Explanation of plate IV
The reader may have some idea of many of the AchTemical apparatus employed and mentioned in this work, it has been thought expedient to engrave them on one plate, whereby the whole may be seen at one view.
It is adviseable, that it be thoroughly committed to me-mory, which will save the tediousness of a frequent refe-rence, and give a quickness and facility in performing the operations themselves.
Fig. 1
A perpendicular section of a Cupel or Test: c the powdered bones kneaded with water, and firmly pressed into the iron ring, of which a section is seen at a b. There is a part at d which is hollowed, or dished out, for the re-ception of the metal to be tested.
Fig. 2
Fig. 3.
Fig. 4.
Fig. 5. Fig. 6.
A Muffel, in which all articles are placed which are to undergo the operation of a strong fire, free from smoke, such as enamelled work, stained glass, &c.
An Ingot-Mould, into the grooves of which melted metals are poured.
A Retort, made either of glass or earthen-ware, and used in various distillations.
A Crucible.
An Iron Cone, inverted, with a handle and foot, into which metals, and other results of opera¬tions, are occasionally directed to be poured.
Fig. 1.
Fig. 7.
A Reverberating Furnace.
a, The ash-hole door. b, The fire-place door.
c c c c, Registers, to regulate the heat.
d f The dome, or reverberatory,
e, The conical funnel.
f The retort in the furnace. gt The receiver.
h Iron bars to sustain the retort.
Fig. 8.
A Furnace for colouring Foils, where the hand represented in the act of performing the operation. See the article " Foil-making"
Fig. 9.
A long-necked Glass Alembic
A, The body of the matrass.
B, The neck of the matrass.
The head of the alembic.
Fig. 10.
Glass Alembic.
A The cucurbit.
BThe head
The aperture in the head, with the stopple.
D, The beak.
Fig. 11.
Bolt-head, or cap, which affixed on the upper opening of still. still of this kind nearly resembles the reverberating furnace ex-ternally, fig. 7. — which there the dome, may be supposed to be the upper half of the body of the still, the under half being hid within the cavity of the fire-place and in lieu of the conical funnel substituted the above bolt-head. The exact proportions between the opening of the still, and the neck of the bolt- head, are not preserved in the plate, because the furnace would be, by this, too large for the work, or, on the Contrary, the bolt-head would be too small.
Fig. 62
A Melting Furnace, with its parts, A. B* C. D. F, taken from " Cramer's Art of Assaying Metals." We shall be very particular in the account of this furnace, as it is extremely well constructed, and usefuL
Form and Dimensions of this Furnace.
The melting furnace is made of iron-plates, the inner surfaces of which are covered with lute*. The cavity of it may be formed according to an elliptical mould. 1st,.. Make a hollow ellipsis, the focusses 12 inches asunder, and the ordinate 5 inches long ; cut it off in both its focusses, that it may assume the figure A. 2dly, Make in the hollow body, near its lower aperture, four holes, eight lines in diameter, and directly opposite (c, c,). 3dly, Fasten two flat iron-rings (d,) almost an inch and a half broad, at both the upper and the lower inward edge of this oval cavity ; and fill the inside of it with small iron hooks, jutting out about six lines, and three or four inches distant from each other. These, together with the rings just mentioned, serve to fasten the lute. Thus will the body of the furnace be made : only you must add at the outside, two iron handles (e, e,) to be rivetted on each side of that may be taken hold of and moved. 4thly, Make the cover of the furnace, which may be formed like the part cut off from the ellipsis, see fg. B. Let this have an opening (b) made in four inches high, five inches broad at bottom, and four inches at the top and adapt to this an iron door, hung on hinges, to shut close, and having at the inside border fastened to answering exactly to the circumference of the door, and as promi¬nent inwardly as the thickness of the lute to be applied to
Lute will be described at large in the next article. : for the same purpose, let small iron hooks be fastened to the inside of the door, which is intercepted by the said border. And lest this cover should be burnt within by the force of the fire, you must cover the inside of it with the same lute ; therefore it must be likewise furnished with a ring and iron hooks, as was done to the part A. Besides this, you must fasten two iron handles on the outside of this cover (fig. B. c c,) : then a round hole must be made in the top of being three inches in diameter, prolonged into hollow tube (d) almost cylindrical, and few inches high, upon which an iron funnel may, in case of neces¬sity, be adapted. 5thly, The lining both of the body and cover of the furnace made of the same materials as be¬fore-mentioned. Moreover, you must make for this fur¬nace two moveable bottoms, viz. one to receive the ashes, and admit the air the other to serve for reductions. The first made with an iron plate, formed into hollow cy¬linder, open at top, and to be shut at bottom with an orbicular iron plate, as with basis, five inches high, of such diameter, as that may receive the inferior orifice of the body of the furnace (fig. A) the depth of half an inch, see fig. therefore, let an iron ring (c) half an inch broad, fastened on the inside of the said bottom, the distance of half an inch from its upper border, to support the body of the furnace put into it. Again, let this but- torn have square door, four inches high, and as many¬inches broad, that may be shut closely, that r ou may in¬crease or diminish the draught of the air, at pleasure. On the left side of this door, about half the height of the bottom, let round hole (d) be made, one inch and half