Carbide

“ As a general rule the water to carbide generator requires a larger gas holder than the carbide to water type because of the greater amount of carbide being acted upon by the water at any one time, also because the surface of carbide presented to the moist air within the generating chamber is greater with this type. ”

“ Calcium carbide is a hard, porous, grayish-black or bluish-gray incombustible material somewhat crystalline in form, odorless and unchangeable in a dry atmosphere, but when subjected to moisture gives off more or less acetylene gas. Carbide cannot be ignited and when well packed to prevent its coming in contact with water it is safe as regards all the conditions of transit and storage. ”

“ Experience tends to show that they may be employed, first, provided they are designed to take granulated carbide--which in comparison with larger grades is much more uniform and cylindrical in shape--and secondly, provided the quantity of carbide in the hopper does not exceed a few pounds. ”

“ 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. ”

“ As the ratio of cubical contents to superficial area of a lump is greater as the lump itself is larger, and as only the outer surface of the lump can be attacked by the water in the shoot during its descent, carbide for a hand-fed carbide-to-water generator should be in fairly large masses--granulated material being wholly unsuitable--and this quite apart from the fact that large carbide is superior to small in gas-making capacity, inasmuch as it has not suffered the inevitable slight deterioration while being crushed and graded to size. ”

“ Foreign makers break and blend ingot and crust to standard size, the best makers guaranteeing their carbide ninety per cent pure, giving five cubic feet of acetylene per pound (pure carbide gives 5.89 cubic feet) . Eight to nine pounds of carbide per horse power in twenty-four hours, averaging five cubic feet of acetylene, is considered satisfactory work. The Union Carbide Company, which controls the sale of carbide in the United States, is selling graded carbides under guarantee, the first grade being the nearly pure ingot, the lower grade the crust. ”

“ Calcium carbide is a compound of calcium and carbon. Calcium is a white metal not found in the natural state, but exists chiefly as a carbonate of lime, which is ordinary limestone, including the various forms of marble. As a pure metal it is hard to obtain and very hard to maintain, as it readily oxidizes when in contact with the air. The symbol for calcium carbide is CaC2, which means that a molecule of this carbide is compounded of one atom of calcium and two atoms of carbon. ”

“ One cubic metre of acetylene is compressed to two litres in liquid form; two litres of carbide weigh 4.44 kilogrammes, which will produce a cubic metre and a third of acetylene, reckoning three hundred litres to the kilogramme, which is the average guaranteed yield of carbide. The light tin carbide cans occupy less space and weigh less than the heavy steel cylinders, while the generation of the gas is simple and, with proper generators, perfectly safe. ”

“ When carbide is acted upon by water considerable heat is evolved; indeed, the action develops about one-twentieth of the heat evolved by the combustion of carbon. As, however, the temperature developed is a function of the time needed to complete the action, the degree of heat attained varies with every form of generator, and while the water in one form may never reach the boiling-point, the carbide in another may become red-hot and give a temperature of over 800° C. Heating in a generator is not only a source of danger, but also lessens the yield of gas and deteriorates its quality. ”

“ Although at the present time a marvellous improvement has taken place all round in the quality of the carbide produced, the acetylene nearly always contains minute traces of hydrogen, ammonia, sulphuretted hydrogen, phosphuretted hydrogen, silicon hydride, nitrogen and oxygen, and sometimes minute traces of carbon monoxide and dioxide. The formation of hydrogen is caused by small traces of metallic calcium occasionally found free in the carbide, and cases have been known where this was present in such quantities that the evolved gas contained nearly 20% of hydrogen. ”

“ 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. ”

“ If, then, the opposite system of construction is adopted, and carbide is fed into water mechanically, no after-generation can take place; and provided the make of gas can be controlled in a small carbide-feed generator as accurately as is possible in a small water-to-carbide generator, the carbide-feed principle will exhibit even greater advantages in portable apparatus than it does in plant of domestic size. ”

“ At temperatures between about 900° and 1100° the carbon exists in the form of carbide of iron dissolved in the iron, at a temperature of 890° the iron which can exist in different forms as an allotropic substance passes from the γ form to the β form, and in this form cannot dissolve more than .9 per cent, of carbon as carbide. Thus at this temperature a large proportion of the carbon passes out of the solution. ”

“ 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.
Agricultural chemistry is another one of the practical developments of the Nineteenth Century. A hundred years ago the farmer planted his crops, prayed for rain, and trusted to Providence for the increase ”

