When the furnace is filled with coals and kindled, if the door of the ash-hole be set wide open, and that of the fire-place shut very close, the force of the fire is increased; and if, moreover, the pyramidal cover be put on the top, and the conical funnel added to it, the fire will become still more fierce.

Seeing the matters contained in this furnace are encompassed with fire on all sides, except in the fore-part opposite to the door of the fire-place, and as there are occasions which require that the force of the fire should be applied to this part also, an iron box, of the shape and size of the door, hath been contrived to answer that purpose. This box is filled with lighted coals, and applied immediately to the door-place, by which means the heat there is considerably augmented. This help may be made use of at the beginning of the operation, in order to accelerate it, and bring the heat sooner to the desired degree; or in case a very fierce heat be required; or at a time when the air being hot and moist will not make the fire burn with the necessary vigour.

The heat may be lessened by removing the iron box, and shutting the door of the fire-place quite close. It may be still further and gradually diminished, by taking off the conical funnel from the top; by shutting the door of the fire-place with one of its plates only, that which has the least, or that which has the greatest aperture in it; by taking off the pyramidal cover; by shutting the ash-hole door wholly or in part; and, lastly, by setting the door of the fire-place wide open: but, in this last case, the cold air penetrates into the cavity of the Muffle, and refrigerates the cupels more than is almost ever necessary. If it be observed, during the operation, that the Muffle grows cold in any particular part, it is a sign there is a vacuity left by the coals in that place: in this case an iron wire must be thrust into the furnace, through the hole which is over the door of the fire-place, and the coals stirred therewith, so as to make them fall into their places and fill up the vacant interstices.

It is proper to observe, that, besides what has been said concerning the ways of increasing the activity of the fire in the cupelling furnace, several other causes also may concur to procure to the matters contained in the Muffle a greater degree of heat: for example, the smaller the Muffle is, the wider and more numerous the holes in it are; the nearer to its bottom, or further end, the cupels are placed, the more will the matters therein contained be affected with heat.

Besides the operations to be performed by the cupel, this furnace is very useful, and even necessary, for many chymical experiments; such, for instance, as those relating to sundry vitrifications and enamelling. As it is pretty low, the best way is to place it, when it is to be used, on a base of brick-work that may raise it to a level with the operator's hand.

A Lamp-furnace is exceeding useful for all operations that require only a moderate, but long-continued, degree of heat. The furnace for working with a lamp-heat is very simple: it consists only of a hollow cylinder, from fifteen to eighteen inches high, and five or six in diameter, having at its bottom an aperture large enough for a lamp to be introduced and withdrawn with ease. The lamp must have three or four wicks, to the end that by lighting more or fewer of them a greater or less degree of heat may be produced. The body of the furnace must moreover have several small holes in it, in order to supply the flame of the lamp with air enough to keep it alive.

On the top of this furnace stands a bason five or six inches deep, which ought to fill the cavity of the cylinder exactly, and to be supported at its circumference by a rim which may entirely cover and close the furnace: the use of this bason is to contain the sand through which the lamp-heat is usually conveyed.

Besides this, there must be a kind of cover or dome made of the same material with the furnace, and of the same diameter with the sand-bath, without any other opening than a hole, nearly circular, cut in its lower extremity. This dome is a sort of reverberatory, which serves to confine the heat and direct it towards the body of the retort; for it is used only when something is to be distilled in a vessel of this fashion; and then the hole at its bottom serves for a passage to the neck of the retort. This dome should have an ear or handle, for the conveniency of putting it on and taking it off with ease.

Of Lutes.

If the vapours are more acrid, or more spirituous, recourse may be had to slips of bladder long steeped in water, which containing a sort of natural glue, close the junctures of the vessels very well.

If it be required to confine vapours of a still more penetrating nature, it will be proper to employ a lute that quickly grows very hard; particularly a paste made with quick-lime and any sort of jelly, whether vegetable or animal; such as the white of an egg, stiff size, &c. This is an excellent lute, and not easily penetrated. It is also used to stop any cracks or fractures that happen to glass vessels. But it is not capable of resisting the vapours of mineral acid spirits, especially when they are strong and smoking: for that purpose it is necessary to incorporate the other ingredients thoroughly with fat earth softened with water; and even then it frequently happens that this lute is penetrated by acid vapours, especially those of the spirit of salt, which of all others are confined with the greatest difficulty.

In such cases its place may be supplied with another, which is called Fat Lute, because it is actually worked up with fat liquors. This lute is composed of a very fine cretaceous earth, called tobacco-pipe clay, moistened with equal parts of the drying oil of lint-seed, and a varnish made of amber and gum copal. It must have the consistence of a stiff paste. When the joints of the vessels are closed up with this lute, they may, for greater security, be covered over with slips of linen smeared with the lute made of quick-lime and the white of an egg.

Chymical vessels are liable to be broken in an operation by other causes besides the sudden application of heat or cold. It frequently happens, that the vapours of the matters exposed to the action of fire rush out with such impetuosity, and are so elastic, that, finding no passage through the lute with which the joints of the vessels are closed, they burst the vessels themselves, sometimes with explosion and danger to the operator.

To prevent this inconvenience, it is necessary that in every receiver there be a small hole, which being stopped only with a little lute may easily be opened and shut again as occasion requires. It serves for a vent-hole to let out the vapours, when the receiver begins to be too much crowded with them. Nothing but practice can teach the artist when it is requisite to open this vent. If he hits the proper time, the vapours commonly rush out with rapidity, and a considerable hissing noise; and the vent should be stopped again as soon as the hissing begins to grow faint. The lute employed to stop this small hole ought always to be kept so ductile, that, by taking the figure of the hole exactly, it may entirely stop it. Besides, if it should harden upon the glass, it would stick so fast that it would be very difficult to remove it without breaking the vessel. This danger is easily avoided by making use of the fat lute, which continues pliant for a long time, when it is not exposed to an excessive heat.

This way of stopping the vent-hole of the receiver has yet another advantage: for if the hole be of a proper width, as a line and half, or two lines, in diameter, then, when the vapours are accumulated in too great a quantity, and begin to make a great effort against the sides of the receiver, they push up the stopple, force it out, and make their way through the vent-hole: so that, by this means, the breaking of the vessels may always be certainly prevented. But great care must be taken that the vapours be not suffered to escape in this manner, except when absolute necessity requires it; for it is generally the very strongest and most subtile part of a liquor which is thus dissipated and lost.

