But it being observed that fire, applied to the decomposition of

bodies, most commonly alters their secondary principles very sensibly,

by combining them in a different manner with each other, or even partly

decomposing them, and reducing them to their primitive principles;

other means have been used to separate those principles without the

help of fire.

With this view the mixts to be decomposed are forcibly compressed, in

order to squeeze out of them all such parts of their substance as they

will by this means part with: or else those mixts are for a long time

triturated, either along with water, which carries off all their saline

and saponaceous contents, or with solvents, such as ardent spirits,

capable of taking up every thing in them that is of an oily or resinous

nature.

We shall here give a succinct account of the effects of these different

methods, as applied to the principal substances among Vegetables and

Animals, and likewise to some Minerals.

SECTION I.

_The_ ANALYSIS _of_ VEGETABLE SUBSTANCES.

A vast many vegetable substances, such as kernels and seeds, yield,

by strong compression, great quantities of mild, fat, unctuous Oils,

which are not soluble in ardent spirits: these are what we called

_Expressed Oils_. They are also sometimes called _Fat Oils_, on account

of their unctuousness, in which they exceed all other sorts of Oil. As

these oils are obtained without the aid of fire, it is certain that

they existed in the mixt just as we see them, and that they are not in

the least altered: which could not have been the case had they been

obtained by distillation; for that never produces any Oils but such as

are acrid and soluble in spirit of wine.

Some vegetable matters, such as the rind of citrons, lemons, oranges,

_&c._ also yield, only by being squeezed between the fingers, a great

deal of Oil. This spirts out in fine small jets, which being received

upon any polished surface, such as a looking glass, run together and

form a liquor that is a real Oil.

But it must be carefully noted, that this sort of Oil, though obtained

by expression only, is nevertheless very different from the Oils

mentioned before, to which the title of _Expressed Oils_ peculiarly

belongs: for this is far lighter and thinner; moreover, it retains the

perfect odour of the fruit which yields it, and is soluble in spirit

of wine; in a word, it is a true essential Oil, but abounds so in

the fruits which produce it, and is lodged therein in such a manner,

occupying a vast number of little cells provided in the peel for its

reception, that a very slight pressure discharges it; which is not the

case with many other vegetables that contain an essential Oil.

Succulent and green plants yield by compression a great deal of liquor

or juice, which consists of most of the phlegm, of the salts, and a

small portion of the oil and earth of the plant. These juices, being

set in a cool place for some time, deposite saline crystals, which are

a combination of the acid of the plant with part of its oil and earth,

wherein the acid is always predominant. These salts, as is evident from

the description here given, bear a great resemblance to the tartar

of wine treated of above. They are called _Essential Salts_; so that

Tartar might likewise be called the _Essential Salt of Wine_.

Dried plants, and such as are of a ligneous, or acid nature, require to

be long triturated with water, before they will yield their essential

salts. Trituration with water is an excellent way to get out of them

all their saline and saponaceous contents.

A vegetable matter that is very oily yields its essential salt with

much difficulty, if at all; because the excessive quantity of oil

entangles the salt so that it cannot extricate itself or shoot into

crystals. Mr. Gerike, in his _Principles of Chymistry_, says, that

if part of the oil of a plant be extracted by spirit of wine, its

essential salt may be afterwards obtained with more ease and in greater

quantity. This must be a very good method for such plants as have an

excessive proportion of essential oil; but will not succeed if the

essential salt be hindered from crystallizing by a redundancy of fat

oil, because fat oils are not soluble in spirit of wine.

Essential Salts are among those substances which cannot be extracted

from mixts by distillation: for the first impression of fire decomposes

them.

Though the acid which predominates in the Essential Salts of plants,

be most commonly analogous to the vegetable acid, properly so called,

that is, to the acid of vinegar and tartar, which is probably no other

than the vitriolic acid disguised; yet it sometimes differs therefrom,

and somewhat resembles the nitrous or the marine acid. This depends

on the places where the plants grow which produce these salts: if

they be maritime plants, their acid is akin to the acid of sea-salt;

if on the contrary they grow upon walls, or in nitrous grounds, their

acid is like that of nitre. Sometimes one and the same plant contains

salts analogous to all the three mineral acids; which shews that the

vegetable acids are no other than the mineral acids variously changed

by circulating through plants.

Liquors containing the Essential Salts of plants being evaporated by a

gentle heat to the consistence of honey, or even further, are called

_Extracts_. Hence it is plain, that an Extract is nothing but the

essential salt of a plant, combined with some particles of its oil and

earth, that remained suspended in the liquor, and are now incorporated

by evaporation.

Extracts of plants are also prepared by boiling them long in water, and

then evaporating some part of it. But these Extracts are of inferior

virtue; because the fire dissipates many of the oily and saline parts.

EMULSIONS.

Substances which abound much in Oil, being bruised and triturated

with water for some time, afford a liquor of an opaque dead-white

colour, like milk. This liquor consists of such juices as the water is

capable of dissolving, together with a portion of the oil, which being

naturally indissoluble in water, is only divided and dispersed in the

liquor, the limpidity whereof is by that means destroyed. This sort of

oily liquor, in which the oil is only divided, not dissolved, is called

an _Emulsion_. The oily particles in Emulsions spontaneously separate

from the water, when left at rest, and uniting into greater masses

rise, on account of their lightness, to the surface of the liquor,

which by that means recovers a degree of transparency.

If vegetables abounding in essential oils and resins be digested in

spirit of wine, the menstruum takes up these oily matters, as being

capable of dissolving them; and they may afterwards be easily separated

from it by the affusion of water. The water, with which spirit of wine

has a greater affinity than with oily matters, separates them by this

means from their solvent, agreeably to the common laws of affinities.

Without the help of fire, scarce any thing, besides the substances

already mentioned, can be obtained from a plant: but, by the means

of distillation, we are enabled to analyse them more completely.

In prosecuting this method of extracting from a plant the several

principles of which it consists, the following order is to be observed.

A plant being exposed to a very gentle heat, in a distilling vessel set

in the _balneum mariæ_, yields a water which retains the perfect smell

thereof. Some Chymists, and particularly the illustrious Boerhaave,

have called this liquor the _Spiritus Rector_. The nature of this

odoriferous part of plants is not yet thoroughly known; because it is

so very volatile that it is difficult to subject it to the experiments

necessary for discovering all its properties.

If, instead of distilling the plant in the _balneum mariæ_, it be

distilled over a naked fire, with the precaution of putting a certain

quantity of water into the distilling vessel along with it, to prevent

its suffering a greater heat than that of boiling water, all the

essential oil contained in that plant will rise together with that

water, and with the same degree of heat.

On this occasion it must be observed, that no essential oil can be

obtained from a plant after the _Spiritus Rector_ hath been drawn off;

which gives ground to think that the volatility of these oils is owing

to that spirit.

The heat of boiling water is also sufficient to separate from vegetable

matters the fat oils which they contain. That, however, is to be done

by the way of decoction only, and not by distillation: because, though

these oils will swim on water, yet they will not rise in vapours

without a greater degree of heat.

When the essential oil is come over, if the plant be exposed to a

naked fire, without the addition of water, and the heat be increased

a little, a phlegm will rise that gradually grows acid; after which,

if the heat be increased as occasion requires, there will come over a

thicker and heavier oil; from some a volatile alkali; and last of all,

a very thick, black, empyreumatic oil.

When nothing more rises with the strongest degree of heat, there

remains of the plant a mere coal only, called the _Caput Mortuum_, or

_Terra Damnata_. This coal when burnt falls into ashes, which, being

lixiviated with water, give a fixed alkali.

It is observable, that in the distillation of plants which yield

an acid and a volatile alkali, these two salts are often found

quite distinct and separate in the same receiver; which seems very

extraordinary, considering that they are naturally disposed to

unite, and have a great affinity with one another. The reason of

this phenomenon is, that they are both combined with much oil, which

embarrasses them so that they cannot unite to form a neutral salt, as

they would not fail to do were it not for that impediment.

All vegetables, except such as yield a great deal of volatile alkali,

being burnt in an open fire, and so as to flame, leave in their ashes

a large quantity of an acrid, caustic, fixed alkali. But if care be

taken to smother them, so as to prevent their flaming while they burn,

by covering them with something that may continually beat down again

what exhales, the salt obtained from their ashes will be much less

acrid and caustic; the cause whereof is, that some part of the acid

and oil of the plant being detained in the burning, and stopped from

being dissipated by the fire, combines with its alkali. These salts

crystallize, and, being much milder than the common fixed alkalis, may

be used in medicine, and taken internally. They are called _Tachenius's

Salts_, because invented by that Chymist.

