- FURNACE
- used for baking tobacco-pipes. We may, be criticised for introducing into our plates the implements of so trifling a manufacture, but we shall excuse ourselves, on account of the ingenious structure of the furnace, and the application which may be made of it to other and more important purposes. This furnace is to be admired for the equality of the heat in every part of the crucible, or pot, in which the pipes, or other articles to be heated, are placed, at the same time that the flame is not permitted to enter, so as to soil the articles it contains. This crucible is marked A A, Plate III. figs. 4 and 5: it is of a cylindrical figure, terminated at the top by a hemisphere; it is placed over the fire place, B, and enclosed within a furnace, D D, of brickwork, lined with fire-brick E E: between this lining and the crucible is a space of about 4 inches, all round in which the flame from the fire-place circulates, without interruption, except what arises from the numerous supports which are necessary to sustain the crucible in its proper position; but as these are always placed edge-ways to the flame, and are very thin, they cause but little obstruction to its action: the supports are 12 ribs, between the crucible and the lining, which form the same number of flues, as shown by the dotted lines x, fig. 5, (the dotted circle A being the crucible): the ribs are perforated with occasional apertures, (see the section, fig. 4.) to connect one flue with the adjoining; but the principal bearing of the crucible is taken from five piers, b b c, formed of bricks, projecting one over the other: one of these piers, c, is placed at the back of the fire-place, and the other four at the sides b, b, and projecting at the top, nearly into the centre of the crucible, so as to support and strengthen the bottom of it, which rests upon these piers, the spaces between which form the mouths, or commencement of the flues surrounding the crucible: at the top of the crucible all the flues unite in the dome, L, of the fire-brick lining, and this has a circular opening through it, leading into the chimney N.
The lining, F E E, of the chimney is open on one side, (see the plan), to form the door, at which the pipes are taken in and out of the furnace; the opening is permanently closed as high as k, fig. 4, by an iron plate plastered with fire-clay; above this is left open, and only closed when the furnace is burning by temporary brick-work: when this is removed, the furnace can be filled or emptied through the opening; and, for this purpose, the crucible has a similar opening in its side: when the furnace is burning, this aperture is closed, by an ingenious contrivance: the workman first spreads a layer of clay round the edge of the opening; he then sticks the stems of broken pipes across, from one side to the other, and plasters the interstices with clay in a manner exactly similar to the lath and plaster used in building. The whole of the crucible is made in this manner; the bottom is composed of a great number of fragments of pipes, radiating to the centre; these are coated with a layer of clay at the circumference; a number of the bowls of broken pipes are inserted into the clay: in these other fragments are placed upright, to form the sides of the crucible. The ribs round the outside, which form the flues, are constructed in the same manner, as is also the dome, L, of the fire-brick lining; by this means the crucible can be made very strong, but at the same time so thin, as to require but little clay to construct it, and is less liable to split by the heat, than a vessel formed of thicker materials. This method might, we think, be advantageously applied in other cases, where a very thin vessel or lining is required for a furnace. The pipes which are to be baked are arranged within the crucible, as shown in the section, the bowls resting against the circumference, and the other ends supported upon circular pieces of clay, r, which are set up in the centre for that purpose; six small ribs are made to project inwards, all round the crucible, at the proper heights, to support the different ranges of pipes, without having so many resting upon each other, as to endanger their being crushed by the weight. By this mode of arrangement, the furnace is made to contain 50 gross, or 7200 pipes: these require to be burned from seven to nine hours; and the heat is at first brought on gently, and afterwards increased to the full heat required for baking this species of pottery: the fire is regulated by a simple kind of damper applied over the aperture in the dome, L, of the fire-brick lining. This is a mixture of horse-dung, sand, and pipe-clay, well worked together, and spread in thin layers upon coarse brown paper: a sheet of this being laid over the hole in the dome, so as to cover more or less of it, will give the means of increasing or diminishing the draught, and consequently, the heat of the furnace' (Rees 1972 ed. V3, 31-2).
- 'Pipe, Tobacco,
- ...The clay is found in the isle of Purbeck, in Dorsetshire, and is distinguished from others by its perfect white colour, and its great adhesion to the tongue when baked, occasioned by its great affinity for water: even in the raw state it has this property in a small degree. The clay is prepared by dissolving it in water in large pits, and the solution being well stirred, is run off into another pit, where it deposits the clay, which, when the water has become clear and run off, is taken up for use, all impurities of small stones, sand, &c. being separated from it and left in the first pit. The clay is now divided into portions, each sufficient to form one pipe, which are rolled on a table, under the hand, into long rolls, each with a bulb at the end, to form the bowl; and these are laid by for a day or two, to dry sufficiently for the pressing. This is done in an iron mould, consisting of two halves, which when put together leave a cavity of the shape of a pipe; a wire is thrust up the roll of clay, to form the bore of the pipe, and in this state it is placed between the two halves of the mould, which are then put into a kind of press or vice, by the screw of which the two halves are forced together, and the figure of the pipe imprinted on the clay included between them; a lever is next brought down, which is so situated as to introduce a stopper into the bowl of the pipe whilst still in the mould, and force it down sufficiently to form the cavity thereof: the wire is thrust backwards and forwards, to prick the tube completely into the bowl; it is then wholly withdrawn, the parts of the mould separated, and the pipe taken out, the superfluous clay removed with a knife, and they are laid up to dry a day or two, after which they are scraped and polished with a piece of hard wood, the tubes of the pipes curved as they are intended to be, and they are then carried to the furnace to bake, which is done in seven or eight hours for fifty gross of pipes.' (From Rees's Cyclopaedia).