Heat being the chief cause that puts the elasticity of the vapours in action, and prevents their condensing into a liquor, it is of great consequence in distillation that the receiver be kept as cool as possible. With this view a thick plank should be placed between the receiver and the body of the furnace, to intercept the heat of the latter, and prevent its reaching the former. As the vapours themselves rise very hot from the distilling vessel, they soon communicate their heat to the receiver, and especially to its upper part, against which they strike first. For this reason it is proper that linen cloths, dipt in very cold water, be laid over the receiver, and frequently shifted. By this means the vapours will be considerably cooled, their elasticity weakened, and their condensation promoted.

By what hath been said in this first part, concerning the properties of the principal agents in Chymistry, the construction of the most necessary vessels and furnaces, and the manner of using them, we are sufficiently prepared for proceeding directly to the operations, without being obliged to make frequent and long stops, in order to give the necessary explanations on those heads.

Nevertheless, we shall take every proper occasion to extend the theory here laid down, and to improve it by the addition of several particulars, which will find their places in our Treatise of Chymical Operations.

ELEMENTS
OF THE
PRACTICE of CHYMISTRY;

WHEREIN

The Fundamental Operations are described, and illustrated by Observations on each Process.

ELEMENTS
OF THE
PRACTICE OF CHYMISTRY.

INTRODUCTION.

As the Elements of the Theory of Chymistry, delivered in the former part of this work, were intended for the use of persons supposed to be altogether unacquainted with the art, they could not properly admit of any thing more than fundamental principles, so disposed as constantly to lead from the simple to the compound, from things known to things unknown: for which reason I could not therein observe the usual order of Chymical Decomposition, which is not susceptible of such a method. I therefore supposed all the analyses made, and bodies reduced to their simplest principles; to the end that, by observing the chief properties of those primary elements, we might be enabled to trace them through their several combinations, and to form some sort of judgment a priori of the qualities of such compounds as may result from their junctions.

But this latter part is of a different nature. It is a practical Treatise, intended to contain the manner of performing the principal Operations of Chymistry; the operations which serve as standards for regulating all the rest, and which confirm the fundamental truths laid down in the Theory.

As these operations consist almost wholly of analyses and decompositions, there can be no doubt concerning the order proper to be observed in giving an account of them: it evidently coincides with that of the analysis itself.

But as all bodies, which are the subjects of Chymical operations, are divided by nature into three classes or kingdoms, the mineral, the vegetable, and the animal, the analysis thereof may naturally be divided into three branches: some difference may also arise from the different order in which these three may be treated of.

As the reasons assigned for beginning with one kingdom rather than with another have never been thoroughly canvassed, and may perhaps seem equally good when viewed in a particular light, Chymical writers differ in their opinions on this point. For my part, without entering into a discussion of the motives which have determined others to follow a different order, I shall only produce the reasons that led me to begin with the mineral kingdom, to examine the vegetable in the second place, and to conclude with the animal.

First, then, seeing vegetables draw their nourishment from minerals, and animals derive theirs from vegetables, the bodies which constitute these three kingdoms seem to be generated the one by the other, in a manner that determines their natural rank.

Secondly, this disposition procures us the advantage of tracing the principles, from their source in the mineral kingdom, down to the last combinations into which they are capable of entering, that is, into animal matters; and of observing the successive alterations they undergo in passing out of one kingdom into another.

Thirdly and lastly, I look upon the analysis of minerals to be the easiest of all; not only because they consist of fewer principles than vegetables and animals, but also because almost all of them are capable of enduring the most violent action of fire, when that is necessary to their decomposition, without any considerable change or diminution of their principles, to which those of other substances are frequently liable.

Besides, I am not singular in this distribution of the three classes of bodies, which are the subjects of the chymical analysis: as it is the most natural, it has been adopted by several authors, or rather by most who have published Treatises of Chymistry. But there is something peculiarly my own in the manner wherein I have treated the analysis of each kingdom. In the mineral kingdom, for instance, will be found a considerable number of operations not to be met with in other Treatises of Chymistry; the authors having probably considered them as useless, or in some measure foreign, to the purpose of Elementary Books, and as constituting together a distinct art. I mean the processes for extracting saline and metallic substances from the minerals containing them.

Yet, if it be considered that salts, metals, and semi-metals are far from being produced by nature in a state of perfection, or in that degree of purity which they are commonly supposed to have when they are first treated of in Books of Chymistry; but that, on the contrary, these substances are originally blended with each other, and adulterated with mixtures of heterogeneous matters, wherewith they form compound minerals; I imagine it will be allowed, that the operations by which these minerals are decomposed, in order to extract the metals, semi-metals, and other simpler substances, especially as they are founded on the most curious properties of these substances, are so far from being useless or foreign to the purposes of an Elementary Treatise, that they are, on the contrary, absolutely necessary thereto.

After I had made these reflections, I could not help thinking that an analysis of minerals, which should treat of saline and metallic substances, without taking any notice of the manner in which their matrices must be analysed, in order to extract them, would be no less defective than a treatise of the analysis of vegetables, in which Oils, essential Salts, fixed and volatile Alkalis, should be amply treated of, without saying one word of the manner of analysing the plants from which these several substances are obtained. I therefore thought myself indispensably obliged to describe the manner of decomposing every ore or mineral, before I attempted to treat of the saline or metallic substance which it yields.

For example: as the Vitriolic Acid, with the consideration of which I begin my Mineral Analysis, is originally contained in Vitriol, Sulphur, and Alum; and as these substances again derive their origin from the sulphureous and ferruginous Pyrites, the first operations I describe under this head are the processes for decomposing the Pyrites in order to extract its Vitriol, Sulphur, and Alum. I then proceed to the particular analysis of each of these substances, with a view to extract their Vitriolic Acid; and afterwards deliver, in their order, the other operations usually performed on this Acid. Thus it appears, that this saline substance occasions my describing the analyses of the Pyrites, Vitriol, Sulphur, and Alum. The whole of the Treatise on Minerals proceeds on the same plan.

The operations by which we decompose ores and minerals are of two sorts: those employed in working by the great, and those for trying in small the yield of any ore. These two manners of operating are sometimes a little different; yet in the main they are the same, because they are founded on the same principles, and produce the same effects.

