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grate, being constructed as in any other furnace. It will be easily understood by considering the section represented in fig. S.

The base, represented by the dotted line ABC, and the top, KLM, are oval plates of iron, the longer diameter, A C, being to the shorter as three to two nearly. The base and top are equal, so that the sides, KA, MC, are upright, the whole body forming an oval cylinder. DE F, is half of the hole in the bottom, which is occupied by the grate fixed on the top of the ash-pit. GHI is half of the mouth of the furnace, which receives a still, or a sand-pot, for distillation, with a retort. This is a little nearer to the front, K, of the top, than the grate-hole is to the front, A, of the bottom, so that the luting is thicker below than above. Near the back, M, of the furnace is a smaller hole, P, for the vent. The luting at Q and R is so formed that the cavity of the furnace does not greatly differ from a cylinder, except in so far as the vent, PO, does not communicate with it abruptly, but is gradually curved downwards, as represented in the figure, making the middle of the cavity more roomy backwards, by which means it contains a greater quantity of fuel. S is the section of the luting, which forms a sort of an arch, or bridge, contracting the entry of the vent. An iron pipe is set on at P to increase the draught of the chimney. The fuel is put into the furnace by the aperture P, and the sloping form of the cavity causes it to distribute itself pretty uniformly.

When the furnace is used for smelting, the crucible is set on a pedestal standing on the grate, and the fuel is placed round it with great ease, the mouth of the furnace being open. This is then shut up by a stopper made on purpose, or by a flat fire. tile simply laid on it.

When we would distil with a naked fire, the retort has its bulb resting on a ring which hangs on the mouth of the furnace by three hooks, and the neck of the retort lies over the front of the furnace. The space round the retort, at the mouth of the furnace is closed, as much as is necessary, by two or three pieces of tile, shaped so as nearly to fit the bulb of the retort when they are laid on the mouth of the furnace. A quantity of light ashes are now to be laid on these tiles, and heaped up so as to cover the bulb and part of the neck of the retort. Dr. Black found that this produced a very gradual diminution of the heat, as it recedes from the fuel, and is less liable to crack the

retort, by inequality of heat, than any other contrivance. Scarcely any process occurs which this furnace does not answer with great ease.

In using the furnaces most convenient for experimental chemistry, (namely, those made of plate iron) it is necessary that the iron be defended from the heat by lining or lute, as we call it, on the inside; and such lutes are necessary in other occasions in chemistry; as when we have occasion to close the joining of the vessels with one another, or to give a coating to retorts, or even to crucibles, which is sometimes done. The materials employed for these purposes have their general denomination from clay, of which some of the most useful are partly composed, though there are some that do not contain any of it. They may be divided into such as contain animal or vegetable matter, of the glutinous or adhesive kind, and such as are composed only of earthy substances. The first are used for closing the joining of vessels, when the heat we mean to apply is not to be strong, nor the vapours to be produced corrosive. The second serve for the lining of furnaces, or for closing the joinings of vessels, in operations in which the vapours are very corrosive, or in which a strong heat must be employed, which would scorch, or burn and destroy, any animal or vegetable glutinous matter.

The joinings of vessels with one another, which we have the most frequent occasion to close up by means of lutes, are those of retorts with receivers. And we may remark, in the first place, with regard to these, that there are not many operations in which it is necessary to make the joining perfectly close, except when the receiver is provided with an air-pipe. On the contrary, it is dangerous on account of the air which must be allowed to escape in some manner. Therefore we are not anxious to contrive the most close and compact. They are sufficient and better if they be moderately so, and in some cases, when we think the lute too close we even obviate it by a pinhole. The animal and vegetable lutes, employed in this way, are glue and chalk mixed in thin paste, and spread on slips of paper; or gum arabic and chalk, used in the same manner; or flour and water; or a bladder; or linseed meal; or fat lute. M. Lavoisier recommends, for joinings which we desire to be air-tight, but which are not to be exposed to heat, the following: to sixteen ounces of bees-wax add

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one and a half or two of turpentine, and keep it for use. When used, soften and make it tough, by warming and working between the fingers; then put it on the joint in little rolls, and make it close; and, lastly, cover it with slips of wet bladder laced with pack-thread. But, if the joint is liable to be warmed, or heated during the operation, you must take fat lute. This is made of raw pipe-clay and linseed oil, beaten together very hard, to the consis. tence of a stiff adhesive paste.

