the electricity, being the stronger, gets the best of it ”

“ Alumina and lime, for example, which cannot be reduced at ordinary furnace temperatures, readily give up their oxygen to carbon in the electric furnace, and then combine with an excess of carbon to form metallic carbides. In 1885 the brothers Cowles patented a process for the electrothermal reduction of oxidized ores by exposure to an intense current of electricity when admixed with carbon in a retort. ”

“ 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. ”

“ In order to ensure a large surface of contact for the terminal of the carbon rod or plate, it is customary to cast a leaden cap on the top thereof; and, as the porosity [Pg 35] of the graphite, or carbon, is very apt to allow the fluid in the battery to creep up to and corrode the terminal, and thus oppose resistance to the passage of electricity, the upper end of the carbon, before the lead cap is cast on, is soaked for some time in melted paraffin wax, at a temperature of 110° Centigrade: that is somewhat hotter than boiling water heat. ”

“ If some source of continuous electric current is connected to rods of such carbon, first brought into contact and then slightly separated, the following facts may be noticed: With a low electromotive force of about 50 or 60 volts no discharge takes place until the carbons are in actual contact, unless the insulation of the air is broken down by the passage of a small electric spark. When this occurs, the space between the carbons is filled at once with a flame or luminous vapour, and the carbons themselves become highly incandescent at their extremities. ”

“ If, however, we now connect the two plates together by means of any conductor, say a copper wire, then the strain to which the carbon plate is subjected finds its exit along the wire and the zinc plate, which is continually losing its strain under the influence of the acid, being thus at a lower potential (electrical level, strain) than the carbon, can and does actually take in and pass on the electric vibrations. It is therefore evident that no true "current" can pass unless the two elements of a battery are connected up by a conductor. ”

“ After the plug has been inserted and the joint properly luted, the electric circuit is closed and the current allowed to pass through the retort, traversing its entire length through the body of mixed ore and carbon. The carbon constituents of the mass become incandescent, generating a very high degree of heat, and being in direct contact with the ore, the latter is rapidly and effectually reduced and distilled. ”

“ Why may not the union of carbon with oxygen be made to generate electric currents instead of heat? Electric energies have been made that convert into mechanical effect 60 to 70 per cent, of the energy of the electric current, and a much higher efficiency might, no doubt, be obtained. Already something has been done toward the generation of electric currents by the union of carbon and oxygen; but, so far, no means has been discovered by which such a union can be effected, except at a high temperature, and this involves a great waste of energy in the form of heat. ”

“ Take a glass tube filled with oxygen gas, and put in it a lump of charcoal, cork the ends of the tube tightly, and pass through the corks the wires of an electrical battery. By passing a stream of electrical fluid over the charcoal it may be ignited, when it will burn with great brilliancy. In burning it is dissolved in the oxygen forming carbonic acid, and disappears. It is no more lost, however, than is the carbon of wood which is burned in a stove ”

“ It is now easy to understand how the system operates; when the current is not traversing the circuit, the carbons are separated; but, at the moment the circuit is closed for lighting a series of lamps, it traverses the electro-magnet, which then becomes very powerful, and draws down the cores, F, along with the lever, L, the tube, TT', and the carbon-holder, CC', and brings the carbons in contact. ”

“ Experiments already made so that aluminum, silicon, boron, manganese, magnesium, sodium and potassium can be reduced from their oxides with ease. In fact, there is no oxide that can withstand temperatures attainable in this electrical furnace. Charcoal is changed to graphite. Does this indicate fusion or solution of carbon? As to what can be accomplished by converting enormous electrical energy into heat within a limited space, it can only be said that it opens the way into an extensive field for both pure and applied chemistry. ”

“ In such a furnace a continuous current, for example, of 3000 amperes, at 50 to 60 volts, may be used at first, increasing to 5000 amperes in about half an hour. The reduction is not due to electrolysis, but to the action of carbon on alumina, a part of the carbon in the charge being consumed and evolved as carbon monoxide gas, which burns at the orifice in the cover so long as reduction is taking place. ”

“ The carbons are thus kept always at the same distance apart, and the light playing between them is thus rendered constant without the aid of complex regulators. In the experiments at the West India Docks the current was produced by a magneto-electric machine, worked by a small steam-engine, and the results are described as having been eminently satisfactory. For lights of small and medium size, an apparatus of even greater simplicity may be employed, the carbon points being dispensed with and nothing used beyond a piece of the so-called kaolin held between the electrodes. ”

“ Across this gap between the carbons an arc of light is seen, which in reality results from a series of electric sparks following each other in rapid succession. This arc, called the voltaic arc, is brilliant, but it is not from this arc that the chief part of the light comes. The ends of the carbon become intensely bright, being raised to a white heat. Both the positive and negative carbons are fiercely heated, but the positive is heated most. ”

“ The electrical energy is more evenly distributed, and the current can not so readily form a path of highest temperature, and consequently of least resistance through the mass along which the entire current or the bulk of the current can pass. The operation must necessarily be conducted within an air-tight chamber or in a non-oxidizing atmosphere, as otherwise the carbon will be consumed and act as fuel. The carbon acts as a deoxidizing agent for the ore or metalliferous material treated, and to this extent it is consumed, but otherwise than from this cause, it remains unimpaired. ”

“ 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 the ordinary incandescent electric lamp, the brilliant light is produced by a glowing filament of carbon. The powerful current of electricity experiences so much resistance as it flows through this badly conducting substance, that it raises the temperature of the carbon wire so as to make it dazzlingly white-hot. Indeed the carbon is thus elevated to a temperature far in excess of that which could be obtained in any other way. The reason why carbon is employed in the electric lamp, in preference to any other substance, may be easily understood. ”

“ Granulated carbon is used for it presents a large surface to the electrolyte, reduces the internal resistance of the cell, and therefore increases the current output of the battery.
As soon as the battery starts generating current, polarization begins, with the liberation of hydrogen gas. If the cell is discharged at a high rate, the manganese dioxide will be unable to absorb all of the gas, and consequently pressure will be erected within the cell. The greater the rate of discharge, the greater will be the amount of hydrogen set free, and the higher the pressure. ”

“ It will be noticed that only a small fraction of the current is carried by free carbon and oxygen atoms, showing that in phosgene the carbon and oxygen atoms are so firmly united that the greater part of them remain together even when the gas is dissociated. ”

“ 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. ”

“ I have four cells of carbon battery; the solutions are bichromate of potash and sulphuric acid. Also three cells of the Smee; sulphuric acid one part, to ten of water; and the four cells of the carbon battery are not sufficient to run my small electro-magnetic engine, for more than two or three minutes. I wish to know if it would be injurious to either one of the batteries if I should unite them both in one circuit, to run the engine, for about one or two hours at a time. A. The batteries will not be injured, but they will not work well together. Better increase the number of carbon elements. ”

“ Again the greater the charge the less the intensity, so that a line due to a quadruply charged carbon atom would be accompanied by a stronger line due to a triply charged atom, a still stronger one due to a doubly charged atom, while the normal carbon line would be the strongest of all. ”