“ To conduct water to the carbide it necessarily had to extend to the carbide receptacle and as necessarily had to penetrate the carbide if the rod located in it, whether straight or bent, was to act 'in the nature of a stirrer, which on proper manipulation' might 'be used to break up the mass of carbid surrounding the outlet of the water duct,' which is the purpose that the patent ascribes to it. ”

“ When a manufacturer strives to give his carbide the highest gas-making power possible he frequently increases the proportion of carbon in the charge submitted to electric smelting, until a small excess is reached, which remains in the free state amongst the finished carbide. After decomposition the fine particles of carbon stain the moist lime a bluish grey tint, the depth of shade manifestly depending upon the amount present. ”

“ Commercial carbide is essentially an American discovery, and it was developed industrially by Willson's associates before industrial action began abroad. Messrs. Dickerson and Suckert, of New York, were the first to undertake the industrial liquefaction of acetylene. Dr. G. de Chalmot, chemist, and Mr. J. M. Morehead, electrician, worked up the details of the furnace process in the early days at Spray, North Carolina, and the purity and the yield from a given weight of material of their carbide have never been excelled, though cheaper working furnaces are now in use. ”

“ This has been followed by a sudden descent of all the carbide in the store into the water beneath, and the evolution of gas has sometimes been too rapid to pass away at the necessary speed into the holder. The trouble is rendered even more serious should the whole charge of carbide fall at a time when, by neglect or otherwise, the body of the generator contains much lime sludge, the decomposition then proceeding under exceptionally bad circumstances, which lead to the production of an excessively high temperature. ”

“ These contend that the so-called beta iron and martensite are only decomposition or transition forms of gamma iron and austenite.
Two or three other theories have been more or less strongly advocated but these also suffer from lack of evidence. The one which perhaps ranks next in number of advocates is the “carbon theory.” Its supporters contend that by quenching, alpha iron is made to hold carbon or iron carbide in solid solution and that it is this solution of carbon or carbide which gives to the steel hardness in proportion to its carbon content. ”

“ Manifestly the defect is chiefly, if not always, to be noticed in the working of carbide-to-water generators. The phenomenon has been examined by Mauricheau-Beaupré, who finds that frothing is not characteristic of pure carbide and that it cannot be attributed to any of the impurities normally present in commercial carbide. ”

“ The metallic oxide is reduced; the metal unites with the carbon, producing a crystalline carbide, and the oxygen combines with the calcium to form lime. By this method M. Moissan has obtained crystallized carbides of aluminum, manganese, tungsten, molybdenum, titanium, and chromium. In case the metal does not give a combination with carbon, it is obtained in free state as a melted button. There have been reduced in this way by carbide of calcium, to form free metals, the oxides of lead, bismuth, and tin. ”

“ The amorphous carbide, which was at first a waste product, has been tried, it is reported, with success as a lining for steel furnaces, as it is said not to be affected by iron or iron oxide at a white heat. ”

“ In charging the generating chambers of water-feed machines clean all residuum carefully from the containers and remove it at once from the building. Separate from the mass any unslacked carbide remaining and return it to the containers, adding now carbide as required. Be careful never to fill the containers over the specified mark, as it is important to allow for the swelling of the carbide when it comes in contact with water. The proper action and economy of the machine are dependent on the arrangement and amount of carbide placed in the generator. Carefully guard against the escape of gas. ”

“ 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 ”

“ While this carbon or iron-carbide solid solution may and probably does itself confer additional hardness to the steel, its main function is to retard or slow down the change from gamma into beta and alpha iron, which change in carbonless iron and low carbon steels is so insistent and extremely rapid that not even the most severe quenching, as in ice-water or liquid air, can prevent or stop it. ”

“ If the carbide charged into a hand-fed generator is in very large lumps there is always a possibility that overheating may occur in the centre of the masses, due to the baking of the exterior, even if the generator is fitted with a reaction grid. Manifestly, when carbide in lumps of reasonable size is dropped into excess of water which is not merely a thick viscid cream of lime, the temperature cannot possibly exceed the boiling-point--i.e., 100° C.--provided always the natural convection currents of the water are properly made use of. ”

“ 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 cheap production of this material and the easy liberation by its aid of acetylene at once gave the gas a position of commercial importance. In the manufacture of calcium carbide in the electric furnace, lime and anthracite of the highest possible degree of purity are employed. A good working mixture of these materials may be taken as being 100 parts by weight of lime with 68 parts by weight of carbonaceous material. ”

“ It is easy to imagine that the carbide container of a small generator might be so large, or loaded with so small a quantity of carbide, or that the apparatus might in other respects be so badly designed, that the gas evolved might contain a sufficient proportion of air to render it liable to explode in presence of a naked light, or of a temperature superior to its inflaming-point. ”

“ 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 ”