Of the second kind of lutes, called the fire-lutes, a great variety have been proposed, and some of them compositions of many -ingredients, but none are equal, or superior, to clay and sand; viz, sand 3, or 4, or 5, or 6, to clay 1. These are for luting vessels together, and for coatings. But in lining furnaces, Dr. Black used a double lining; first, a charcoal-lute; secondly, a fire-lute.

He found that a layer of powdered charcoal, beaten up, or kneaded, with as little water as will give its particles adhesion enough to attach itself to the metal sides of the furnace, by means of cautious beating, forms a firm stratum, which is the most imperfect conductor of heat of all that he had tried. When this layer of charcoal is defended from the action of the air by a layer of fire-lute, composed of one part of fine clay, and three or four parts of sand, carefully put on, and consolidated by gently beating it from day to day, till it no longer receives an impression from the mallet; it will last as long as any part of the furnace. Its durability will be greatly improved, without much change in its conducting power, by using, instead of pure water, water made muddy by about one-twentieth of pipe-clay. If finely powdered charcoal be kneaded with one-fifth of pipe-clay, it may be kneaded and formed into any shape, and will be so impervious to heat that a bit of it may be held in the fingers within an inch of where it is red hot. Such a composition is, therefore, very proper for the doors of furnaces, and for stopples for such apertures as must be frequently opened and shut.

Fig. 4, represents an Argand's lamp capable of being adjusted at different heights, by a sliding socket, on a stem or rod. Another similar socket is seen above, into which a ring of wire is inserted for supporting the retort, a, at any required distance above the flame. A third socket may be added, still higher upon the stem, for sup

porting another wire, which will afford the means of steadying an alembic, or any other apparatus, by a string or small flexible wire answering the same purpose. This is a very convenient method of disposing vessels for the lamp heat, upon a small or moderate scale, for distillations, sublimation, evaporation, drying, and the like. A small sandbath may be placed, when needful, in the wire above the flame: b is an intermediate condensing vessel, called a quilled receiver, which conveys the condensed product into a bottle, c. The rod which supports b shows how useful these instruments are in their various applications.

The condensation of vapours after distillation, and the transmission of gases, which may arise along with them to their receptacles, has been very well and scientifically effected by the late Mr. Woulfe, in an apparatus of bottles which is distinguished by his name. The original contrivance will be easily understood by description, and instead of a drawing of that arrangement of vessels, we shall give one of the most simple, safe, and convenient of all the improvements which have since been made in it; namely, that contrived by Dr. Hamilton, and figured at the end of his "Translation of Berthollet on Dying." Suppose the retort and receiver, (fig. 1.) or any other distillatory apparatus, to have a communication from the upper parts of the receiver, a, at c by a tube leading into a bottle having three necks, and partly filled with water, beneath the surface of which the said tube, after passing this, an air-tight cork was plunged. Another of the necks of the bottle is provided with an upright open tube, also passing a cork and plunged in the water in order that air may enter in case of absorption, or the liquid may rise a little in it, in case of pressure from within. The third neck of the bottle affords a communication by means of a tube with another two necked bottle, fitted up in all respects in the same manner as the bottle communicating with e. And in this manner we may conceive a series of three or more bottles, the last of which may communicate with a pneumatic apparatus which is to receive the incondensable gas. This system of bottles and tubes is sometimes fitted together by grinding, and sometimes made secure by lutes; but in most constructions, though the advantages are very considerable, the apparatus is difficult to be put together, and easily deranged or injured.