As my chief design was to describe the operations that may be conveniently performed in a laboratory, I have preferred the processes for small assays: especially as they are usually performed with more care and accuracy than the operations in great works: and here I must acknowledge, that I am obliged to M. Cramer's Docimasia, or Art of Assaying, for all the operations of this kind in my analysis of minerals. As M. Hellot's work on that subject did not appear till after I had finished this, M. Cramer's Docimasia, in which sound Theory is joined with accurate practice, was the best book of the kind I could at that time consult. I therefore preferred it to all others; and as I have not quoted it in my analysis of minerals, because the quotations would have been too frequent, let what I say here serve for a general quotation. I have been careful to name, as often as occasion required, the other authors whose processes I have borrowed: it is a tribute justly due to those who have communicated their discoveries to the public.

Though I have told the reader that in my analysis of minerals he will find the processes for extracting out of each the saline or metallic substances contained in it, yet he must not expect that this book will instruct him in all that is necessary he should know to be able to determine, by an accurate assay, the contents of every mineral. My intention was not to compose a Treatise of Assaying; and I have taken in no more than was absolutely necessary to make the analysis of minerals perfectly understood, and to render it as complete as it ought to be in an Elementary Treatise. I have therefore described only the principal operations relating thereto; the operations which are fundamental, and which, as I said before, are to serve as standards for the rest, abstracted from such additional circumstances as are of consequence only to the Art of Assaying, properly so called.

Such therefore as are desirous of being fully instructed in that Art, must have recourse to those works which treat professedly of the subject; and particularly to that published by M. Hellot: a performance most esteemed by such as are best skilled in Chymistry, and rendered so complete by the numerous and valuable observations and discoveries of the Author, that nothing better of the kind can be wished for. I thought it proper to give these notices in relation to my analysis of minerals; and shall now proceed to shew the plan of my analyses of vegetables and of animals.

Seeing all vegetable matters are susceptible of fermentation, and when analysed after fermentation, yield principles different from those we obtain from them before they are fermented, I have divided them into two classes; the former including vegetables in their natural state, before they have undergone fermentation; and the latter those only which have been fermented. This analysis opens with the processes by which we extract from vegetables all the principles they will yield without the help of fire: and then follow the operations for decomposing plants by degrees of heat, from the gentlest to the most violent, both in close vessels, and in the open air.

I have not made the same division in the animal kingdom, because the substances that compose it are susceptible only of the last degree of fermentation, or putrefaction; and moreover the principles they yield, whether putrefied or unputrefied, are the very same, and differ only with regard to their proportions, and the order in which they are extricated during the analysis.

I begin this analysis with an examination of the milk of animals that feed wholly on vegetables; because, though this substance be elaborated in the body of the animal, and by that means brought nearer to the nature of animal matters, yet it still retains a great similitude to the vegetables from which it derives its origin, and is a sort of intermediate substance between the vegetable and animal. Then I proceed to the analysis of animal matters properly so called, those which actually make a part of the animal body. I next examine the excrementitious substances, that are thrown out of the animal body as superfluous and useless. And then I conclude this latter part with operations on the Volatile Alkali; a saline substance of principal consideration in the decomposition of animal matters.

Though, in the general view here given of the order observed in this Treatise of Practical Chymistry, I have mentioned only such processes as serve for analysing bodies, yet I have also inserted some other operations of different kinds. The book would be very defective if it contained no more: for the design of Chymistry is not only to analyse the mixts produced by nature, in order to obtain the simplest substances of which they are composed, but moreover to discover by sundry experiments the properties of those elementary principles, and to recombine them in various manners, either with each other, or with different bodies, so as to reproduce the original mixts with all their properties, or even form new compounds which never existed in nature. In this book therefore the reader will find processes for combining and recompounding, as well as for resolving and decomposing bodies. I have placed them next to the processes for decomposition, taking all possible care not to interrupt their order, or break the connection between them.

PART I.
Of MINERALS.

SECTION I.

Operations performed on Saline Mineral Substances.

CHAP. I.

Of the Vitriolic Acid.

PROCESS I.

Put all these waters together into a glass vessel that widens upwards; set it on a sand-bath, and heat the liquor till a considerable smoke arises; but take care not to make it boil. Continue the same degree of fire till the surface of the liquor begins to look dim, as if some dust had fallen into it; then cease evaporating, and remove the vessel into a cool place: in the space of four and twenty hours will be formed therein a quantity of crystals, of a green colour and a rhomboidal figure: these are Vitriol of Mars, or Copperas. Decant the remaining liquor; add thereto twice its weight of water; filter, evaporate, and crystallize as before; repeat these operations till the liquor will yield no more crystals, and keep by themselves the crystals obtained at each crystallization.

OBSERVATIONS.

The Pyrites are minerals which, by their weight and shining colours, frequently impose on such as are not well acquainted with ores. At first sight they may be taken for very rich ones; and yet they consist only of a small quantity of metal combined with much sulphur or arsenic, and sometimes with both.

They strike fire with a steel as flints do, and emit a sulphureous smell: so that they may be known by this extemporaneous proof. The metal most commonly and most abundantly found in the Pyrites is iron; the quantity whereof sometimes equals, or even exceeds, that of the sulphur. Besides metallic and sulphureous matters, the Pyrites contain also some unmetallic earth.

There are several sorts of Pyrites: some of them contain only iron and arsenic. They have not all the property of efflorescing spontaneously in the air, and turning into vitriol: none do so but such as consist only of iron and sulphur, or at least contain but a very small portion of copper, or of arsenic: and even amongst those that are composed of iron and sulphur alone, there are some that will continue for years together exposed to the air without shooting, and indeed without suffering the least sensible alteration.

The efflorescence of the Iron Pyrites, and the changes they undergo, are phenomena well worth our notice. They depend on the singular property which iron possesses of decomposing sulphur by the help of moisture. If very fine iron-filings be accurately mingled with flowers of sulphur, this mixture, being moistened with water, grows very hot, swells up, emits sulphureous vapours, and even takes fire; what remains is found converted into Vitriol of Mars. On this occasion, therefore, the sulphur is decomposed; its inflammable part is dissipated or consumed; its acid combines with the iron, and a Vitriol arises from that conjunction.

This is the very case with the Pyrites that consist only of iron and sulphur; yet some of them, as we said before, do not effloresce spontaneously and turn to Vitriol. The reason probably is, that, in such minerals, the particles of iron and sulphur are not intimately mixed together, but separated by some earthy particles.