Marine plants yield a fixed alkali analogous to that of sea-salt.

As for all other plants or vegetable substances, the fixed alkalis

obtained from them, if rightly prepared and thoroughly calcined, are

all perfectly alike, and of the very same nature.

The last observation I have to make on the production of fixed alkalis

is, that if the plant you intend to work upon be steeped or boiled

in water before you burn it, a much smaller quantity of salt will

be obtained from it; nay, it will yield none at all, if repeated

boilings have robbed it entirely of those saline particles which must

necessarily concur with its earth to form a fixed Alkali.

SECTION II.

_The_ ANALYSIS _of_ ANIMAL SUBSTANCES.

Succulent animal substances, such as new-killed flesh, yield by

expression a juice or liquid, which is no other than the phlegm,

replete with all the principles of the animal body, except the earth,

of which it contains but little. The hard or dry parts, such as the

horns, bones, _&c._ yield a similar juice, by boiling them in water.

These juices become thick, like a glue or jelly, when their watery

parts are evaporated; and, in this state, they are truly extracts of

animal matters. These juices afford no crystals of essential salt,

like those obtained from vegetables, and shew no sign either of an acid

or an alkali.

Great part of the oil which is in the flesh of animals may be easily

separated without the help of fire; for it lies in a manner by itself:

it is commonly in a concrete form, and is called _Fat_. This oil

somewhat resembles the fat oils of vegetables; for like them it is

mild, unctuous, indissoluble in spirit of wine, and is subtilized and

attenuated by the action of fire. But there is not in animals, as in

vegetables, any light essential oil, which rises with the heat of

boiling water; so that, properly speaking, animals contain but one sort

of oil.

Few animal substances yield a perceptible acid. Ants and bees are

almost the only ones from which any can be obtained: and indeed the

quantity they yield is very small, as the acid itself is extremely weak.

The reason thereof is, that as animals do not draw their nourishment

immediately from the earth, but feed wholly either on vegetables or

on the flesh of other animals, the mineral acids, which have already

undergone a great change by the union contracted between them and

the oily matters of the vegetable kingdom, enter into a closer union

and combination with these oily parts while they are passing through

the organs and strainers of animals; whereby their properties are

destroyed, or at least so impaired, that they are no longer sensible.

Animal matters yield in distillation, first, a phlegm, and then, on

increasing the fire, a pretty clear oil, which gradually becomes

thicker, blacker, more fetid, and empyreumatic. It is accompanied

with a great deal of volatile alkali; and if the fire be raised

and kept up till nothing more comes over, there will remain in the

distilling vessel a coal like that of vegetables; except that when it

is reduced to ashes, no fixed alkali, or at least very little, can be

obtained from them, as from the ashes of vegetables. This arises from

hence, that, as we said before, the saline principle in animals being

more intimately united with the oil than it is in plants, and being

consequently more attenuated and subtilized, is too volatile to enter

into the combination of a fixed alkali; on the contrary, it is more

disposed to join in forming a volatile alkali, which on this occasion

does not rise till after the oil, and therefore must certainly be the

production of the fire. It must be observed, that all we have hitherto

said concerning the analysis of bodies must be understood of such

matters only as have not undergone any sort of Fermentation.

The chyle and milk of animals which feed on plants still retain some

likeness to vegetables; because the principles of which these liquors

are composed have not gone through all the changes which they must

suffer before they enter into the animal combination.

Urine and sweat are excrementitious aqueous liquors, loaded chiefly

with the saline particles which are of no service towards the

nourishment of the animal, but pass through its strainers without

receiving any alteration; such as the neutral salts which have a fixed

alkali for their basis, and particularly the sea-salt, which happens

to be in the food of animals, whether it exist therein naturally, as

it does in some plants, or whether the animals eat it to please their

palates.

The saliva, the pancreatic juice, and especially the bile, are

saponaceous liquors, that is, they consist of saline and oily particles

combined together: so that being themselves dissolved in an aqueous

liquor, they are capable of dissolving likewise the oily parts, and of

rendering them miscible with water.

Lastly, the blood being the receptacle of all these liquors partakes of

the nature of each, more or less in proportion to the quantity thereof

which it contains.

SECTION III.

_The_ ANALYSIS _of_ MINERAL SUBSTANCES.

Minerals differ greatly from vegetables, and from animals; they are

not near so complex as those organized bodies, and their principles

are much more simple; whence it follows, that these principles are

much more closely connected, and that they cannot be separated without

the help of fire; which not having on their parts the same action and

the same power as on organized bodies, hath not the same ill effect

on them; I mean the effect of changing their principles, or even

destroying them entirely.

I do not here speak of pure, vitrifiable, or refractory earths; of

mere metals and semi-metals; of pure acids; or even of their simplest

combinations, such as sulphur, vitriol, alum, sea-salt: of all these we

have said enough.

We are now to treat of bodies that are more complex, and therefore more

susceptible of decomposition. These bodies are compound masses, or

combinations of those above-mentioned; that is, metallic substances as

they are found in the bowels of the earth, united with several sorts

of sand, stones, earths, semi-metals, sulphur, _&c._ When the metallic

matter is combined with other matters, in such a proportion to the

rest that it may be separated from them with advantage and profit,

these compounds are called _Ores_; when the case is otherwise, they are

called _Pyrites_, and _Marcasites_; especially if sulphur or arsenic be

predominant therein, which often happens.

In order to analyse an ore, and get out of it the metal it contains,

the first step is to free it from a great deal of earth and stones,

which commonly adhere to it very slightly and superficially. This

is effected by pounding the ore, and then washing it in water; to

the bottom of which the metalline parts presently sink, as being the

heaviest, while the small particles of earth and stone remain suspended

some time longer.

Thus the metallic part is left combined with such matters only as are

most intimately complicated with it. These substances are most commonly

sulphur and arsenic. Now, as they are much more volatile than other

mineral matters, they may be dissipated in vapours, or the sulphur may

be consumed, by exposing the ore which contains them to a proper degree

of heat. If the sulphur and arsenic be desired by themselves, the fumes

thereof may be catched and collected in proper vessels and places. This

operation is called _Roasting_ an Ore.

The metal thus depurated is now fit to be exposed to a greater force of

fire, capable of melting it.

On this occasion the semi-metals and the imperfect metals require

the addition of some matter abounding in phlogiston, particularly

charcoal-dust; because these metallic substances lose their phlogiston

by the action of the fire, or of the fluxes joined with them, and

therefore without this precaution would never acquire either the

splendour or the ductility of a metal. By this means the metallic

substance is more accurately separated from the earthy and stony parts,

of which some portion always remains combined therewith till it is

brought to fusion. For, as we observed before, a metallic glass or calx

only will contract an union with such matters; a metal possessed of its

phlogiston and metalline form being utterly incapable thereof.

We took notice of the cause of this separation above, where we shewed

that a metal possessed of its phlogiston and metalline form will not

remain intimately united with any calcined or vitrified matter, not

even with its own calx or glass.

The metal therefore on this occasion gathers into a mass, and lies

at the bottom of the vessel, as being most ponderous; while the

heterogeneous matters float upon it in the form of a glass, or a

semi-vitrification. These floating matters take the name of _Scoriæ_,

and the metalline substance at bottom is called the _Regulus_.

It frequently happens, that the metalline regulus thus precipitated

is itself a compound of several metals mixed together, which are

afterwards to be separated. We cannot at present enter into a detail

of the operations necessary for that purpose: they will appear in our

Treatise of _Practical Chymistry_: but the principles on which they are

founded may be deduced from what we have said above, concerning the

properties of the several metals and of acids.

It is proper to observe, before we quit this subject, that the rules

here laid down for analysing ores are not absolutely general: for

example, it is often adviseable to roast the ore before you wash it;

for by that means some ores are opened, attenuated, and made very

friable, which would cost much trouble and expence, on account of their

excessive hardness, if you should attempt to pound them without a

previous torrefaction.

It is also frequently necessary to separate the ore from part only

of its stone; sometimes to leave the whole; and sometimes to add

more to it, before you smelt it. This depends on the quality of the

stone, which always helps to promote fusion when it is in its own

nature fusible and vitrifiable. It is then called the _Fluor_ of the

ore: but of this we must say, as we did of the preceding article, it

is sufficient for our present purpose to lay down the fundamental

principles on which the reason of every process is built; the

description of the operations themselves being reserved for our second

Part.