Fig. 5, represents Dr. Hamilton's appa

ratus. A is the retort fitted by grinding into a plug or piece, B, represented at b, which last is also fitted by grinding into the neck of a globular receiver, C.

The use of the additional piece, b, is to afford a due inclination to the retort by an obliquity of its perforation or hole, instead of allowing it to remain horizontal, as it would, if fitted to the hole in C, and also to facilitate the grinding in, of a new retort in the case of breakage. The piece, b, has a stopper, a, which can be put when ever the retort is taken out, whether for weighing at, or for any other purpose. The first receiver, C, has a smaller neck opposite to B, which is ground into a corresponding neck of D, the second receiver, which last is tubulated, and has a tube, H, open at both ends, ground into its vertical neck for the purpose of permitting absorption and re-acting, by its contents, against the force required to protrude any gas through the bended tube, I K L. Every one of the range of the receiver, E FG, has also two necks, by which they are successively fitted to each other, and each interior neck has a tube of about a quarter of an inch fitted into it, which, by its curvate, reaches nearly to the bottom of the liquid (usually water) placed in each. By this disposition the usual first product of condensation is received in C, and the purer vapours proceeding to D, are in part condensed by the water placed therein, and are partly urged through the tube, I, into contact with the water in E: and what ever may escape condensation in E, will be urged through the tube, K, into the liquid in F; and in this manner the operation may proceed through the whole set of yessels, till the gasiform remaining product, if any, shall pass out then beneath the mouth of one or the other of the three inverted bottles, at P, which are filled with water, and have their mouths immersed below the surface of the water, in a dish at the end of the series. S and s are a pair of pieces of wood which serve to support one of the globes, and very conveniently afford an adjustment, by pressing them more or less near together. This apparatus is drawn upon a scale of about half an inch to a foot, which is a proper size to be worked by an Argand's lamp; if it were made larger, the retort would of course require to be supported as usual, by the parts of the furnace, or otherwise.

uently elastic fluids are received and managed. For such gases as are not absorbed by water, a wooden tub may be used, having a shelf therein, at such a depth as to stand a little below the intended surface of the water; or, instead of a shelf, a shortlegged stool, loaded with lead, may be used, and in that case any tub or vessel may be used. Jars, or vessels of any convenient figure, being filled with water by immersion, and turning them bottom upwards, may be placed on the shelf, which should have holes in it for the convenience of pouring up any gas, whether from another jar, bottle, or vessel, or from the neck or tube of a retort, or other apparatus. Jars, &c. thus filled may be conveyed away, either by corking the bottle, or by putting a saucer, or other shallow vessel, beneath the mouth of the jar, and taking both out together, with water in the saucer.

Gases which are absorbed by water are usually received over mercury, in which case, on account of the weight, as well as the expence of the fluid, the vessels are made smaller, and the trough has a deep cavity sufficient for immersion, but no larger, and a broad shallow part of the trough supplies the place of a shelf for the jars to stand upon; and there is an actual shelf at one part only over the end of the deep cavity. Fig. 6, represents a trough for mercury, which may be made of wood or of stone. The space, V, admits the jar, A, to be immersed, and when full it is raised and placed bottom downwards upon the shallow bottom. G is a retort, containing some materials from which gas, being extricated, rises beneath A, and displaces the mercury. X and Y are grooves, into which one or more wooden shelves may be slided, as occasion may require, in which application they are first introduced at the wider part, T, in the plan, fig. 7.