diameter, to admit the pipe of the bellows when need requires. Next to this, let another bottom part be made of the same matter and figure as the foregoing let be likewise of the same diameter, but two inches higher, so as to be seven inches high. Let likewise have round similar iron ring below its upper border, to support the bod body of the furnace to be received in it. But let a hole, two or three inches broad, and one inch high (fig. D. c,) be cut out just below the ring in the side of this bottom part; and let another round hole be made in the left side of this first hole, fit to admit the pipe of the bellows (d). Further, let another round hole like the foregoing (e) be made on the right, one inch from the bottom : then let the whole inside of this bottom part (the part above the ring excepted) be over-laid with lute, and a bed be made at the bottom, of a figure like, that represented by the line (f, g, h,). The matter of which this is made is common lute pulverized, passed through a sieve, and mixed with such a quantity of sifted charcoal dust, as may be lightly coherent, when moistened, mixed together, and pressed down. Of this matter the bed is made at bottom, like a segment of a sphere, having in the middle a small cavity somewhat lower, and made extremely smooth.
Use of this Furnace, This furnace is chiefly fit for fusions, which may be made in with or without vessels. When you are to melt with a vessel, put the body of the furnace (fig. A.) upon the first bottom (fig. C\) which has door to to open or. hinges introduce two iron bars through the holes of the furnace, (fig. A. c, c,) put upon them the iron- grate, which you are to introduce through the upper mouth of the furnace then put in the middle of this grate brick or square tile, very smooth, warmed, and dry otherwise, the vessels put upon especially the large ones, are easily split by the moist vapours coming out of by the heat. Let the height and width of these be small matter broader and higher than the bottom of the crucible or vessel set up'on for were less high, the bottom of the vessel could not be sufficiently warmed
and were less broad, the vessel might easily fall from it : then put upon this tile the vessel containing the matter to be melted, and surround it immediately with coals on every side, which must be ranged with care.
The fire is governed and regulated by opening or shutting the door of the ash-hole (fig. C. b) ; you may excite by putting the cover (fig. B) upon the body of the fur¬nace and besides, you put funnel upon the cylin¬drical mouth (d) of this cover, the melting fire becomes
still more violent but you moreover introduce the bel¬lows through the hole of the bottom part (fig. C. and the joint of the furnace with the bottom part and the door of the ash-hole (unless can be stopped very close of itself) be tightly closed with Windsor loam, the fire may be excited to so powerful degree, as to surpass the heat of smith's forge. Another advantage of this me¬thod that the vessels are not so easily broken, because the blowing of the bellows cannot affect them immedi¬ately, and because fire perfectly equal excited on every side. One may easily examine with this apparatus, how stones are affected the violence of the fire only. Now, you have mind to perform any operation with¬out vessel, and with naked fire for instance, to melt and reduce copper, tin, lead, and iron, or their ores the body of the furnace must be put upon the other pe- distals, having bed in (fig. D). However, you must, before this, open with knife the oblong hole (c), and the round one (d) of this bottom part, which are stopped with the lute sticking to the inside then you apply at the round hole (d), on the left side, the bellows, in such manner that the nozzle of being directed obliquely downwards, may blow strongly against the bed {f,g,h,) by this means, all the ashes that fall into the bed are blown away, and the strength of the fire determined to such degree, that all the melted bodies that fall into the said bed, remain in their state of fusion and were otherwise, the melted bodies would immediately wax vol. i, cold, and adhere in grains to the bed, whereas they ought to have melted into one regular mass. The oblong hole in the fore part of this bottom part (c) serves to discover, by means of a poker, whether the matter in the bed be melted or not : it serves likewise to take away through it whatever might stop the bellows, and in some cases to take away the scoria: then you put, first, coals into the furnace, one span high, and blow them well with the bellows, to make them burn, that the bed may be very hot before the matter to be melted is put in ; for if this is not previously done, the melted mass seldom runs into a regains, but remains dispersed among the scoria, which soon grow hard. The bed being well heated, and fresh coals added to the fire, put into it such quantity of the matter to be melted as cannot hinder the fire from being carried to the requisite degree ; which cannot be deter¬mined otherwise than by experience : again, put fresh coals, and upon them another quantity of the matter to be melted ; they may be, like strata, one upon another : but if the mass, once melted, could not long sustain the strength of the fire, or if you had a mind to melt a greater quantity of the matter than what can be contained in the bed, you must open the round lower hole (fig. D, e,) that you may make a channel passing from that hole through the lute, and reaching to the small cavity at the bottom of the bed (g) : to this hole, at the outside, apply an earthen dish like the bed within, or any other proper recipient, surrounded with burning coals, into which the matter melted, running from the bed through the hole «(fig. D. t) may be collected, as is represented by figure E.