In order to procure Vitriol from Pyrites of this kind, they must be for some time exposed to the action of fire, which, by consuming part of their sulphur, and rendering their texture less compact, makes way for the air and moisture, to which they must be afterwards exposed, to penetrate their substance, and produce in them the changes with which those others are affected that germinate spontaneously.

The Pyrites which contain copper and arsenic, and for that reason do not effloresce, must likewise undergo the action of fire; which, besides the effects it produces on Pyrites that consist of iron and sulphur only, dissipates also the greatest part of the arsenic. These Pyrites being first roasted, and then exposed to the air for a year or two, do also yield Vitriol; but then it is not a pure Vitriol of Iron, but is combined with a portion of blue Vitriol, the basis of which is Copper.

Sometimes also there is Alum in the vitriolic waters drawn off the Pyrites. It was on account of this mixture of different salts that we recommended the keeping apart the crystals obtained from each different crystallization: for by this means they may be examined separately, and the species to which they belong discovered.

When Vitriol of Iron is adulterated with a mixture of the Vitriol of Copper only, it is easy to purify it and bring it to be entirely martial, by dissolving it in water, and setting plates of iron in the solution: for iron having a greater affinity than copper with the vitriolic acid, separates the latter from it, and assuming its place produces a pure Vitriol of Mars.

In large works for extracting Vitriol from the Pyrites they proceed thus. They collect a great quantity of Pyrites on a piece of ground exposed to the air, and pile them up in heaps of about three feet high. There they leave them exposed to the action of the air, sun, and rain, for three years together; taking care to turn them every six months, in order to facilitate the efflorescence of those which at first lay undermost. The rain-water which has washed those Pyrites is conveyed by proper channels into a cistern; and when a sufficient quantity thereof is gathered, they evaporate it to a pellicle in large leaden boilers, having first put into it a quantity of iron, some part of which is dissolved by the liquor, because it contains a vitriolic acid that is not fully saturated therewith. When it is sufficiently evaporated, they draw it off into large leaden or wooden coolers, and there leave it to shoot into crystals. In these last vessels several sticks are placed, crossing each other in all manner of directions, in order to multiply the surfaces on which the crystals may fasten.

The Pyrites are not the only minerals from which Vitriol may be procured. All the ores of iron and copper that contain sulphur may also be made to yield green or blue Vitriol, according to the nature of each, by torrefying them, and leaving them long exposed to the air: but this use is seldom made of them, as there is more profit to be got by extracting the metals they contain. Besides, it is easier to obtain Vitriol from the Pyrites than from those other mineral substances.

PROCESS II.

Of all minerals the Pyrites contain the most Sulphur; those especially which have the colour of fine brass, a regular form, such as round, cubical, hexagonal, and being broken present a number of shining needles, all radiating, as it were, from a center.

A very moderate heat is sufficient to separate the Sulphur they contain. We directed that the retort employed should have a long and wide neck, with a view to procure a free passage for the Sulphur: the water set in the receiver detains the Sulphur, fixes it, and prevents it from flying off; so that it is unnecessary to close the joints of the vessels. But it is proper to take notice, that whenever you use an apparatus for distilling, which requires the beak of the retort to be under water, it is of very great consequence that the fire be constantly so regulated, that the retort may not cool in the least; for, in that case, as the rarefied air contained therein would be condensed, the water in the receiver would rise into the retort and break it.

If in distilling Sulphur, according to the present process, the matter contained in the retort should happen to melt, the operation would be thereby considerably protracted, and it would require a great deal more time to extract all the Sulphur; because all evaporation is from the surface only, and the matter, while it remains in a coarse powder, presents a much more extensive surface than when it is melted.

This remark holds with regard to all other distillations. Any quantity of liquor, set to distil in its fluid state, will take much more time to rise in vapours, and pass from the retort into the receiver, than if it be incorporated with some solid body reduced to minute parts, so that the whole shall make a moist powder; and this though the very same degree of fire be applied in both cases.

If the matter from which it is proposed to extract Sulphur be such as will melt with the degree of fire necessary to this operation; that is, with a heat which will make the retort but faintly red, it must be mixed with some substance that is not so fusible. Very pure coarse sand, or clean gravel, may be used with success: but absorbent earths are altogether improper for this purpose, because they will unite with the Sulphur.

The sulphureous minerals which are most apt to fuse are the cupreous Pyrites, or yellow copper ores: common lead ores are also very fusible.

The Pyrites are by this operation deprived of almost all the Sulphur they contain; and consequently little is left behind, but the particles of iron and copper, together with a portion of unmetallic earth, which we shall shew how to separate from these metals, when we come to treat of them. I say that by this operation the Pyrites are deprived of almost all, and not entirely of all their Sulphur; because, this separation being made in close vessels only, there always remains a certain quantity of Sulphur, which adheres so obstinately to the metals, that it would be almost impossible to get it all out, even though a much stronger fire than that directed in the process were applied for this purpose, and though choice had been, as it ought to be, made of such Pyrites, or other sulphureous Minerals as part most easily with their sulphur. Nothing but a very strong fire in the open air is capable of carrying it wholly off, or consuming it entirely.

In several places are found great quantities of native Sulphur. The Volcanoes abound with it, and people gather it at the foot of those burning mountains. Several springs of mineral waters also yield Sulphur, and it is sometimes found sublimed to the vaulted roofs of certain wells, and among others in one at Aix-la-Chapelle.

The Germans and Italians have large works for extracting Sulphur in quantities out of Pyrites, and other minerals which abound therewith. The process they work by is the same with that here delivered; but with this difference only, that Sulphur being but of small value they do not use so many precautions. They content themselves with putting the sulphureous minerals into large crucibles, or rather earthen cucurbits, which they place in the furnace in such a manner that, when the sulphureous part melts, it runs into vessels filled with water, and is thereby fixed.

The Sulphur obtained, either by distillation or by simple fusion, is not always pure.

When it is obtained by distillation, if the matters from which you extract it contain moreover some other minerals of nearly the same volatility, such, for instance, as Arsenic, or Mercury, these minerals will come over with it. This is easily perceived: for pure sublimed Sulphur is always of a beautiful yellow, inclining to a lemon colour. If it look red, or have a reddish cast, it is a sign that some Arsenic hath risen along with it.

Mercury sublimed with Sulphur likewise gives it a red colour; but Sulphur is very seldom adulterated with this metallic substance: for Arsenic is frequently found combined with the Pyrites, and other sulphureous minerals; whereas, on the contrary, we very rarely meet with any Mercury in them.