An apparatus, almost indispensable in experiments on the gases, is a gazometer, which enables the operator to receive and preserve large quantities of gas with the aid of only a few pounds of water. These vessels are made of various forms, but one of the most simple is shown in fig. 8. It consists of an outer fixed vessel, d, and an inner moveable one, c, both of japanned iron. The latter slides easily up and down within the other, and is suspended by cords passing pullies, to which are attached the counterpoises, &c. To avoid the incumbrance The dish and bottles at the extremity of, of a great weight of water, the outer vessel, this apparatus show how the gases or perma d, is made double, or is composed of two

1

cylinders, the inner of which is closed at the top and at the bottom. The space only of about half an inch is left between the two cylinders as shown by the dotted lines. In this space the vessel, c, may move freely up and down. The interval is filled with water as high as the top of the inner cylinder. The cup or rim on the top of the outer vessel, is to prevent the water from overflowing when the vessel, c, is forcibly pressed down, in which situation it is placed whenever gas is about to be collected. The gas enters from the vessel in which it is produced; by the communicating opening b, and passes along the perpendicular pipe marked by dotted lines in the centre, into the cavity of the vessel, c, which continues rising till it is full.

To transfer the gas, or to apply it to any purpose, the cock, b, is to be shut, and an empty bladder, or bottle of elastic gum, furnished with a stop cock, is to be screwed on a. When the vessel, c, is pressed down by the hand, the gas passes down the central pipe, which it had before ascended, and its escape at b being prevented, it finds its way up a pipe which is fixed on the outer surface of the vessel, and which is terminated by the cock a. By means of an ivory mouth-piece screwed on this cock, the gas included in the instrument may be respired; the nostrils being closed by the fingers. When it is required to transfer the gas into glass jars standing in water, a crooked tube may be employed, one end of which is screwed upon the cock, b, while the other aperture is brought under the inverted funnel, fixed into the shelf of the pneumatic trongh.

Several alterations have been made in the form of this apparatus, but they are principally such as add merely to its neatness and beauty, and not to its utility; and they render it less easy of explanation. The counterpoises, e e, are now generally concealed in the framing, and the vessel c is frequently made of glass.

When large quantities of gas are required (as at a public lecture) the gas holder, fig. 9, will be found extremely useful. It is made of tinned iron plate, japanned both within and without. Two short pipes a, and c, terminated by cocks, proceed from its sides, and another, b, passes through the middle of the top or cover, to which it is soldered, and reaches within half an inch of the bottom.

It will be found convenient also to have an air cock with a very wide bore fixed to

the funnel at b. When gas is to be transferred into this vessel from the gazometer, the vessel is first completely filled with water through the funnel, the cock a being left open and c shut. By means of an horizontal pipe, the aperture a is connected with a of the gazometer. The cock b being shut, a and c are opened, and the vessel c of the gazometer, fig. 8, gently pressed downwards with the hand. The gas then descends from the gazometer till the air-holder is full, which may be known by the water ceasing to escape through the cock c. All the cocks are then to be shut, and the vessels disunited. To apply this gas to any purpose, an empty bladder may be screwed on a; and water being poured through the funnel b, a corresponding quantity of gas is forced into the bladder. By lengthening the pipe, b, the pressure of a column of water may be added; and the gas being forced through a, with considerable velocity, may be applied to the purpose of a blowpipe, &c. &c.

The gazometer already described, is fitted only for the reception of gases that are confinable by water, because quicksilver would act on the tinning and solder of the vessel, and would not only be spoiled itself, but would destroy the apparatus. Yet an instrument of this kind, in which mercury can be employed, is peculiarly desirable, on account of the great weight of that fluid; and two varieties of the mercurial gazometer have therefore been invented. The one of glass, is the contrivance of Mr. Clayfield, and may be seen represented in the plate prefixed to Mr. Davy's researches. In the other, invented by Mr. Pepys the cistern for the mercury is of cast iron. A drawing and representation of it may be found in the fifth volume of the Philosophical Magazine; but as neither of these instruments are essential to the chemical student, and as they are required only in experiments of research, we refer to the minute descriptions of their respective inventors.

Very complete sketches of chemical instruments and furnaces may be seen in Henry's chemistry.

After the general description we have here given of the arrangement and apparatus for chemical experiments, we shall conclude with a short account of the blow-pipe.