We shall now give a succinct account of the principal ores and mineral

bodies, contenting ourselves with just pointing out the particulars of

which they severally consist.

_Of the_ PYRITES.

_The yellow Pyrites._

The yellow Pyrites is a mineral consisting of sulphur, iron, an

unmetallic earth, and frequently a little copper: the sulphur, which

is the only one of these principles that is volatile, may be separated

from the rest by sublimation: it usually makes a fourth, and sometimes

a third, of the whole weight of these Pyrites. The other principles are

separated from one another by fusion and reduction with the phlogiston,

which, by metallizing the ferruginous and cupreous earths, parts

them from the unmetallic earth: for this earth vitrifies, and cannot

afterwards continue united with metallic matters possessed of their

metalline form, as hath been said before.

There is yet another way of decomposing the yellow Pyrites, which is to

let it ly till it effloresces, or begins to shoot into flowers; which

is nothing but a sort of slow accension of the sulphur it contains.

The sulphur being by this means decomposed, its acid unites with the

ferruginous and cupreous parts of the Pyrites, and therewith forms

green and blue vitriols; which may be extracted by steeping in water

the Pyrites which has effloresced or been burnt, and then evaporating

the lixivium to a pellicle; for by this means the vitriol will shoot

into crystals.

Sometimes the Pyrites contains also an earth of the same nature with

that of alum; a Pyrites of this sort, after flowering, yields alum as

well as vitriol.

_The white Pyrites._

The white Pyrites contains much arsenic, a ferruginous earth, and an

unmetallic earth. The arsenic, being a volatile principle, may be

separated by sublimation or distillation from the rest, which are

fixed: and these again may be disjoined from each other by fusion and

reduction, as was said in relation to the yellow Pyrites.

_The Copper Pyrites._

The Copper Pyrites contains sulphur, copper, and an unmetallic earth.

A great deal thereof likewise holds arsenic, and its colour approaches

more or less to orange, yellow, or white, according to the quantity of

arsenic in it. It may be decomposed by the same means as the yellow and

white Pyrites.

_Of_ ORES.

_Of Gold Ores._

Gold being constantly found in its metalline form, and never combined

with sulphur and arsenic, its matrices are not, properly speaking,

ores; because the metal contained in them is not mineralized. The

gold is only lodged between particles of stone, earth, or sand, from

which it is easily separated by lotion, and by amalgamation with

quick-silver. The gold thus found is seldom pure, but is frequently

alloyed with more or less silver, from which it is to be separated by

quartation.

It is also very common to find gold in most ores of other metals or

semi-metals, and even in the Pyrites; but the quantity contained

therein is generally so small, that it would not pay the cost of

extracting it. However, if any should incline to attempt it, merely

out of curiosity, it would be necessary to begin with treating these

ores in the manner proper for separating their metalline part; then to

cupel the metalline regulus so obtained; and, lastly, to refine it by

quartation.

_Of Silver Ores._

It is no rare thing to find silver, as well as gold, in its metalline

form, only lodged in sundry earths and stony matters, from which it may

be separated in the same manner as gold. But the greatest quantities

of this metal are usually dug out of the bowels of the earth in a

truly mineral state: that is, combined with different substances, and

particularly with sulphur and arsenic.

Several silver ores are distinguished by peculiar characteristics, and

are accordingly denoted by particular names. That which is called the

_Vitreous Silver Ore_, is scarce any thing else but a combination of

silver and sulphur. Another is known by the name of the _Horny Silver

Ore_, because when in thin plates it is semi-transparent: in this ore

the silver is mineralized by sulphur and a little arsenic. The _Red

Silver Ore_ is of the colour which its name imports, sometimes more,

sometimes less vivid; and is chiefly composed of silver, arsenic, and

sulphur: it also contains a little iron.

These three ores are very rich in silver: the first contains nearly

three fourths of its weight, and the others about two thirds of theirs.

There is a fourth, called the _White Silver Ore_, which, though it be

heavier, is not so rich in silver, because it contains much copper.

Many other minerals contain silver, yet are not, properly speaking,

silver ores; because a much greater quantity of other metals than of

silver is found in them.

When a silver ore is to be decomposed, in order to have the silver

pure, or when silver is to be extracted out of any ore that contains

it, the first thing to be done is to roast the ore, in order to clear

it of the volatile minerals: and as silver cannot be had pure without

the operation of the cupel, which requires more or less lead to be

joined with it, it is usual to mix with the torrified silver ore a

quantity of lead, proportioned to that of the heterogeneous matters

combined with the silver, and to melt the whole together. Part of the

added lead vitrifies during the fusion, and at the same time converts

some of the heterogeneous matters also into glass, with which it forms

a scoria that rises to the surface of the matter. The other part of the

lead, with which the silver is mixed, falls to the bottom in the form

of a regulus, which must be cupelled in order to have the silver pure.

_Of Copper Ores._

Copper is much seldomer found in a metalline form than gold or silver:

it is commonly in a mineral state: it is mineralized by sulphur and

arsenic: almost all its ores contain also more or less of iron;

sometimes a little silver, or even gold, together with unmetallic

earths and stones, as all ores do.

Most copper ores are of a beautiful green or blue, or else in shades

blended of these two colours. The minerals called _mountain green_, and

_mountain blue_, are true copper ores; not in the form of hard stones,

like other ores, but crumbly and friable like earth.

Nevertheless, there are several copper ores of different colours, as

ash-coloured, whitish, and shaded with yellow or orange; which colours

arise from the different proportions of arsenic, sulphur, and iron,

which these ores contain.

In order to decompose a copper ore, and to extract the copper it

contains, it is first of all to be freed from as many of its earthy,

stony, sulphureous, and arsenical parts, as is possible, by roasting

and washing; then what remains is to be mixed with a flux, compounded

of a fixed alkali and some inflammable matter; a little sea-salt is

to be put over all, and the whole melted by a strong fire. The salts

facilitate the fusion and scorification of the unmetallic matters, and

therewith form a slag, which being the lightest rises to the surface.

The metalline matters are collected below in the form of a shining

regulus of copper; which, however, is not usually fine copper, but

requires to be purified in the manner to be shewn in our second part.

In order to separate the copper from the unmetallic matters, it is

absolutely necessary to melt its ore along with inflammable substances

abounding in phlogiston. For, as this metal is not possessed of its

metalline form while it is in a mineral state, as it is destitute of

the true quantity of phlogiston, and, though it were not, would lose it

by the action of the fire, it would come to pass, that if its ore were

melted without the addition of any inflammable matter, the cupreous

earth or calx would be scorified and confounded with the unmetallic

matters; and as all metallic matters, except gold and silver, are

subject to this inconvenience as well as copper, the addition of an

inflammable substance, in fluxing all ores that contain them, is a

general rule that ought constantly to be observed.

_Of Iron Ores._

Iron is seldom found pure and malleable in the earth; yet it is much

seldomer found in the mineral state, properly so called, than any of

the other metals: for most iron ores are scarce any thing more than a

ferruginous earth mixed in different proportions with unmetallic earths

and stones. Some of them, however, contain also volatile minerals, such

as sulphur and arsenic; and therefore it is necessary to roast the iron

ores, like all others, before you attempt to extract the metal out of

them. That being done, they are to be smelted with a flux consisting of

fusible and inflammable matters, as the general rule directs.

Iron is the commonest of all metals: nay, it is so universally diffused

through the earth, that it is difficult to find any stone, earth, or

sand, that does not contain some of it; and therefore none of these are

usually considered and treated as iron ores, except such as contain a

great deal of that metal, and melt easily. The hematites, emery, yellow

pyrites, calamine, all contain a pretty considerable quantity of iron;

but no body attempts to extract it from them, because they are very

hard to melt.

Ferruginous earth being naturally of an orange colour, a stone or earth

may be judged to contain iron, if either naturally, or after roasting,

it appears to have one shade of yellow or red.

The singular property which iron has of being attracted by the magnet,

and of being the only body, exclusive of all others, that is so,

likewise affords us an easy method of discovering the presence of

this metal among other matters, where it often exists in such a small

quantity that it could not otherwise be found out. For this purpose

the body in which iron is suspected to lurk, must be pulverised and

torrefied with some inflammable matter; and then the powder thus

roasted being touched with a magnet, or an animated bar, if it contains

any particles of iron they will infallibly adhere to the magnet or bar.