But if Mercury should happen to rise with the Sulphur in distillation, it may be discovered by examining the sublimate; which, in that case, will have the properties of Cinabar: on being broken its inside will appear to consist of needles adhering laterally to each other; its weight will be very considerable; and, lastly, the great heat of the place where it is collected will furnish another mark to know it by; for, as Cinabar is less volatile than Arsenic or Sulphur, it fastens on places too hot for either Sulphur or Arsenic to bear.

Sulphur may also be adulterated with such fixed matters, either metallic or earthy, as it may have carried up along with it in the distillation, or as may have been sublimed by the Arsenic, which has a still greater power than Sulphur to volatilize fixed bodies.

If you desire to free the Sulphur from most of these heterogeneous matters, it must be put into an earthen cucurbit, and set in a sand-bath. To the cucurbit must be fitted one or more aludels, and such a degree of heat applied as shall but just melt the Sulphur; which is much less than that necessary to separate the Sulphur from its matrix. As soon as the Sulphur is melted it will sublime in lemon-coloured flowers, that will stick to the insides of the aludels.

When nothing more appears to rise with this degree of heat, the vessels must be suffered to cool. At the bottom of the cucurbit will be found a sulphureous mass, containing the greatest part of the adventitious matters that were mixed with the Sulphur, and more or less red or dark-coloured, according to the nature of those matters.

When we come to treat of Arsenic and Mercury, we shall give the methods of separating Sulphur entirely from those metallic substances.

PROCESS III.

When your matters are thus prepared, put them into a leaden or glass vessel; pour upon them thrice their weight of hot water; boil the liquor; filter it; and repeat these operations till the earth be so edulcorated that the water which comes off it hath no taste. Mix all these solutions together, and let them stand four and twenty hours, that the gross and earthy parts may settle to the bottom; or else filter the liquor: then evaporate till it will bear a new-laid egg. Now let it cool, and stand quiet four and twenty hours: in that time some crystals will shoot, which are most commonly vitriolic; for Alum is rarely obtained by the first crystallization. Remove these vitriolic crystals: if any crystals of Alum be found amongst them, these must be dissolved anew, and set to crystallize a second time in order to their purification; because they partake of the nature as well as of the colour of vitriol. By this method extract all the Alum that the liquor will yield.

If you get no crystals of Alum by this means, boil your liquor again, and add to it a twentieth part of its weight of a strong alkaline lixivium, or a third part of its weight of putrefied urine, or a small quantity of quick-lime. Experience and repeated trials must teach you which of these three substances is to be preferred, according to the particular nature of the mineral on which you are to operate. Keep your liquor boiling, and if there be any alum in it, there will appear a white precipitate: in that case let it cool and settle. When the white precipitate is entirely fallen, decant the clear, and leave the crystals of Alum to shoot at leisure, till the liquor will yield no more: it will then be exceeding thick.

OBSERVATIONS.

Alum is obtained from several sorts of Minerals. In some parts of Italy, and in sundry other places, it effloresces naturally on the surface of the earth. There it is swept together with brooms, and thrown into pits full of water. This water is impregnated therewith till it can dissolve no more. Then it is filtered, and set to evaporate in large leaden vessels; and when it is sufficiently evaporated, and ready to shoot into crystals, it is drawn off into wooden coolers, and there left for the salt to crystallize.

In aluminous soils there are often found springs strongly impregnated with Alum: so that to obtain it, the water need only be evaporated.

In the country about Rome there is a very hard stone, which is hewn out of the quarry just like other stones for building; this stone yields a great deal of Alum. In order to extract it, the stones are calcined for twelve or fourteen hours; after which they are exposed to the air in heaps, and carefully watered three or four times a-day for forty days together. In that time they begin to effloresce, and to throw out a reddish matter on their surface. Then they are boiled in water, which dissolves all the Alum they contain, and, being duly evaporated, gives it back in crystals. This is the Alum called Roman Alum.

Several sorts of Pyrites also yield a great deal of Alum. The English have a stone of this kind, which, in colour, is very like a slate. This stone contains much Sulphur, which they get rid of by roasting it. After this they steep the calcined stone in water, which dissolves the Alum it contains, and to this solution they add a certain quantity of a lye made of the ashes of sea-weeds.

The Swedes have a Pyrites of a bright golden colour, variegated with silver spots, from which they procure Sulphur, Vitriol, and Alum. They separate from it the Sulphur and the Vitriol by the methods above prescribed. When the liquor which hath yielded Vitriol is become thick, and no more vitriolic crystals shoot in it, they add an eighth part of its weight of putrefied urine, mixed with a lye made of the ashes of green wood. Upon this there appears and falls to the bottom a copious red sediment. They decant the liquor from this precipitate, and, when it is duly evaporated, find it shoot into beautiful crystals of Alum.

What hath been said, concerning the several matrices from which Alum is obtained, sufficiently shews, that it is seldom solitary in the waters with which aluminous subjects have been lixiviated. It is almost always accompanied with a certain quantity of Vitriol, or other saline mineral matters, which obstruct its crystallization, and prevent its being pure. It is with a view to free it from these matters, that the waters impregnated with Alum are mixed with a certain quantity of the lye of some fixed Alkali, or with putrefied urine, which contains much volatile Alkali. These Alkalis have the property of decompounding all the Neutral salts which have for their basis either an absorbent earth or a metallic substance; and such as have a metallic substance for their basis more readily than those whose basis is an earth. Consequently, if they are mixed with a liquor in which both these sorts of salts are dissolved, they must decompound that sort whose basis is metallic sooner than the other whose basis is an earth. This is what comes to pass in a solution of Alum and Vitriol. The metallic part of the latter is separated from its acid by the Alkalis when mixed with that solution; and it is this metallic part, which is generally iron, that appears in the form of a reddish precipitate, as above-mentioned.

But because Alkalis decompound also those Neutral salts which have an earth for their basis, care must be taken that too much thereof be not added; else what you put in, more than is necessary to decompound the vitriolic salts in your liquor, will attack the Alum, and decompound it likewise.

The Alkali made use of to promote the crystallization of the Alum joins with the Vitriolic Acid, which had dissolved the substances now precipitated, and therewith forms different Neutral salts according to its particular nature. If the Alkali be a lixivium of common wood-ashes, the Neutral salt will be a vitriolated Tartar; if a lixivium of the ashes of a maritime plant like Soda, the Neutral salt will be a Glauber's salt; if putrefied urine, the Neutral salt will be a vitriolic Ammoniacal salt. Some of these salts incorporate with the Alum, which in large works crystallizes in vast lumps: and hence it comes that some sorts of Alum when mixed with a fixed Alkali smell like a volatile Alkali.