It is a tube which terminates in a perforation not exceeding the hole which might be made by a small pin. There is no difficulty, in case of emergency, in making one

LABORATORY.

ont of a tube of glass, and the common
blow-pipes sold at the ironmongers for a few
pence, and in universal use with workmen
are very good. Others more costly and
elegant, which have a small space for the
condensation of the vapour of the breath,
are sold by the makers of chemical appara-
tus. It requires some address to produce
a constant stream of air by blowing through
this pipe; but the principal artifice con.
sists in keeping the tongue to the roof of the
mouth, and using the breath by the pressure
of the muscles of the face instead of the
chest. Some workmen in glass contrive to
hold the pipe steady between the teeth,
and by that means have both hands at li
berty for use; but as this requires uncom-
mon steadiness in the head, the philosophi-
cal chemist will probably prefer fixing his
pipe to one of his stands. Some blow-pipes
have been made, through which a stream of
vapour from boiling alcohol is urged; but
these instruments seem to be rather toys
than of use to the actual chemical investi-
gator. It appears preferable to use bel-
lows, as the enamellers do, where an ex-
tensive application of this implement is re-
quired; though in this case the desirable
requisite of portability is lost sight of.

The bodies intended to be heated by the
blow-pipe must not, in general, exceed the
size of a pepper-corn, unless bellows and a
very large flame be used. The proper sup-
ports are either a piece of smooth, close
grained charcoal, for such bodies as are not
subject to an alteration of their properties,
from the inflammability of the coal, as
might be contrary to the nature of the in-
vestigation. This support is therefore most
frequently used; as it is properly adapted
for saline, earthy, and many metallic bò
dies. The other support consists of a spoon,
somewhat less than a quarter of an inch in
diameter, male of a metal not subject to
oxydation; that is to say, pure gold, silver,
or platina, or such a mixture of these me-
tals as might be found to be least deficient
in the requisite degree of hardness, which
gold or silver alone does not possess.. Berg-
man advised to add one-tenth of platina to
a given mass of silver. There is, however,
no very considerable inconvenience result-
ing from the use of a small spoon, either of
gold or of silver; and platina possesses
every quality which can be wished for.
The small metallic spoon must of course be
properly fixed in a socket of metal, pro-
vided with a wooden handle.

Very small or pulverulent substances are

apt to be carried away by the current of
small hole in the charcoal, into which the
flame. These may be secured by making a
powder is to be put, and covered with ano-
ther small piece of charcoal, which partly
ments of reduction are made by binding
protects them from the flame. Some experi
ting a channel along the piece intended to
two small pieces of charcoal together, cut-
be the undermost, and making a cavity in
the middle of this channel to contain the
subject matter of examination. With this
channel between the two pieces of coal,
apparatus the flame is urged through the
and violently heats the substance in the ca
vessel.
vity, which may be considered as a closed

A great number of mineral bodies are
not fusible by mere flame, urged by com-
mon air through the blow-pipe; though oxy-
gen gas subdues most bodies. See GAS
oxygen.

Whenever, therefore, the fusion of any some other substance must be added which refractory substance is to be attempted, is more fusible, and capable of dissolving the former. These solvents, in the dry way, are distinguished by the name of fluxes, and, like the solvents used in the humid way, are mostly saline. It may easily be will greatly vary, according to that of the imagined, that the nature of the products flux, which enters into combination with them; and accordingly they are varied in experiments, as well as in operations, in the though conducted upon the same principles large way. The blow-pipe experiments, as those upon a larger scale, differ nevertheless from them in two particulars; namely, that the whole of the phenomena are visible throughout, and that the residues are indicate facts. For these reasons, every of no value, otherwise than as they serve to flux, without exception, might be used with a nature as to sink into the charcoal. We the blow-pipe, provided it were not of such may therefore select a certain small number of the most convenient fluxes, and note the effects which they respectively produce upon the various mineral bodies; and these will serve as indications to enable the chemical enquirer to distinguish them again with a great degree of accuracy, not to mention, that he may also derive much advantage, with regard to the more extensive operations he might be disposed to undernary labour has already been performed by take. A considerable part of this prelimiEngestrom, Bergman, Mongez, and others;

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