_Of Tin Ores._

Tin is never found in the earth pure and malleable, but always in a

mineral state, and always mineralized by arsenic. Tin ores are not

sulphureous; whence it comes, that though tin be the lightest of all

metals, its ores are nevertheless heavier than those of other metals,

as arsenic greatly exceeds sulphur in gravity. Some tin ores contain

also a little iron. The ores of tin are to be washed, roasted, and

smelted with a reducing flux, according to the general rules.

_Of Lead Ores._

Lead, like tin, is never found but in a mineral state. It is most

commonly mineralized by sulphur; yet there are some lead ores which

also contain arsenic.

Lead ores, as well as others, must be roasted and smelted with a

reducing flux: however, as it is difficult to free them from all their

sulphur by torrefaction only, the reducing flux employed in their

fusion may be made up with a quantity of iron filings, which being

incapable of any union with lead, and having a much greater affinity

than that metal with sulphur, will, on this occasion, be of great

service by interposing between them.

_Of Quick-silver Ores._

Running Mercury is sometimes found in certain earths, or grey, friable

stones; but most commonly in a mineral state. It is always mineralized

by sulphur, and by sulphur alone: so that cinabar is the only ore of

quick-silver that we know of; and a very rich one it is, seeing it

contains six or seven times as much mercury as sulphur.

Roasting can be of no use towards decomposing the ore of mercury, and

separating its sulphur; because mercury being itself very volatile

would be carried off by the fire together with the sulphur. In order,

therefore, to part the two substances of which cinabar consists,

recourse must necessarily be had to some third body, which will unite

with one of them, and by that means separate it from the other. Now

all the metals, except gold, having a greater affinity than mercury

with sulphur, such a body is easily found: any metal but gold may be

employed with success in this decomposition; but as iron hath a greater

affinity with sulphur than any of the rest, and is moreover the only

one that cannot unite with mercury, it must, on account of these two

qualities, be preferred to all the rest.

Fixed alkalis are also well qualified to absorb the sulphur of cinabar.

Cinabar must be decomposed in close vessels, and by the way of

distillation; otherwise the mercury, as soon as it separates from the

sulphur, will be dissipated in vapours and entirely lost.

In this operation it is needless to add either flux or phlogiston;

because the cinabar is decomposed without melting, and the mercury,

though in a mineral state, contains, like gold and silver, all the

phlogiston requisite to secure its metalline properties.

_Of the Ores of Regulus of Antimony._

Regulus of Antimony is always found in a mineral state: it is

mineralized by sulphur; but sometimes, though rarely, it is also

combined with a little arsenic.

When the ore of regulus of antimony is to be decomposed, the first

thing to be done is to expose it to a degree of heat too weak to melt

its earthy and stony parts, but strong enough to fuse its reguline,

together with its sulphureous parts, which by this means are separated

from the earth, and united into one mass, known by the name of Antimony.

It is plain that this first operation, which is founded on the great

fusibility of antimony, produces, with regard to the ore of regulus

of antimony, the same effect that washing hath on other ores: so that

after this first fusion nothing more is requisite to the obtaining of

a pure regulus of antimony, but to separate it from its sulphur by

roasting, and to melt it with some matter abounding in phlogiston,

in the same manner as other metallic matters are treated. The term

_Calcination_ is generally used to express this torrefaction of

antimony, by means whereof the metallic earth of the regulus of

antimony is separated from its sulphur.

As regulus of Antimony hath, like Mercury, much less affinity with

sulphur than the other metals have, it follows that antimony may be

decomposed by the same means as cinabar; but the regulus, so obtained,

is adulterated with a portion of the additament made use of, which

combines therewith.

There is still another process employed for obtaining the regulus of

antimony: it consists, as was mentioned in its place, in detonating

the mineral with a mixture of nitre and tartar, applied in such a

proportion that, after the detonation has consumed the sulphur, there

may remain so much inflammable matter as will be sufficient to furnish

the metalline earth of the antimony with the phlogiston necessary to

preserve its metallic properties. But by this method less regulus is

produced, than by calcining, or torrefying, and reducing as usual.

_Of the Ores of Bismuth._

The ore of Bismuth consists of the semi-metal mineralized by arsenic,

and of an unmetallic earth. It is very easy to decompose this ore,

and to extract the bismuth it contains: for this purpose it need only

be exposed to a moderate heat, whereby the arsenic will be dissipated

in vapours, and the bismuth melted, which will then separate from the

unmetallic earth. This earth, at least, in several ores of bismuth,

possesses the property of tinging all vitrifiable matters, with which

it is melted, of a beautiful blue colour.

To decompose the ore of bismuth no flux or inflammable matter is used;

because this semi-metal is possessed, even in its mineral state, of

all the phlogiston requisite to maintain its metalline properties; and

its great fusibility makes it unnecessary to melt the unmetallic earth

contained in its ore.

_Of the Ores of Zinc._

Zinc is not generally obtained from a particular ore of its own; but

sublimes during the fusion of a mineral, or rather a confused mass of

minerals, that contains this semi-metal together with iron, copper,

lead, sulphur, arsenic, and, like all other ores, an unmetallic earth.

Nevertheless, there is a substance which may be considered as the

proper ore of zinc, because it contains a pretty large quantity of

that semi-metal, a little iron, and an unmetallic earth. It is called

_Calamine_, or _Lapis Calaminaris_; but hitherto the art of procuring

zinc directly from this mineral hath no where been practised. Calamine

is commonly employed only to convert copper into brass, or a yellow

metal, by cementing it therewith. Indeed, till lately, no easy or

practicable method of obtaining pure zinc from calamine was publicly

known; for that semi-metal being volatile and very inflammable, its ore

cannot be fused like others. Mr. Margraaf was the first who, by mixing

powdered charcoal with calamine in close vessels, obtained a perfect

zinc from it, by the means of distillation or sublimation, as shall be

shewn in our Practical Chymistry.

_Of Arsenical Minerals._

Arsenic, as well as sulphur, is naturally combined with almost all

ores, or minerals containing metallic substances. As it is very

volatile, while the matters with which it is united are fixed, at least

in comparison therewith, it is easily separated by sublimation.

The minerals that contain most arsenic are the white pyrites, orpiment,

and cobalt. We have already considered the white pyrites: as to

orpiment, it consists of sulphur and arsenic. Both these substances

being very volatile, it is difficult to separate them by sublimation:

yet, with proper management, and a due regulation of the fire, this

separation may be effected; because sulphur sublimes a little more

easily than arsenic. But it is more convenient, as well as more

expeditious, to make use of some additament that hath a greater

affinity with one of those substances than with the other. Fixed

alkalis and mercury, both of which have more affinity with sulphur than

with arsenic, may be very properly employed on this occasion.

Cobalt is a mineral composed of arsenic, an unmetallic earth, and

frequently bismuth: and as none of these are very volatile, except the

arsenic, this may be easily separated from the rest by sublimation. The

unmetallic earth which remains has, like that of the ore of bismuth,

the property of giving a blue colour to any vitrifiable matters

melted with it; whence it is conjectured, that cobalt and the ore

of bismuth have a great resemblance, or are often blended with each

other. Nevertheless, Mr. Brant, an ingenious Swedish Chymist, insists

that they are very different: he pretends that the metallic substance

contained in the true cobalt is a semi-metal of a peculiar nature,

which hath been erroneously confounded with bismuth: and indeed he

proves by a great number of curious experiments, related in the Memoirs

of the Academy of Upsal, that these two metallic substances have

properties that are essentially different: to that which is obtained

from cobalt, he gives the name of _Regulus of Cobalt_.

Besides the minerals already recited, there is found in the bowels of

the earth another species of compound body, of which we have already

taken notice; but which is supposed, with some degree of probability,

to belong as much to the vegetable as to the mineral kingdom: I mean

the _Bitumens_; which the best observations oblige us to consider as

vegetable oils, that by lying long in the earth have contracted an

union with the mineral acids, and by that means acquired the thickness,

consistence, and other properties observable in them.

By distillation they yield an oil, and an acid not unlike a mineral

acid. Mr. Bourdelin has even demonstrated, by a very artful and

ingenious process, that amber contains a manifest acid of sea-salt. See

the Memoirs of the Royal Academy of Sciences.

CHAP. XVII.

_Explanation of the Table of Affinities_.

It hath been shewn in the course of this work, that the causes of

almost all the phenomena, which Chymistry exhibits, are deducible from

the mutual affinities of different substances, especially the simplest.

