Recent patents. (Oxide of Zinc.)

The London Journal of Arts, Sciences, and Manufactures, and Repertory of Patent Inventions.

Conducted by Mr. W. Newton, of the Office for Patents, Chancery Lane. (Assisted by several Scientific Gentlemen.)

VOL. XXXVI. (Conjoined Series.)

London: Published by W. Newton, at the office for patents, 66, Chancerylane, and Manchester; t. and W. Piper, Paternoster Row; Simpkin, Marshall, and Co., Stationers' Court; J. McCombe, Buchanan St., Glasgow; and Galinani's Library, Rue Vivienne,

Paris. 1850

To Charles Andrè Felix Rochaz, of New-court, Saint Swithin's-lane, in the City of London, merchant, for improvements in the manufacture of oxide of zinc, and in the making of paints and cements when oxide of zinc is usedused.— [Sealed 28th February, 1849.]

The distinctive character of this invention consists, first, in improvements on the furnaces and apparatus employed in manufacturing oxide of zinc, whereby white oxide of an uniformly perfect quality is obtained from the whole of the zinc, which is introduced into the apparatus either in a mineral or metallic state; secondly, the invention consists in obtaining, by the mixture of such white oxide of zinc with certain substances, a good bodied paint or pigment; and, thirdly, the invention consists in making cements, as hereafter explained, when using oxide of zinc.

PLATE I. Rochaz's Apparatus for Making Zinc White.

In Plate I., fig. 1, is a vertical section of the improved furnace for converting zinc into white oxide; and fig. 2, is a vertical section of the same. a, a, are crucibles of fire-clay, with flat moveable covers, having at their centre a round aperture; b, b, are pillars of fire-brick, supporting the crucibles; c, c, are moveable slabs of fire-clay, serving as a roof to the furnace (which roof can be taken off when the crucibles are to be cleansed or replaced); d, is the opening of the fire-place; e, the ash-pit; and f, is the part of the furnace whereon the chimney is placed. g, are flues for conducting off the gases from the fire-place; d, is the fire-grate; and f, are iron bars, supporting the grate. g, is a longitudinal flue, which receives the products from all the flues g; and h, is a space where the combustion of the vapours of zinc takes place, and which communicates, by the opening w, with the chamber k, l, where the oxide deposits itself. r, is the door of the chamber; and m, are sheets of iron or zinc, fixed across the chamber. n, n, are bands of hemp or other textile substance, hanging from the roof of the chamber in transversal rows, a short distance from each other, and at crossed intervals; so that the current, after passing through the spaces of one row, meets perpendicularly the bands of the next row. The lower ends of those bands are fixed on a piece of wood s; the upper ends of the bands come through the roof or ceiling, where they are fastened, and their ends enter into a zinc trough t, which contains water; and, in order to be able to shake the bands, from time to time, a rope or cord is fixed at each end of the piece of wood,—such ropes or cords being carried up through the ceiling, to allow of the workman raising and lowering the piece of wood, so as to shake the bands and free them from the oxide which has settled upon them.

Three or four of these systems of rows or curtains of bands will generally be sufficient; but their number, and that of the rooms or compartments l, with or without metallic screens, can be multiplied; and the last room or compartment has an opening or chimney, with a register for the regulation of the draft.

The first compartment of the chamber is constructed of masonry or sheets of metal, on account of the high tempera ture created there by the air and oxide on their issuing from the furnace; but there is great advantage in constructing the other rooms or compartments entirely of sail-cloth or other similar fabric; because then any the most convenient shape and dimensions, according to the particular premises, can be given to such chambers or rooms; and, especially, be cause it will then be easy to keep the roof and sides of this part of the apparatus constantly and abundantly watered, which is desirable. The oxide adheres more easily to the sides and bands, it falls quicker, and takes less space, and it can be detached from the roof and sides by simply beating them externally.