The crystals of Alum are octaedral, that is, they are solids with eight sides. These octaedral solids are triangular pyramids, having their angles cut away, so that four of their surfaces are hexagons, and the other four triangles.

Sulphur, Vitriol, and Alum are the three principal subjects in which we certainly know that the universal or Vitriolic Acid particularly resides, and from which we extract it when we want to have it pure. For this reason we thought it proper, before we treated of the extraction of this Acid, to shew the method of separating those matters themselves from the other minerals out of which we obtain them.

Moreover, all the other matrices, in which the Vitriolic Acid is most commonly lodged, may be referred to one or other of the matters which serve as bases to these three minerals.

To Sulphur we may refer all combinations of the Vitriolic Acid with an inflammable matter: but we must take care not to confound Sulphur with those Bitumens in which the Vitriolic Acid may be found: for the basis of those bitumens is a real Oil; whereas the basis of Sulphur is the pure Phlogiston. Yet as Oils themselves contain the Phlogiston, which, in union with the Vitriolic Acid forms a true Sulphur, it follows that such bitumens may in a certain respect be classed with Sulphur.

The same is to be said of Vitriol. The name is usually given to such combinations only as are formed of the Vitriolic Acid with Iron or Copper, which make the green and blue Vitriol; and to a third species of Vitriol, which is white, and has Zinc for its basis: but as the Vitriolic Acid may, by particular combinations, be united with many other metallic substances, all such Metallic Salts must be referred to the class of Vitriols.

The same may also be said of Alum, which is no other than a combination of the Vitriolic Acid with a particular kind of absorbent earth; so that all combinations of this Acid with any earth whatever may be placed in the same class.

This last class of mixts is the most extensive of all that contain the Vitriolic Acid; because there are a vast many earths, all differing from one another, with which that Acid may be united. Alum properly so called, the Gypsums, Talcs, Selenites, Boles, and all the other compounds of this kind, differ from each other only in their particular earths.

The different properties of these earthy salts depend on the nature of their bases. Those which are of the aluminous kind retain much water in crystallizing, which makes them very soluble in water, and gives them the property of acquiring readily the aqueous fluor when exposed to the fire. Those which are of the nature of the Selenites admit but very little water in their crystals, and consequently are almost insoluble in water; nor does the fire give them an aqueous fluor. Lastly, the Gypsums and Talcs are still more destitute of these properties. The natures of the earths in these several compounds are hitherto but very imperfectly known, and may give the Chymists occasion for inquiries equally curious and useful.

The Vitriolic Acid is sometimes found complicated with a fixed alkaline basis. This is almost always the Alkali of Sea-salt; so that the compound is a Glauber's Salt. Some mineral waters are impregnated therewith; which happens when these waters contain Vitriol or Alum, together with Sea-salt.

From the principles laid down, in our Elements of the Theory, it appears that the Vitriolic Acid hath not so great an affinity with earthy and metallic substances as with fixed Alkalis; and also that it is stronger than the Marine Acid, and hath a greater affinity with fixed Alkalis. This being allowed, the generation of native Glauber's Salts is easily accounted for. The Acid of aluminous or vitriolic Salts quits the earth or the metal with which it was combined, and expelling the Acid of Sea-salt unites with its basis. Warmth greatly promotes these decompositions.

If the common fossil salt, usually called Sal Gem, or any other kind of Sea-salt, should happen to be near a Volcano, when it discharges flaming Sulphur, as is frequently the case, and if this Sulphur should run among the Sea-salt, a Glauber's Salt would instantly be formed in that place; because when Sulphur burns, its Acid is separated and set at liberty.

Lastly, if aluminous or vitriolic matters, or burning Sulphur, should meet with the ashes of plants or trees consumed by fire, a vitriolated Tartar would be formed, because these ashes contain a fixed Alkali of the same nature with that of Tartar.

The Vitriolic Acid when combined with an earthy basis adheres strongly thereto; so that the force of fire is able to expel very little or none of it. There is no way of separating it from such a basis, but by presenting to it an Alkaline Salt, with which it will unite: nor is it ever extracted from such matters when it is required pure. It does not adhere so firmly to metallic substances; but is separated from them by the force of fire: so that it may be obtained from the several sorts of Vitriol. It is usually drawn from Green Vitriol; that being the commonest sort.

As to Sulphur, the Phlogiston which is its basis being the substance wherewith the Vitriolic Acid hath the greatest affinity, it would be altogether impossible to decompose it, and to separate its Acid, if it were not inflammable; but by burning it the Phlogiston is destroyed, and leaves the Acid at liberty. By this means therefore it may be separated. We shall now give the processes for extracting the Acid from Vitriol and Sulphur.

PROCESS IV.

Take any quantity of Green Vitriol: put it in an unglazed earthen vessel, and heat it gradually. Vapours will soon begin to rise. Increase the fire a little, and it will liquefy by means of the water contained in it, and acquire what we called an aqueous fluor. Continue the calcination, and it will become less and less fluid, grow thick, and turn of a greyish colour. Now raise your fire, and keep it up till the salt recover its solidity, acquire an orange colour, and begin to grow red where it immediately touches the sides of the vessel. Then take it out, and reduce it to powder.

Put the Vitriol thus calcined and pulverized into a good earthen retort, of which one half at least must remain empty. Set the retort in a reverberatory furnace: fit thereto a large glass receiver, and, having luted the joint well, give fire by degrees. You will soon see white clouds rise into the receiver, which will render it opaque, and heat it. Continue the same degree of fire till these clouds disappear: they will be succeeded by a liquor which will trickle down the sides of the receiver in veins. Still keep up the fire to the same degree as long as these veins appear. When they begin to abate, increase the fire, and push it to the utmost extremity: upon this, there will come over a black, thick liquor: it will even be found congealed, and prove the icy Oil of Vitriol, if care hath been taken to change the receiver, keep the vessels perfectly close, and give a sufficient degree of heat. Proceed thus till nothing more comes over, or at least very little. Let the vessels cool, unlute them, pour the contents of the receiver into a bottle, and seal it hermetically.

OBSERVATIONS.