We have already explained (Chap. II.) what is meant by affinities, and

have laid down the principal laws to which the relations of different

bodies are subject. The late Mr. Geoffroy, one of the best Chymists we

have had, being convinced of the advantages which all who cultivate

Chymistry would receive from having constantly before their eyes a

state of the best ascertained relations between the chief agents in

Chymistry, was the first who undertook to reduce them into order, and

unite them all in one point of view, by means of a table. We are of

opinion, with that great man, that this Table will be of considerable

use to such as are beginning to study Chymistry, in helping them to

form a just idea of the relations which different substances have with

one another; and that the practical Chymist will thereby be enabled

to account for what passes in several of his operations, otherwise

difficult to be understood, as well as to judge what may be expected to

result from mixtures of different compounds. These reasons have induced

us to insert it at the end of this Elementary Treatise, and to give a

short explanation of it here; especially as it will serve, at the same

time, for a recapitulation of the whole work, in which the several

axioms of this Table are dispersed.

You have it here just as it was drawn up by Mr. Geoffroy, without any

addition or alteration. I own, however, that it might be improved

both ways: for since the death of that great Chymist many experiments

have been made, some of which have discovered new affinities, and

others have raised exceptions to some of those laid down by him. But

several reasons dissuade me from publishing a new Table of Affinities,

containing all the emendations and innovations that might be made in

the old one.

The first is, that many of the affinities lately discovered are not yet

sufficiently verified, but, on the contrary, subject to be contested:

in short, they are perhaps liable to more considerable objections, and

exceptions, than the other.

The second is, that as Mr. Geoffroy's Table contains all the

fundamental affinities, it is more suitable to an Elementary Treatise

than a much fuller one would be; seeing this would necessarily suppose

the knowledge of many things not treated of by us, and of which it was

not proper to say any thing in such a book as this.

However, as it is essential to our purpose that we lead none into

error, we shall take care in explaining the affinities delivered by Mr.

Geoffroy, to mention the principal objections and exceptions to which

they are liable: we shall, moreover, add a very few new ones, confining

ourselves to such only as are elementary and well ascertained.

The upper line of Mr. Geoffroy's Table, comprehends several substances

used in Chymistry. Under each of those substances are ranged in

distinct columns several matters compared with them, in the order

of their relation to that first substance; so as that which is the

nearest to it is that which hath the greatest affinity with it, or that

which none of the substances standing below it can separate therefrom;

but which, on the contrary, separates them all when they are combined

with it, and expels them in order to join itself therewith. The same is

to be understood of that which occupies the second place of affinity;

that is, it has the same property with regard to all below it, yielding

only to that which is above it: and so of all the rest.

At the top of the first column stands the character which denotes an

Acid in general. Immediately under this stands the mark of a Fixed

Alkali, being placed there as the substance which has the greatest

affinity with an Acid. After the Fixed Alkali appears the Volatile

Alkali, whose affinity with Acids yields only to the Fixed Alkali.

Next come the Absorbent Earths; and last of all Metallic Substances.

Hence it follows, that when a Fixed Alkali is united with an acid it

cannot be separated therefrom by any other substance; that a Volatile

Alkali united with an Acid cannot be separated from it by any thing

but a Fixed Alkali; that an Absorbent Earth combined with an acid

may be separated from it either by a Fixed or by a Volatile Alkali;

and lastly, that any Metallic Substance combined with an Acid may be

separated from it by a Fixed Alkali, a Volatile Alkali, or an Absorbent

Earth.

There are many important remarks to be made on this first column.

First, it is making the rule too general to say that any Acid whatever

has a greater affinity with a Fixed Alkali, than with any other

substance. And indeed Mr. Geoffroy himself hath made an exception

with respect to the Vitriolic Acid; for in the fourth column, at the

head of which stands that Acid, we find the sign of the Phlogiston

placed above that of the Fixed Alkali, as having a greater affinity

than the Fixed Alkali with the Vitriolic Acid. This is founded on the

famous experiment, wherein Vitriolated Tartar and Glauber's Salt are

decompounded by means of the Phlogiston, which separates the Fixed

Alkalis of these Neutral Salts, and uniting with the Vitriolic Acid

contained in them forms therewith a Sulphur.

Secondly, Nitre deflagrates, and is decomposed, by the contact of any

inflammable matter whatever that is actually ignited; and the operation

which produces Phosphorus is no other than a decomposition of sea-salt,

whose Acid quits its Alkaline basis to join with the Phlogiston: now

these facts furnish very strong reasons for believing that both these

Acids, as well as the Vitriolic, have a stronger affinity with the

Phlogiston than with a Fixed Alkali. Lastly, as several experiments

shew the Vegetable Acids to be only the Mineral Acids disguised and

mortified, there are sufficient grounds for suspecting that Acids in

general have a greater affinity with the Phlogiston than with Fixed

Alkalis: so that instead of making an exception with regard to the

Vitriolic Acid, it would perhaps be better to lay down this greater

affinity as common to all Acids whatever, and to place the Phlogiston

in the first column, immediately under the character which denotes an

Acid in general. This theory, however, stands in need of confirmation

from other experiments[4].

[4] Mr. Margraaf, an able German Chymist, has made several

experiments, which induce him to think that the Acid of Phosphorus

is of a particular kind, and different from that of sea-salt. May it

not be the Marine Acid, but altered by the union it has contracted

with the Phlogiston? Or may it not be, with respect to Phosphorus,

what the volatile sulphureous spirit is, with respect to Sulphur?

See the Memoirs of the Royal Academy of Sciences of Berlin.

Thirdly, in this same column the character of a Volatile Alkali is set

above that of an Absorbent Earth, as having a greater affinity with

Acids; and yet these Absorbent Earths decompose the Ammoniacal salts,

drive away the Volatile Alkali from the Acids, and assume its place.

This is one of the first objections made against Mr. Geoffroy's Table.

His answer thereto is printed in the Memoirs of the Academy of Sciences

for 1718, where his Table also is to be found. We have already declared

our opinion about this matter in treating of a Volatile Alkali.

Fourthly, in 1744, Mr. Geoffroy, brother to the author of the Table,

who hath done no less honour to Chymistry than that eminent physician,

gave in a Memoir containing an exception to the last affinity in the

first column; namely, that which places Absorbent Earths above Metallic

substances. He therein shews, that Alum may be converted into Copperas

by boiling it in iron vessels; that, on this occasion, the iron

precipitates the Earth of the Alum, separates it from its Acid, and

assumes its place; so that of course it must have a greater affinity,

than the Absorbent Earth of Alum, with the Vitriolic Acid.

At the head of the second column stands the character of the Marine

Acid, which signifies that the affinities of this Acid are the subject

of the column. Immediately below it is placed the mark of Tin. As this

is a metalline substance, and as the first column places metalline

substances in the lowest degree of affinity with all Acids, it is

plain we must suppose Fixed Alkalis, Volatile Alkalis, and Absorbent

Earths, to be placed here in order after the Marine Acid, and before

Tin. Tin, then, is of all Metalline substances that which has the

greatest affinity with the Marine Acid; and then follow Regulus of

Antimony, Copper, Silver, Mercury. Gold comes last of all; and there

are no less than two vacant places above it. By this means it is in

some sort excluded from the rank of substances that have an affinity

with the Marine Acid. The reason thereof is, that this Acid alone is

not capable of dissolving Gold and combining therewith, necessarily

requiring for that purpose the aid of the Nitrous Acid, or at least of

the Phlogiston.

The third column exhibits the affinities of the Nitrous Acid, the

character whereof stands at its head. Immediately below it is the sign

of Iron, as the metal which has the greatest affinity with this Acid;

and then follow other metals, each according to the degree of its

relation; to wit, Copper, Lead, Mercury, and Silver. In this column,

as in the preceding one, we must suppose the substances, which in the

first column stand above Metallic substances, to be placed in their

proper order before Iron.

The fourth column is intended to represent the Affinities of the

Vitriolic Acid. Here Mr. Geoffroy has placed the Phlogiston as the

substance which has the greatest affinity with this Acid, for the

reason given in our explanation of the first column. Below it he has

ranked Fixed Alkalis, Volatile Alkalis, and Absorbent Earths, to

shew that this is an exception to the first column. As to Metalline

substances, he has set down but three, being those with which the

Vitriolic Acid has the most perceptible affinity: these metals, placed

in the order of their affinities, are Iron, Copper, and Silver.

The fifth column shews the affinities of Absorbent Earths. As these

Earths have no sensible affinity but with Acids, this column contains

only the characters of the Acids ranked according to the degree of

their strength, or affinity with the Earths; to wit, the Vitriolic, the

Nitrous, and the Marine Acids. Underneath this last might be placed the

Acid of Vinegar, or the Vegetable Acid.