Observation.
Furnaces of the foregoing description, together with crucibles, black-lead pots, and many other chemical appa¬ratus, were formerly imported, from Germany, at great cost and trouble. They are now made in England *, and with considerable advantages, being more portable, cheaper, and readier. A complete furnace, capable of being worked in a parlour chimney, may be had, from £. 3, to a higher cxpence, which will create little trouble, and will require no assistance from the bricklayer.
Of Lutes
In many chemical operations, the vessels must be co¬vered with something to preserve them from the violence of the fire, from being broken or melted, and also to close exactly their joinings to each other, to retain the sub¬stances which they contain when they are volatile and reduced to vapour. <For this purpose, several matters are employed, called in general lutes.
The lutes with which glass and earthen-ware retorts are covered, ought to be composed of nearly equal parts of coarse sand and refractory clay. These matters are to be well mixed with water and a little hair, so as to form a liquid paste, with which vessels are to be covered, layer upon layer, till it is of the required thickness. The sand mixed with the clay is necessary in this lute, to prevent the cracks which are occasioned by the contracting of clay during its drying, which it always does when it is pure. The hair serves also to bind the parts of the lute, and to keep it applied to the vessel ; for, notwithstanding the sand is introduced into some cracks are always formed, which would be likely to tumble off in pieces.
The lutes with which the joinings of vessels are closed, are of different kinds, according to the nature of the ope¬rations to be made, and of the substances to be distilled in They may be had, of all sizes and prices, of Mess. Pugh and Speck, at their manufactory, at the bottom of Booth Street, Spital Fields.
these vessels. When vapours of watery liquors, and such as are not corrosive, are to be contained, it is sufficient to surround the joining of the receiver to the nose of the alembic, or of the retort, with slips of paper or linen, covered with a tough paste of flour and water. In such cases also, slips of wet bladder, which will affix them¬selves close to the parts, are highly convenient. When more penetrating and dissolving vapours are to be contain¬ed, a lute is to be employed of quick-lime slaked by the air, and beat into a liquid paste with whites of eggs. This paste is to be spread on linen slips, which are to be ap¬plied exactly to the joining of the vessels. This lute is convenient ; it easily dries, becomes solid, and sufficiently firm. Lastly, when saline, acid, and corrosive vapours are to be contained, we must then have recourse to the lute called fat lute. This lute is made by forming into a paste some dried clay finely powdered, sifted through a fine lawn sieve, and moistened with water, and then by beat¬ing this paste well in a mortar with boiled linseed oil, i. e. linseed oil which has been made drying by boiling it with
litharge —sold by the colourmen. This lute will take and retain the form that is given it. It is generally rolled in cylinders of a convenient size. These are to be applied, by flattening them, to the joinings of the vessels, which ought to be perfectly dry, because the least moisture would prevent the lute from adhering. When the joinings are well closed with this fat lute, the whole is to be covered with slips of linen, spread with lute of lime and whites of eggs. These slips are to be bound round with pack-thread. The second lute is necessary to keep on the fat lute, be¬cause this latter remains soft, and does not become solid enougfr to stick on alone.