Green Vitriol retains much water in crystallizing; and, in order to free it from that superfluous phlegm, it must be calcined before you distil it. Without this precaution the operation will be exceedingly protracted, and a great deal of time wasted in distilling such a quantity of water; which will moreover greatly weaken the Acid by commixing with it, unless care be taken to change the recipient as soon as the water is all come over.

But there is also another advantage in calcining the Vitriol before you put it into the retort: for otherwise this salt would melt on the first application of heat, and run into a mass; which would prove a great hindrance to its distillation. This inconvenience is avoided by a previous calcination, in consequence whereof the Vitriol is easily reduced to a powder which never becomes fluid.

Vitriol calcined as directed in the process grows so hard, and adheres so firmly to the vessel in which the calcination is performed, that it requires no small pains to separate and pulverize it. Care must be taken to put it into the retort as soon as it is pulverized, and to stop that vessel very close if you do not begin the distillation immediately: for otherwise it will naturally attract from the air almost all the moisture it hath lost.

The Acid which Vitriol yields by distillation is sulphureous; probably because it still retains some of the Phlogiston, with which it was united when under the form of sulphur in the Pyrites; or else hath laid hold on a portion of that belonging to the iron which served for its basis in Vitriol. But this sulphureous part is volatile, and flies off in time.

This decomposition of Vitriol in close vessels is a difficult and laborious process. To carry the operation to its utmost perfection requires a fire of extreme violence, kept up without intermission during four or five days; such in short as few vessels are able to bear. Of course this operation is seldom performed in laboratories. The French Chymists fetch their Oil of Vitriol from Holland, where it is extracted from Vitriol in large quantities, by means of furnaces erected for the purpose, in which many retorts are employed at once.

In the Memoirs of the Academy of Sciences M. Hellot hath given us the most material circumstances of a very fine experiment of this kind, in which he pushed the distillation of Green Vitriol to the utmost. Into a German retort[5] he put six pounds of Green English Vitriol calcined to redness, which he exposed to a fire of the extremest violence, constantly kept up during four days and four nights. At the expiration of that time he found in the vessels employed as receivers an Icy Oil of Vitriol, which was altogether in a crystalline form and black. The precautions necessary to make this experiment succeed, he represents, in the following terms.

"The success of this operation, which produces an Oil of Vitriol perfectly Icy and without any liquor, depends on the care taken to prevent the acid vapours, driven by the fire out of Vitriol calcined to redness, from having any communication with the external air while they are distilling: for otherwise they will attract from it a moisture which will keep them fluid in the receiver. The receiver must be at such a distance from the furnace that it may remain cool enough for the vapours to condense in it. There must also be sufficient room for those vapours to circulate in, and to prevent the sulphureous explosions, which are every now and then discharged out of the retort, from bursting the vessels: for though the previous calcination of the Vitriol hath carried off the most volatile, yet there still remains enough of the inflammable principle, even in the iron itself, to form a Sulphur with the Acid as it is extricated, or at least a mixt that would be as apt to take fire as common Sulphur, if it were not over-dosed with the Acid.

"As the best means of gaining these ends, M. Hellot contrived to adapt to the neck of his retort a receiver with two necks, the lowermost of which was inserted into a large ballon. Receivers applied to each other in this manner are called Adopters.

"It is no easy matter to get this Icy Oil out of the ballon: for as soon as the air touches it such a thick cloud of sulphureous fumes arises, that it is absolutely necessary to place the vessel on some shelf over head, because a man cannot stand exposed thereto for a single minute without being suffocated."

This Icy Acid must be shut up with all possible expedition in a crystal bottle accurately closed with a glass stopple, which should be ground with emery in its neck so as to fit it exactly: for it attracts moisture so powerfully, that, unless exceeding great care be taken to prevent all communication with the external air, it will soon dissolve into a fluid.

"The Icy Oil is black; because the acid vapours carry over with them something of a greasy matter, from which Vitriol is seldom free, and which always appears, after repeated solutions and crystallizations of this Salt, in the mother-water which will shoot no more. Now the smallest portion of inflammable matter presently blackens the most highly rectified Oil of Vitriol, which is perfectly clear.

"The Vitriolic Acid, when forced over by a violent heat, carries along with it some ferruginous particles also, that want nothing but to be united with a phlogiston to become true iron. They are easily discovered, either in the common black Oil of Vitriol, or in the blackish crystals of the Icy Oil, by only dissolving them in a large quantity of distilled water: for after seven or eight days digestion a light powder or downy sediment precipitates, which being calcined in a violent fire is partly attracted by the magnet; and being again calcined with bees-wax becomes almost entirely iron."

The Caput mortuum of this distillation of Vitriol is the ferruginous earth of this Salt, and is called Colcothar. When this Colcothar hath undergone a violent fire, as in the experiment now related, scarce any Acid remains therein. Out of six pounds of Vitriol that M. Hellot used, he could recover no more, by lixiviating what was left in the retort, than two ounces of a Vitriolic Salt; and even that was very earthy.

If Vitriol be exposed to a fire neither so violent nor so long continued, its Colcothar will yield a greater quantity of Vitriol that hath not been decomposed. A white crystalline salt is also obtained from it, and called Salt of Colcothar; which is no other than the small portion of Alum usually contained in Vitriol, and not so easily decomposed by the the action of fire.

PROCESS V.

In the burning of Sulphur, the Phlogiston which serves for its basis is dissipated, and separated from the acid which is left at liberty. The acid fumes which rise from the lighted sulphur strike against the inside of the head placed over it, are there condensed, and appear in the form of a liquor. But as Sulphur, like all other inflammable bodies, Nitre excepted, will not burn in close vessels, it is necessary that the air be freely admitted here; which occasions the loss of a great deal of the Acid of the Sulphur, as is evident from the pungent suffocating smell perceived in the laboratory during the operation.

This Acid, while combined with the Phlogiston, is incapable of contracting any union with water; but when alone is very apt to mix therewith: it is even proper to put some in its way, that it may incorporate therewith as soon as it is discharged from the Sulphur; for it is then very free from phlegm, very volatile, and consequently very little disposed to condense into a liquor, but, on the contrary, very apt to fly off in vapours. The water, which it imbibes with a kind of avidity, fixes and detains it; so that by this means a much greater quantity thereof is obtained from Sulphur, than if it were distilled without this precaution.

It is proper, therefore, now and then, to introduce a dish full of hot water under the head which receives the fumes of the Sulphur. The vapours that exhale from the water be-dew the inside of the head, and procure the advantage we are speaking of.