The sixth column expresses the Affinities of Fixed Alkalis with Acids,

which are the same with those of Absorbent Earths. Moreover, we find

Sulphur placed here below all the Acids; because Liver of Sulphur,

which is a combination of Sulphur with a Fixed Alkali, is actually

decompounded by any Acid: for any Acid precipitates the Sulphur and

unites with the Alkali.

Immediately over the Sulphur, or in the same square with it, might be

set a mark denoting the Volatile Sulphureous Spirit; because, like

Sulphur, it has less affinity than any other Acid with Fixed Alkalis.

Oils might also be ranked with Sulphur, because they unite with Fixed

Alkalis, and therewith form Soaps, which are decompounded by any acid

whatever.

The seventh column points out the affinities of Volatile Alkalis, which

are likewise the same as those of Absorbent Earths; and the Vegetable

Acid might be placed here also under the Marine Acid.

The eighth column specifies the affinities of Metallic substances

with Acids. The affinities of the Acids, which, with respect to Fixed

Alkalis, Volatile Alkalis, and Absorbent Earths, succeeded each other

uniformly, do not appear in the same order here. The Marine Acid,

instead of being placed below the Vitriolic and Nitrous Acids, stands,

on the contrary, at their head; because, in fact, this Acid separates

Metalline substances from all the other Acids with which they happen

to be united, and, forcing these Acids to quit possession, intrudes

into their place. Nevertheless, this is not a general rule; for several

Metalline substances must be excepted, particularly Iron and Copper.

The ninth column declares the affinities of Sulphur. Fixed Alkalis,

Iron, Copper, Lead, Silver, Regulus of Antimony, Mercury, and Gold,

stand below it in the order of their affinities. With regard to Gold it

must be observed, that it will not unite with pure Sulphur: it suffers

itself to be dissolved only by the Liver of Sulphur, which is known to

be a composition of Sulphur and Fixed Alkali.

At the head of the tenth column appears Mercury, and beneath it several

Metalline substances, in the order of their affinities with it. Those

Metalline substances are Gold, Silver, Lead, Copper, Zinc, and Regulus

of Antimony.

It is proper to remark on this column, that Regulus of Antimony,

which stands the lowest, unites but very imperfectly with Mercury;

and that after a seeming union of these two Metallic substances hath

been obtained, by a tedious triture with the addition of water, they

do not continue long united, but spontaneously separate from each

other in a short time. Iron and Tin are here excluded; the former

with great reason, because hitherto it hath not been clearly proved,

by any known experiment, that ever Mercury was united with Iron: but

the same objection cannot be made to Tin, which amalgamates very well

with Mercury, and might therefore be placed in this column nearly

between Lead and Copper. I use the word _nearly_, because the different

degrees of affinity between Metalline substances and Mercury are not so

exactly determined, as the other relations before considered; seeing

they generally unite with it, without excluding one another. We can

therefore scarce judge of the degree of affinity that belongs to each,

but by the greater or less readiness of each to amalgamate therewith.

The eleventh column shews, that Lead has a greater affinity with Silver

than with Copper.

The twelfth, that Copper has a greater affinity with Mercury than with

Calamine.

The thirteenth, that Silver has a greater affinity with Lead than with

Copper.

The fourteenth contains the affinities of Iron. Regulus of Antimony

stands immediately underneath it, as being the Metallic substance which

has the greatest affinity with it. Silver, Copper, and Lead, are placed

together in the next square below, because the degrees of affinity

which those metals have with Iron are not exactly determined.

The same is to be said of the fifteenth column: Regulus of Antimony

stands at its head; Iron is immediately below it; and below the Iron

the same three metals occupy one square as before.

Lastly, the sixteenth column indicates that Water has a greater

affinity with Spirit of Wine than with Salts. By this general

expression must not be understood any Saline substance whatever; but

only the Neutral Salts, which Spirit of Wine frees from the water that

kept them in solution. Fixed Alkalis, on the contrary, as well as the

Mineral Acids, have a greater affinity than Spirit of Wine with water:

so that these Saline substances, being well dephlegmated, and mixed

with Spirit of Wine; imbibe the water it contains and rectify it.

To these might be added another short column, having Spirit of Wine at

its head: immediately below it should be the character of Water, and

below that the mark of Oil. This column would shew that the Spirit of

Wine has a greater affinity with Water than with Oils; because any Oily

matter whatever, that is dissolved in Spirit of Wine, may be actually

separated from it by the affusion of Water. This rule admits of no

exception but in one case; which is when the oily substance partakes

of the nature of soap, by having contracted an union with some saline

matter. But as this must be imputed wholly to that adventitious saline

matter being superadded to the oily substance, it is no just foundation

for an exception, and the affinity in question is nevertheless general.

We have now delivered every thing material that we had to say

concerning Mr. Geoffroy's Table of Affinities. It is, as we observed

before, of exceeding great service, as it collects into one view

the principal truths laid down in this Treatise. Indeed the most

advantageous way of using it is, not to delay consulting it till you

have read the book through, but to turn to it while you are reading, as

oft as any affinity between bodies is treated of; which it will imprint

more strongly on your mind, by representing it in a manner before your

eyes.

CHAP. XVIII.

_The_ THEORY _of_ CONSTRUCTING _the_ VESSELS _most commonly used in_

CHYMISTRY.

Chymists cannot perform the operations of their art without the help of

a considerable number of vessels, instruments, and furnaces, adapted

to contain the bodies on which they intend to work, and to apply to

them the several degrees of heat required by different processes. It is

therefore proper, before we advance to the operations themselves, to

consider particularly and minutely what relates to the instruments with

which they are to be performed.

Vessels intended for Chymical Operations should, to be perfect, be

able to bear, without breaking, the sudden application of great heat

and great cold; be impenetrable to every thing, and unalterable by any

solvent; unvitrifiable, and capable of enduring the most violent fire

without melting: but hitherto no vessels have been found with all these

qualities united.

They are made of sundry materials; namely, of metal, of glass, and of

earth. Metalline vessels, especially those made of Iron or Copper,

are apt to be corroded by almost every saline, oily, or even aqueous

substance. For this reason, in order to render the use of them a little

more extensive, they are tinned on the inside. But, notwithstanding

this precaution, they are on many occasions not to be trusted; and

should never be employed in any nice operations which require great

accuracy: they are, moreover, incapable of resisting the force of fire.

Earthen vessels are of several sorts. Some, that are made of a

refractory earth, are capable of being suddenly exposed to a strong

fire without breaking, and even of sustaining a great degree of heat

for a considerable time: but they generally suffer the vapours of

the matters which they contain, as well as vitrified metals, to pass

through them, especially the glass of lead, which easily penetrates

them and runs through their pores as through a sieve. There are others

made of an earth that, when well baked, looks as if it were half

vitrified: these being much less porous, are capable of retaining the

vapours of the matters which they contain, and even glass of lead in

fusion; which is one of the severest trials a vessel can be put to: but

then they are more brittle than the other sort.

Good glass vessels should constantly be employed in preference to all

others, whenever they can possibly be used: and that not only because

they are no way injured by the most active solvents, nor suffer any

part of what they contain to pass through, but also because their

transparency allows the Chymist to observe what passes within them:

which is always both curious and useful. But it is pity that vessels of

this sort should not be able to endure a fierce fire without melting.

We shall take care, when we come to describe the several sorts of

chymical instruments, and the manner of using them, to note what

vessels are to be preferred to others on different occasions.

Distillation, as hath been already said, is an operation by which

we separate from a body, by the help of a gradual heat, the several

principles of which it consists.

There are three methods of distilling. The first is performed by

applying the heat over the body whose principles are to be extracted.

In this case, as the liquors, when heated and converted into vapours,

constantly endeavour to fly from the center of heat, they are forced to

re-unite in the lower part of the vessel, that contains the matter in

distillation, and so passing through the pores or holes of that vessel,

they fall into another cold vessel applied underneath to receive them.

This way of distilling is on this account called distilling _per

Descensum_. It requires no other apparatus than two vessels figured

like segments of hollow spheres, whereof that which is pierced with

little holes, and intended to contain the matter to be distilled,

should be much less than the other, which is to contain the fire,

and to fill its aperture exactly; the whole together to be supported

vertically upon a third vessel, which is to serve the purpose of a

recipient, admitting into its mouth the convex bottom of the vessel

containing the matter to be distilled, which must accurately fill it.

This method of distilling is but little used.