The mode of carrying on the operation is as follows: — The crucibles are first filled with metallic zinc, and the covers are placed on them; the openings u, are then stopped with bricks; and the fire is urged until the metal begins to subli mate: the bricks are then to be removed from the openings u. The vapours issuing from the aperture of the cover ignite and oxidize by the contact of the air in the spaces h, h, h; the currents rushing in carry the products through the opening u, u, into the chamber k, where they encounter the metal lic partitions m, which compel them to descend and rise again before they pass into the part l, through the free space left between the roof and the partition wall; and, after meeting with another metallic screen m, they traverse in suc cession a series of rows of moistened bands. The oxide settles on the roof, floor, sides, and other parts of the whole of the range of compartments; while the current, containing but an insignificant portion of oxide, issues out at the chim ney. The crucibles are to be fed with molten zinc from time to time. At the beginning of the operation it is well to keep the covers on the crucibles, in order to increase the heat; but as soon as the whole of the furnace has become well heated by the flames of the fire underneath, and of the burning zinc, the covers may be removed. The vapours are evolved in greater quantity, and the operation goes on more rapidly; but during the whole of the operation, from the moment the zinc flames have begun to appear, concretions form themselves around the borders of the crucibles, or the orifice of the covers: these concretions are formed of oxide, which has not been carried away by the current. That oxide, alone, which is carried by the current into the chamber, is of good quality, while that which remains is coarse. The workmen should be careful to keep the orifices free from such concretions by means of a scraper, and to remove them, from time to time, from the furnace. This residuum is afterwards treated in the following manner: — It is first mixed with pulverized charcoal or coke, and the mixture is moistened and moulded into small cakes, or in a form similar to that of the interior of the crucibles. These are to be placed in the crucibles, and treated as has been done with regard to the metal, with this difference, that the covers are to remain all the while on the crucibles. The shape of the crucibles may be varied: the patentee prefers them to be made shallow when only treating metal zinc; but when the residuum is also to be operated on by the same crucible, he prefers the shape shewn in the drawing. The process, above described, is accelerated and improved by forcing a thin sheet of hot or cold air on the surface of the melted and burning metal in the crucibles or pans;—this is done by adjusting to the mouths of the furnaces a door, which has, at the lower part, an aperture for the passage of the flat tuyere. This blast, by impinging on and sweeping over the surface of the metal,' diminishes materially the formation of concretions, and increases that of the vapours; while, at the same time, a minimum of air being admitted, the force of the current in the chamber is reduced, which saves the loss of oxide at the chimney. The peculiar character of this part of the invention consists in obtaining spaces h, over the crucibles or vessels a, as explained; also causing streams of air to impinge on the melted zinc; also the using of rows of bands; and likewise the using of woven fabrics in making the rooms or chambers.

The furnace, above described, could be used in the fabrication of oxide by the direct process, viz., the treatment of zinc ores; but the number of furnaces required would be great, as the crucibles hold but a limited quantity, and cannot be placed one over the other; he therefore prefers to use, for the treatment of zinc ores, two sorts of furnaces,—the first of which is based on the disposition of the crucibles in the Belgian method of distillation of zinc, but is modified, as will now be described.

Fig. 3, is the front of a furnace for producing zinc-white from zinc ores, furnished with crucibles, and having an adjoining chamber for the reception of the oxide; and fig. 4, is a vertical section, taken through the middle of the furnace. a, are the crucibles or retorts; b, are slabs of fire-clay, under thinner slabs of cast-iron; g, are pillars of fire-clay, separating the crucibles and supporting the slabs; i, are stoppers intended, during the charging and cleansing of the crucibles, to stop the openings of the passages into the chamber k, such as before described; and m, are metallic sheets, as in the former apparatus. At fig. 4, c, are stoppers, forming, with the front of the furnace and the upper and under slabs, the fourth side of the square spaces for oxidation, which open into the chamber k, by apertures left in the wall of the same areal section as the passages d, for oxidation; r, is the chimney; e, the ash-pit; d, the grate; and/, are iron bars sup porting the grate. The compartments for receiving the oxide are similar to those above described.

The mode of operating is as follows: — When the crucibles or retorts have been filled with ore, roasted, and mixed with charcoal or coke, as usual, the stoppers ai, which are made to fit in the orifice of the crucibles, are put in and luted all round, except at the upper part, where a slope exists for the passage of the vapours. As soon as the flames, issuing from that slope, assume the whiteness of zinc flames, the stoppers i, (fig. 3,) are to be removed, and the passages d, for oxidation, are to be formed by putting in the longitudinal stoppers c, (fig. 4,) and luting them externally. The currents of air, entering at the further ends of the passages d, inflame the va pours and carry the oxide into the chamber K. During the whole of the operation a workman takes care to clear the apertures of the stoppers a1, by means of an iron rod, crooked at one end: the concretions fall on the sole of the passages d, and are drawn out, from time to time, by the workman, who also pushes into the chamber k, the oxide which deposits itself in that part of the passages formed by the openings into the chamber k.

