Calcium carbide

“ The metallic carbides are crystalline solids, the greater number being decomposed by water into a metallic hydrate and a hydrocarbon; sometimes hydrogen is also evolved. Calcium carbide owes its industrial importance to its decomposition into acetylene; lithium carbide behaves similarly. Methane is yielded by aluminium and beryllium carbides, and, mixed with hydrogen, by manganese carbide. The important carbides are mentioned in the separate articles on the various metals. The commercial aspect of calcium carbide is treated in the article Acetylene. ”

“ This is due to two causes: first, however carefully it be stored, carbide deteriorates somewhat by the attack of atmospheric moisture; and since the superficies of a lump (where the attack occurs) is larger in proportion to the weight of the lump as the lump itself is smaller, small lumps deteriorate more on keeping than large ones. The second reason, however, is more important. Not being a pure chemical substance, the commercial material calcium carbide varies in hardness ”

“ It is found that the ingot of calcium carbide formed in the furnace, although itself consisting of pure crystalline calcium carbide, is nearly always surrounded by a crust which contains a certain proportion of imperfectly converted constituents, and therefore gives a lower yield of acetylene than the carbide itself. ”

“ Calcium carbide resembles coke in general appearance, and it is used for the manufacture of acetylene gas, for which purpose it is only necessary to immerse the calcium carbide in water, and the gas is at once given off by the mutual decomposition of the water and the carbide.
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“ In the first place, calcium carbide itself is a very bad conductor of heat. So deficient in heat-conducting power is it that a lump a few inches in diameter may be raised to redness in a gas flame at one spot, and kept hot for some minutes, while the rest of the mass remains sufficiently cool to be held comfortably in the fingers. In the second place, commercial carbide exists in masses of highly irregular shape, so that when they are packed into any vessel they only touch at their angles and edges ”

“ To fix the nitrogen in the carbide it is necessary to cool the latter after it comes from the electric furnaces and grind it to a very fine powder. This powder is then placed in furnaces that look like steel barrels but are three or four times larger than an ordinary barrel. The oven filled with calcium carbide is then electrically heated with a carbon rod running through the center. When the temperature is about as hot as that of molten iron the pure nitrogen gas from the liquid air plant is pumped in and allowed to act on the calcium carbide for about a day and a half. ”

“ Calcium carbide is crushed by the makers into several different sizes, in each of which all the lumps exceed a certain size and are smaller than another size. It is necessary to find out by experiment, or from the maker, what particular size suits the generator best, for different types of apparatus require different sizes of carbide. ”

“ He also made the corresponding sodium compound and showed that it evolved the same gas, whilst in 1862 F. Wohler first made calcium carbide, and found that water decomposed it into lime and acetylene. It was not, however, until 1892 that the almost simultaneous discovery was made by T. L. Willson in America and H. Moissan in France that if lime and carbon be fused together at the temperature of the electric furnace, the lime is reduced to calcium, which unites with the excess of carbon present to form calcium carbide. ”

“ Just as, by an immutable law of chemistry, a given weight of calcium carbide yields a given weight of acetylene, and by no amount of ingenuity can be made to produce either more or less; so, by an equally immutable law of physics, the decomposition of a given weight of calcium carbide by water, or the decomposition of a given weight of water by calcium carbide, yields a perfectly definite quantity of heat--a quantity of heat which cannot be reduced or increased by any artifice whatever. ”

“ In the absence of water, calcium carbide is as inert a substance as can well be imagined: it cannot be made to catch fire, for it is absolutely incombustible, and it can be heated in any ordinary flame for reasonable periods of time, or thrown into any non-electrical furnace without suffering in the least. But in presence of water, or of any liquid containing water, matters are different. ”

“ Calcium carbide is made at Niagara Falls by placing an intimate mixture of about three parts of powdered quicklime to two parts of powdered coke into an electric furnace of the so-called arc type. The current of electricity generates an intense heat which chemically combines the calcium of the quicklime with the carbon of the coke, the oxygen of the quicklime uniting with some of the carbon to form carbon monoxide gas which escapes. ”

“ Pure crystalline calcium carbide yields 5.8 cubic feet of acetylene per pound at ordinary temperatures, but the carbide as sold commercially, being a mixture of the pure crystalline material with the crust which in the electric furnace surrounds the ingot, yields at the best 5 cubic feet of gas per pound under proper conditions of generation. ”

“ Calcium carbide is a body which evolves an inflammable, or on occasion an explosive, gas when treated with water; and therefore its presence in a building has been said to cause a sensible increase in the fire risk because attempts to extinguish a fire in the ordinary manner with water may cause evolution of acetylene which should determine a further production of flame and heat. In the absence of water, calcium carbide is absolutely inert as regards fire ”

“ The two principal processes utilized in making calcium carbide by electrical power are the ingot process and the tapping process. In the former, the anthracite and lime are ground and carefully mixed in the right proportions to suit the chemical actions involved. The arc is struck in a crucible into which the mixture is allowed to flow, partially filling it. An ingot gradually builds up from the bottom of the crucible, the carbon electrode being raised from time to time automatically or by hand to suit the diminution of resistance due to the shortening of the arc by the rising ingot. ”

“ As calcium carbide evolves an inflammable gas when it merely comes into contact with water, it becomes possible to throw into the sea or river, by hand or by ejection from a mortar, a species of bomb or portable generator which is capable of emitting a powerful beam of light if only facilities are present for inflaming the acetylene generated; and it is quite easy so to arrange the interior of such apparatus that they can be kept ready for instant use for long periods of time without sensible deterioration, and that they can be recharged after employment. ”