The second method of distilling is performed by applying the heat

underneath the matter to be decomposed. On this occasion the liquors

being heated, rarefied, and converted into vapours, rise, and are

condensed in a vessel contrived for that purpose, which we shall

presently describe. This way of distilling is called distilling _per

Ascensum_, and is much used.

The vessel in which this distillation _per Ascensum_ is performed we

call an _Alembic_.

There are several sorts thereof, differing from one another both in the

matter of which, and the manner in which, they are made.

Those employed to draw the odoriferous waters and essential oils of

plants are generally made of copper, and consist of several pieces. The

first, which is designed to contain the plant, is formed nearly like a

hollow cone, the vertex whereof is drawn out in the shape of a hollow

cylinder or tube: this part is named the _Cucurbit_, and its tube the

_Neck_ of the _Alembic_. To the upper end of this tube another vessel

is soldered: this is called the _Head_, and commonly has likewise the

form of a cone, joined to the neck of the alembic by its base, round

which, on the inside, is hollowed a small groove, communicating with

an orifice that opens at its most depending part. To this orifice is

soldered a small pipe in a direction sloping downwards, which is called

the _Nose_, _Spout_, or _Beak_ of the alembic.

As soon as the matters contained in the alembic grow hot, vapours begin

to arise from them, and ascending through the neck of the alembic into

the head, are by the sides thereof stopped and condensed: from thence

they trickle down in little streams to the groove, which conveys them

to the spout; and by that they pass out of the alembic into a glass

vessel with a long neck, the end of the spout being introduced into

that neck, and luted thereto.

To facilitate the refrigeration and condensation of the vapours

circulating in the head, all alembics of metal are moreover provided

with another piece, which is a kind of large pan of the same metal,

fitted and soldered round the head. This piece serves to keep cold

water in, which incessantly cools the head, and therefore it is called

the _Refrigeratory_. The water in the refrigeratory itself grows hot

after some time, and must therefore be changed occasionally; the heated

water being first drawn off by means of a cock fixed near the bottom of

the refrigeratory. All copper alembics should be tinned on the inside

for the reasons already given.

When saline spirits are to be distilled, alembics of metal must not

be used; because the saline vapours would corrode them. In this case

recourse must be had to alembics of glass. These consist of two pieces

only; namely, a _Cucurbit_, whose superior orifice is admitted into and

exactly luted with its _Head_, which is the second piece.

In general, as alembics require that the vapours of the matter to be

distilled should rise to a considerable heighth, they ought to be used

only when the most volatile principles are to be drawn from bodies:

and the lighter and more volatile the substances to be separated by

distillation are, the taller must the alembic be; because the most

ponderous parts, being unable to rise above a certain heighth, fall

back again into the cucurbit as soon as they arrive there, leaving the

lighter to mount alone, whose volatility qualifies them to ascend into

the head.

When a matter is to be distilled, that requires a very tall alembic,

and yet does not admit of a metalline vessel, the end will be best

answered by a glass vessel of a round or oval shape, having a very

long neck, with a small head fitted to its extremity. Such a vessel

serves many purposes: it is sometimes employed as a receiver, and at

other times as a digesting vessel; on which last occasion it goes under

the name of a _Matrass_. When one of these, provided with a head, is

applied to the purpose of distilling, it forms a sort of alembic.

There are some alembics of glass, blown in such a manner by the

workmen, that the body and head form but one continued piece. As these

alembics do not stand in need of having their several pieces luted

together, they are very useful on some occasions, when such exceeding

subtile vapours rise as are capable of transpiring through lutes. The

head must have an aperture at the top, provided with a short tube,

through which, by means of a funnel with a long pipe, the matter to be

distilled may be introduced into the cucurbit. This is to be exactly

closed with a glass stopple, the surface whereof must be made to fit

the inside of the tube in every point, by rubbing those two pieces

well together with emery.

Another sort of alembic hath also been invented, which may be used

with advantage when _Cohobation_ is required; that is, when the liquor

obtained by distillation is to be returned upon the matter in the

cucurbit; and especially when it is intended that this cohobation

shall be repeated a great number of times. The vessel we are speaking

of is constructed exactly in the same manner as that last described;

except that its beak, instead of being in a straight line, as in the

other alembics, forms a circular arch, and re-enters the cavity of the

cucurbit, in order to convey back again the liquor collected in the

head. This instrument hath commonly two beaks opposite to each other,

both turned in this manner, and is called a _Pelican_: it saves the

artist the trouble of frequently unluting and reluting his vessels, as

well as the loss of a great many vapours.

There are certain substances which in distillation afford matters in

a concrete form, or rise wholly in the form of a very light powder,

called _Flowers_. When such substances are to be distilled, the

cucurbit which contains them is covered with a head without a nose,

which is named a _Blind-head_.

When the flowers rise in great quantities and very high, a number of

heads is employed to collect them; or rather a number of a kind of

pots, consisting of a body only without any bottom, which fitting one

into the other form a canal, that may be lengthened or shortened at

pleasure, according as the flowers to be sublimed are more or less

volatile. The last of the heads, which terminates the canal, is quite

close at one end, and makes a true blind-head. These vessels are called

_Aludels_; they are usually of earthen or stone ware.

All the vessels above-mentioned are fit only for distilling such light

volatile matters as can be easily raised and brought over; such as

phlegm, essential oils, fragrant waters, acid oily spirits, volatile

alkalis, _&c._ But when the point is to procure by distillation

principles that are much less volatile, and incapable of rising high,

such as the thick fetid oils, the vitriolic, the nitrous, and the

marine acids, _&c._ we are under a necessity of having recourse to

other vessels, and another manner of distilling.

It is easy to imagine, that such a vessel must be much lower than

the alembic. It is indeed no more than a hollow globe, whose upper

part degenerates into a neck or tube, that is bent into a horizontal

position; for which reason this instrument is called a _Retort_: it is

always of one single piece.

The matter to be distilled is introduced into the body of the retort by

means of a ladle with a long tubular shank. Then it is set in a furnace

built purposely for this use, and so that the neck of the retort coming

out of the furnace may, like the nose of the alembic, stand in a

sloping position, to facilitate the egress of the liquors, which by its

means are conveyed to a receiver, into which it is introduced, and with

which it is luted. This way of distilling, in which the vapours seem

rather to be driven out of the vessel horizontally and laterally, than

raised up and sublimed, is for that reason called Distillation _per

Latus_.

Retorts are, of all the instruments of distillation, those that must

sustain the greatest heat, and resist the strongest solvents; and

therefore they must not be made of metal. Some, however, which are

made of iron may do well enough on certain occasions: the rest are

either of glass or earth. Those of glass, for the reasons above given,

are preferable to the other sort, in all cases where they are not to

be exposed to such a force of fire as may melt them. The best glass,

that which stands both heat and solvents best, is that in which there

are fewest alkaline salts. Of this sort is the green German glass: the

beautiful white crystal glass is far from being equally serviceable.

Retorts, as well as alembics, may be of different forms. For example,

some matters are apt to swell, and rise over the neck of the retort in

substance, without suffering any decomposition; when such matters are

to be distilled in a retort, it is proper that the body of the vessel,

instead of being globular, be drawn out into the form of a pear, so as

nearly to resemble that of a cucurbit. In a retort of this kind, the

distance between the bottom and the neck being much greater than in

those whose bodies are spherical, the matters contained have much more

room for expansion; so that the inconvenience here mentioned is thereby

prevented. Retorts of this form are called English retorts. As they

hold the middle place between alembics and common retorts, they may be

used to distil such matters as have a mean degree of volatility between

the greatest and the least.

It is moreover proper to have, in a laboratory, sundry retorts with

necks of different diameters. Wide necks will be found the fittest

for conveying thick matters, and such as readily become fixed; for

instance, some very thick fetid oils, butter of antimony, _&c._; for

as these matters acquire a consistence as soon as they are out of

the reach of a certain degree of heat, they would soon choak a narrow

neck, and by stopping the vapours which rise at the same time from the

retort, might occasion the bursting of the vessels.

Some retorts are also made with an opening on their upper side, like

that of tubulated glass alembics, which is to be closed in the same

manner with a glass stopple. These retorts are also called Tubulated

retorts, and ought always to be used whenever it is necessary to

introduce fresh matter into the retort during the operation; seeing it

may be done by means of this invention, without unluting and reluting

the vessels; which ought always to be avoided as much as possible.