The cleansing and charging of the crucibles are effected in the manner well known to zinc-makers, as the Belgian method for distilling zinc; and the operation, when properly conducted, and with good ores, can be effected three times in 24 hours. The oxide, thus produced, is said to be in no way inferior to that obtained from the metal in the manner first described; but as, for the first hour after charging, the vapours are slow in evolving, and are mixed with foreign matter, it is advisable, during this period of the distillation, to collect the products apart, in order to preserve the uniformity of the general result. For this purpose, instead of the stoppers a1, with slopes, which have been described, the retorts are each to be provided with a stopper, having a prominent ledge, to which is to be adapted a tube, similar to those used in the distillation of zinc. In this case, the stoppers c, (fig. 4,) are only to be put in one hour after the charging; then the tubes are to be taken off, and the stoppers I, are to be removed. In these tubes the zinc is collected in a metallic or in a grey oxide state. This mode of treatment is simple and economical, as it possesses not only the advantage of saving almost the whole of the expense of reducing zinc to its metallic state, but also of collecting that considerable quantity of oxide which, in the distillation of ores for the production of blue metal, oozes out, and is lost through various parts of the apparatus. The peculiar character of this apparatus consists in the arrangement of passages d, for oxidizing the zinc vapours, and conducting them into the chamber k.

Another method, which offers a great saving in fuel and other expenses, is described as follows: — Fig. 5, is a vertical section of a blast furnace, for obtaining zinc-white from zinc ores. a, a, are two passages, to receive the ores mixed with the fuel; b, b, are two passages, to receive charcoal or coke; c, are covers of the passages; and d, is a flue of oxidation, leading into the chamber k. The part e, will, at all times, be full of charcoal or coke; the part f, is where the reduction and sublimation take place; G, is a cavity, into which the slags and residuum descend; h, tuyers; and a, is a moveable stopper in the oxidizing passage.

The following is the operation: — The ores, properly roasted and ground, are mixed with the usual proportion of coke or charcoal; and, when necessary, flux is to be added. The whole is afterwards moistened and shaped into small bricks or cakes, which are well dried. When the fire has been kept up for some time with pure coke, and the furnace well heated, the mixture of ores and fuel is to be introduced into the passages a; and the passages b, are to be filled with charcoal or coke. The blast of air, whether hot or cold, is forced in at the tuyers h, h: the volatile products find an outlet as soon as the stopper a, is removed. The vapours of zinc burn at that opening, and the oxide is carried through the passage or flue d, into a chamber K, such as above explained. The residuum of the production, and the lead, if there be any, contained in the ores, are drawn out through an aperture at the lower part of the cavity g. The peculiarity of this apparatus lies in the functions of the passages b, which form constantly a bed of incandescent coke in the part e, through which the gases and vapours have to find their way; and hence the vapours, which may have partially become oxidized by the excess of air supplied by the blast, are again reduced, and reach the opening a, in a pure state. When necessary, the patentee places, at the opening a, fire-clay partitions or divisions, so arranged as to stop or intercept the ashes or other particles of foreign matters which may be mixed with the gases and vapours. With respect to this part of his invention, the patentee remarks, that zinc-white has before been made; and various furnaces have been employed for such manufacture; and it has been proposed to use a blast furnace of an ordinary con struction for such purposes;—he does not therefore claim the making of oxide of zinc, but only the peculiarities in the furnaces and apparatus herein described.

For the manufacture of zinc-white paints and pigments, the patentee combines zinc-white (in preference) with white marble, ground to an impalpable powder; and, when that substance cannot be procured, he supplies its place by having quick-lime exposed, under shelter, for a sufficient time for it to slake itself gradually, by slowly imbibing the water and carbonic acid of the atmosphere. He states that, if the hydrate of lime were employed shortly after it had been simply slaked, it would preserve an objectionable degree of causticity; but when that causticity has disappeared, in consequence of gradual saturation by carbonic acid, the hydrate becomes the best substance which can be united with zinc-oxide; and the lime may be combined at the rate of from twenty-five to thirty per cent.

Another improvement in the preparation of paint, where zinc-oxide is used, consists in adding to this oxide, or to its mixtures with other bases, rosin or resinous matters,—turpentine and drying-oil being preferable. By diluting the whole in a sufficient quantity of spirits of turpentine to bring it to the degree of fluidity which may be required, a solid, fresh, unalterable paint is produced, which dries very quickly, and can endure the most frequent wasbings. The following are the proportions recommended: — For brilliant paint—to twenty parts, by weight, of base, six parts of rosin, two parts of turpentine, and one part oil, are added. For flat paint—to twenty parts of base, three parts of Burgundy pitch and one part of oil are added. In manufacturing cements, when zinc is used, the patentee takes the residuum from the crucibles, pots, or retorts, used in the manufacture of zinc, or of oxide of zinc, and mixes it with common mortar in the construction of walls and buildings: — the addition of such matter communicates to the mortar a high degree of hardness.

—[Inrolled August, 1849.]

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