“ Let the reader drop a piece of calcium carbide as large as a small marble into a little water in a cup; there is a rapid action, a gas (acetylene) is given off, which burns with a smoky flame if a lighted match is held over the cup. (The experiment should be tried in the open air.) So much heat is generated in the reaction that the cup becomes hot. Nearly four per cent, of the earth's outer crust is calcium ”

“ Neither material is altogether free from objection, the cyanamide heating when mixed with other manures and even with soil, and being liable to give off acetylene gas owing to the presence of calcium carbide, whereas the calcium nitrate is a salt which on exposure to a moist atmosphere readily deliquesces. ”

“ Inasmuch as acetylene is produced by the mere interaction of calcium carbide and water, that is to say, by simply bringing those two substances in the cold into mutual contact within a suitable closed space, and inasmuch as calcium carbide can always be purchased by the consumer in a condition perfectly fit for immediate decomposition, the preparation of the gas, at least from the theoretical aspect, is characterised by extreme simplicity. ”

“ A mixture of lime and charcoal heated in an electric furnace will give us calcium carbide. This calcium carbide, with water, will give us acetylene, and the acetylene will combine with hydrogen to form ethylene. ”

“ Carbides of other metals can be made in the electric furnace, but, owing to the cheapness of the new material, calcium carbide is the only one of these which has industrial value as a source of acetylene. One pound of pure carbide yields 5.89 cubic feet of acetylene.
Thus far carbide has been found industrially valuable for two other purposes. The one is for carbonizing steel; experiments in Germany show that iron or soft steel takes up carbon more readily when it is heated with carbide than when it is heated with coal dust or charcoal. Some steel works are now using carbide for this purpose. ”

“ The argument is sometimes advanced that an acetylene generator containing carbide in excess will work satisfactorily without exhibiting an undesirable rise in internal temperature, if the vessel holding the carbide is merely surrounded by a large quantity of cold water. The idea is that the heat evolved in that particular portion of the charge which is suffering decomposition will be communicated with sufficient speed throughout the whole mass of calcium carbide present, whence it will pass through the walls of the containing vessel into the water all round. ”

“ The last generator impurity is lime dust, which is calcium oxide or hydroxide carried forward by the stream of gas in a state of extremely fine subdivision, and is liable to be produced whenever water acts rapidly upon an excess of calcium carbide. This lime occasionally appears in the alternative form of a froth in the pipes leading directly from the generating chamber; for some types of carbide-to-water apparatus, decomposing certain kinds of carbide, foam persistently when the liquid in them becomes saturated with lime, and this foam or froth is remarkably difficult to break up. ”

“ The difference in temperature between the acetylene and the carbide in Caro's test accentuates the difficulty of gauging the heat in a carbide vessel by mere external touch, and supplies experimental proof of the previous assertions as to the low heat-conducting power of calcium carbide and of the gases of the decomposing vessel. It must not be supposed that temperatures such as Lewes has found ever occur in any commercial generator of reasonably good design and careful construction ”

“ EFFECT OF HEAT ON CARBIDE.--Chemically speaking, no amount of heat possible of attainment in the worst acetylene generator can affect calcium carbide in the slightest degree, because that substance may be raised to almost any temperature short of those distinguishing the electric furnace, without suffering any change or deterioration. ”

“ Calcium cyanamide has assumed importance in agriculture since the discovery of its economic production in the electric furnace, wherein calcium carbide takes up nitrogen from the atmosphere to form the cyanamide with the simultaneous liberation of carbon. ”

“ Calcium carbide in quantities not to exceed six hundred pounds may be stored, when contained in approved metal packages not to exceed one hundred pounds each, inside insured property, provided that the place of storage be dry, waterproof and well ventilated and also provided that all but one of the packages in any one building shall be sealed and that seals shall not be broken so long as there is carbide in excess of one pound in any other unsealed package in the building. ”

“ Properties.—A freshly prepared surface of the metal closely resembles zinc in appearance, but on exposure to the air it rapidly tarnishes, becoming yellowish and ultimately grey or white in colour owing to the information of a surface layer of calcium hydrate. A faint smell of acetylene may be perceived during the oxidation in moist air; this is probably due to traces of calcium carbide. It is rapidly acted on by water, especially if means are taken to remove the layer of calcium hydrate formed on the metal; alcohol acts very slowly. ”

“ Thomas L. Willson discovered the cheap process for the manufacture of carbide of calcium upon a commercial scale, and the new industry became placed upon a firm footing, it was only natural that the inventor should realize the possibilities of applying the new illuminant to the assistance of navigation. Acetylene gas gives a brilliant clear light of intense whiteness, which is286 capable of penetrating a great distance. Accordingly, he set to work to devise a buoy lighted by this gas, and able to carry sufficient storage of calcium carbide to burn for weeks or months without attention. ”

“ But in spite of his clumsiness the chemist is actually making things that he wants and cannot get elsewhere. The calcium carbide that he manufactures from inorganic material serves as the raw material for producing all sorts of organic compounds. The electric furnace was first employed on a large scale by the Cowles Electric Smelting and Aluminum Company at Cleveland in 1885. ”

“ Fortunately for Willson, among those to whom he had sent specimens of carbide was Lord Kelvin, the famous English physicist, whose reply to Willson, stating that the substance received was calcium carbide, was dated October 3, 1892, two months before Moissan's first publication. Borchers's claims are too vague to waste space on. Willson's priority is now generally recognized excepting in France. ”