The same thing may be effected several other ways: thus, the crucible containing the Sulphur may be set on a foot placed in an earthen dish with some water in it; which, however, must not rise above the foot; for if it should reach the crucible, it might cool and fix the sulphur. The dish thus prepared must be placed on a sand-bath hot enough to make the water smoke continually; and over all is to be placed the head as directed in the process.

The size and form of the vessel which immediately receives the sulphureous fumes may also contribute to increase the quantity of the Acid Spirit. A very large vessel, with a hole at bottom no wider than is just sufficient to admit the vapours, is the properest for this operation.

After the Sulphur has burnt for some time, it often happens that a sort of skin or crust forms on its surface, which is not inflammable, but gradually lessens the quantity and vigour of the flame as it increases in thickness, and at last puts it quite out. This crust proceeds from the impurities, and heterogeneous uninflammable particles contained in the sulphur. Care must be taken to remove it with an iron wire as fast as it forms.

Two quantities of sulphur may also be kept in two crucibles, and heated alternately. That in which the Sulphur is hot and melted may be substituted for the other in which the Sulphur is grown cold and fixed; because cold Sulphur does not burn well.

The Spirit of Sulphur is at first pungent and volatile, because it still retains a small portion of the Phlogiston: but that sulphureous part flies off, especially if the bottle in which the Spirit is kept be left for some time unstopped.

The Acid obtained from Sulphur appears by all chymical proofs perfectly like that obtained from Vitriol: they differ in this only, that the former is the purest; for the Acid obtained from Vitriol carries over with it some metallic parts, as we observed before, which can never happen to that obtained from Sulphur.

If linen rags dipped in a solution of Fixed Alkali be exposed to the fumes of burning brimstone, the Spirit of Sulphur joins with the Alkali, and therewith forms a Vitriolated Tartar. This Salt is known to be formed when the rags grow stiff, and appear spangled with a vast many glittering points, which are nothing but little crystals of the Salt we are speaking of.

When the Sulphur burns very gently and slowly the Spirit that exhales from it is so much the more sulphureous and volatile: and hence the Salt formed by the combination of this Spirit with the Alkali exposed to it in linen rags, as in the above-mentioned experiment, is not at first a Vitriolated Tartar; but a Neutral Salt of a particular kind, which is capable of being decomposed by any other Mineral Acid, the sulphureous Acid having less affinity than any of the rest with Alkalis. Nevertheless, this Salt becomes in time a true Vitriolated Tartar, because the sulphureous part which weakened its Acid easily quits it and flies off.

PROCESS VI.

Take the Vitriolic Acid you intend to concentrate, that is, to dephlegmate and make stronger: pour it into a good glass retort, of such a size that your quantity of Acid may but half fill it: set this retort in the sand-bath of a reverberating furnace: fit to it a receiver; lute it on, and give a gradual fire. There will come over into the receiver a clear liquor, the first drops of which will be but faintly acid: this is the most aqueous part.

When the drops begin to follow one another much more slowly, raise your fire, till the liquor begin to bubble a little in the middle. Keep it thus gently boiling, till one half or two thirds thereof be come over into the receiver. Then let your vessels cool; unlute them; what remains in the retort pour into a crystal bottle, and stop it exactly with a glass stopple rubbed with emery.

OBSERVATIONS.

The Acid obtained from Sulphur is generally very aqueous; either because in preparing it water must necessarily be administered, that it may unite therewith as it separates from the Sulphur; or because it is so greedy of moisture as to attract a great deal from the air, which must needs be admitted to make the Sulphur burn.

The Acid obtained from Vitriol, excepting that which rises last, is also mixed with a pretty considerable quantity of phlegm; because the Vitriol, though calcined, still retains a great deal thereof, which rises with the Acid in distillation. Now, as there are many chymical experiments that will not succeed without Acids exceedingly dephlegmated, it is proper to have in a laboratory all the Acids thus conditioned; because if they happen to be too strong for particular operations, as is sometimes the case, it is very easy to lower them to the desired degree, by adding a sufficient quantity of water.

The Vitriolic Acid is much heavier and much less volatile than water. If therefore a mixture of these two liquors be exposed to the fire, the aqueous part will rise with a degree of heat which is not able to carry up the Acid: by this means they may be separated from each other; and thus is the Vitriolic Acid concentrated.

Nevertheless, as this Acid combines most closely with water, and is in a manner strongly connected with it, the water carries up some portion thereof along with it; and hence it comes, that the liquor which rises into the receiver is acid: it is called Spirit of Vitriol.

As the fire carries off the most aqueous part, the other which remains in the retort increases in specific gravity. The Acid particles are brought nearer together, retain the aqueous particles more obstinately, and therefore to separate them the degree of heat must be increased.

It is usual to draw off one half or two thirds of the liquor that was put into the retort: but this depends on the degree of strength the Acid was of before concentration, and the degree of concentration intended to be given it.

If the Acid to be concentrated be Oil of Vitriol, from being brown or black it grows clearer as the operation advances, and at last becomes perfectly colourless and transparent; because the fat matter which tinged it black is dissipated during the process. Some of it deposites a white crystalline earth.

A sulphureous smell is generally perceived about the vessels in this operation. This arises from a small portion of the Phlogiston from which the Acid is not free; and it is this inflammable matter which gives the Oil of Vitriol its black colour: for the clearest and best rectified Oil of Vitriol will become brown, and even black, in a short time, if any inflammable matter, though in a very small quantity, be dissolved therein.

The vessels are luted in this operation, to prevent any loss of the Spirit of Vitriol, which being very acid is of use in many chymical experiments, and may itself also be again concentrated.

We observed, that in this operation it is necessary the retort should be of very good glass. Indeed the Acid is so active, and so strong, that if the glass be tender and have a little too much salt in its composition, it will be so corroded thereby that it will fall to pieces.

Though we directed the retort to be set in a sand-bath for this operation, it does not follow that it may not also be placed in a naked fire: on the contrary, when the heat is not conveyed through a bath the operation advances faster, and is much less tedious. But then great caution must be used, and the closest attention given to the management of the fire, which must be raised by almost imperceptible degrees, especially at the beginning of the operation; otherwise it is next to a certainty that the vessels will break. In general, a naked fire may be employed in almost all distillations which require a greater degree of heat than that of boiling water, or the balneum mariæ: the operation will be sooner finished; but it requires an experienced hand, that has by practice acquired a habit of governing the fire with judgment.