One of the things that most perplexes the Chymists, is the prodigious

elasticity of many different vapours, which are frequently discharged

with impetuosity during the distillation, and are even capable of

bursting the vessels with explosion, and with danger to the artist. On

such occasions it is absolutely necessary to give these vapours vent,

as we shall direct in its proper place: but as that can never be done

without losing a great many of them; as some of them in particular

are so elastic that scarce any at all would remain in the vessel; for

instance, those of the spirit of nitre, and especially those of the

smoking spirit of salt; the practice is to make use of very large

receivers, of about eighteen or twenty inches diameter, that the

vapours may have sufficient room to circulate in, and by applying to

the wide surface presented them by the extensive inside of such a large

vessel, may be condensed into drops. These huge receivers are commonly

in the form of hollow globes, and are called Ballons.

To give these vapours still more room, ballons have been contrived

with two open gullets in each, diametrically opposite to one another;

whereof one admits the neck of the retort, and the other is received by

one of the gullets of a second ballon of the same form, which is joined

in like manner to a third, and so on. By this artifice the space may be

enlarged at pleasure. These ballons with two necks are called Adopters.

Operations on bodies that are absolutely fixed, as metals, stones,

sand, _&c._ require only such vessels as are capable of containing

those bodies, and resisting the force of fire. These vessels are little

hollow pots, of different dimensions, which are called Crucibles.

Crucibles can hardly be made of any thing but earth; they ought to have

a cover of the same material fitted to shut them close. The best earth

we know is that whereof those pots are made in which butter is brought

from Bretagne: these pots themselves are exceeding good crucibles; and

they are almost the only ones that are capable of holding glass of lead

in fusion, without being penetrated by it.

For the roasting of ores, that is, freeing them, by the help of fire,

from their sulphureous and arsenical parts, little cups of the same

material with crucibles are used; but they are made flat, shallow,

and wider, above than below, that these volatile matters may the more

freely exhale. These vessels are called Tests, or Scorifiers: they are

scarce ever used but in the Docimastic art, that is, in making small

Assays of ores.

CHAP. XIX.

_The_ THEORY _of_ CONSTRUCTING _the_ FURNACES _most commonly used in_

CHYMISTRY.

Skill in conducting and applying fire properly, and determining its

different degrees, is of very great consequence to the success of

Chymical operations.

As it is exceeding difficult to govern and moderate the action of fire,

when the vessels in which any operation is performed are immediately

exposed to it, Chymists have contrived to convey heat to their vessels,

in nice operations, through different mediums, which they place

occasionally between those vessels and the fire.

Those intermediate substances in which they plunge their vessels are

called Baths. They are either fluid or solid: the fluid baths are water

or its vapours. When the distilling vessel is set in water, the bath is

called _Balneum Mariæ_, or the _Water Bath_; and the greatest degree

of heat of which it is susceptible is that of boiling water. When the

vessel is exposed only to the vapours which exhale from water, this

forms the _Vapour Bath_; the heat of which is nearly the same with

that of the _Balneum Mariæ_. These baths are useful for distilling

essential oils, ardent spirits, sweet-scented waters; in a word, all

such substances as cannot bear a greater heat, without prejudice either

to their odour, or to some of their other qualities.

Baths may also be made of any other fluids, such as oils, mercury,

_&c._ which are capable of receiving and communicating much more heat:

but they are very seldom used. When a more considerable degree of

heat is required, a bath is prepared of any solid matter reduced to a

fine powder, such as sand, ashes, filings of iron, _&c._ The heat of

these baths may be pushed so far as to make the bottom of the vessel

become faintly red. By plunging a thermometer into the bath, by the

side of the vessel, it is easy to observe the precise degree of heat

applied to the substance on which you are working. It is necessary

that the thermometers employed on this occasion be constructed on good

principles, and so contrived as to be easily compared with those of the

most celebrated natural philosophers. Those of the illustrious Réaumur

are most used and best known, so that it would not be amiss to give

them the preference. When a greater heat is required than any of those

baths can give, the vessels must be set immediately on live coals, or

in a flaming fire: this is called working with a naked fire; and, in

this case it is much more difficult than in the other to determine the

degrees of heat.

There are several ways of applying a naked fire. When the heat or flame

is reflected upon the upper part of a vessel which is exposed to the

fire, this is called a Reverberated heat. A Melting heat is that which

is strong enough to fuse most bodies. A Forging heat is that of a fire

which is forcibly excited by the constant blast of a pair of bellows,

or more.

There is also another sort of fire which serves very commodiously for

many operations, because it does not require to be fed or frequently

mended: this is afforded by a lamp with one or more wicks, and may be

called a Lamp-heat. It is scarce ever employed but to heat baths, in

operations which require a gentle and long continued warmth: if it hath

any fault, it is that of growing gradually hotter.

All the different ways of applying fire require Furnaces of different

constructions: we shall therefore describe such as are of principal and

most necessary use.

Furnaces must be divided into different parts or stories, each of which

has its particular use and name.

The lower part of the furnace, designed for receiving the ashes and

giving passage to the air, is called the Ash-hole. The ash-hole is

terminated above by a grate, the use of which is to support the coals

and wood, which are to be burnt thereon: this part is called the

Fire-place. The fire-place is in like manner terminated above by

several iron bars, which lie quite across it from right to left, in

lines parallel to each other: the use of these bars is to sustain the

vessels in which the operations are to be performed. The space above

these bars to the top of the furnace is the upper story, and may be

called the Laboratory of the furnace. Lastly, some furnaces are quite

covered above by means of a kind of vaulted roof called the Dome.

Furnaces have moreover several apertures: one of these is at the

ash-hole, which gives passage to the air, and through which the ashes

that fall through the grate are raked out; this aperture is called the

ash-hole Door: another is at the fire-place, through which the fire

is supplied with fuel, as occasion requires; this is called the mouth

or door of the Fire-place, or the Stoke-hole: there is a third in the

upper story, through which the neck of the vessel passes; and a fourth

in the dome for carrying off the fuliginosities of combustible matters,

which is called the Chimney.

To conclude, there are several other openings in the several parts of

the furnace, the use whereof is to admit the air into those places, and

also, as they can be easily shut, to incite or slacken the activity of

the fire, and so to regulate it; which has procured them the title of

Registers. All the other openings of the furnace should be made to shut

very close, the better to assist in governing the fire; by which means

they likewise do the office of registers.

In order to our forming a just and general idea of the construction of

furnaces, and of the disposition of the several apertures in them, with

a view to increase or diminish the activity of the fire, it will be

proper to lay down, as our ground-work, certain principles of natural

philosophy, the truth of which is demonstrated by experience.

And first, every body knows that combustible matters will not burn or

consume unless they have a free communication with the air; insomuch

that if they be deprived thereof, even when burning most rapidly, they

will be extinguished at once: that consequently combustion is greatly

promoted by the frequent accession of fresh air, and that a stream of

air, directed so as to pass with impetuosity through burning fuel,

excites the fire to the greatest possible activity.

Secondly, it is certain that the air which touches, or comes near

ignited bodies is heated, rarefied, and rendered lighter than the

air about it, that is, farther distant from the center of heat;

and consequently that this air, so heated and become lighter, is

necessarily determined thereby to ascend and mount aloft, in order

to make room for that which is less heated and not so light, which by

its weight and elasticity tends to occupy the place quitted by the

other. Another consequence hereof is, that if fire be kindled in a

place enclosed every where but above and below, a current of air will

be formed in that place, running in a direction from the bottom to the

top; so that if any light bodies be applied to the opening below, they

will be carried up towards the fire; but, on the contrary, if they be

held at the opening above, they will be impelled by a force which will

drive them up, and carry them away from the fire.

Thirdly and lastly, it is a truth demonstrated in hydraulics, that the

velocity of a given quantity of any fluid, determined to flow in any

direction whatever, is so much the greater the narrower the channel is

to which that fluid is confined; and consequently that the velocity

of a fluid will be increased by making it run from a wider through a

narrower passage.

These principles being established, it is easy to apply them to the

construction of furnaces. First, if a fire be kindled in the fire-place

of a furnace, which is open on all sides, it burns nearly as if it were

in the open air. It has with the surrounding air a free communication;

so that fresh air is continually admitted to facilitate the entire

combustion of the inflammable matters employed as fuel. But there being

nothing to determine that air to pass with rapidity through the fire in

this case, it does not at all augment the activity thereof, but suffers

it to waste away quietly.

Secondly, if the ash-hole or dome of a furnace, in which a fire

is burning, be shut quite close, then there is no longer any free

communication between the air and the fire: if the ash-hole be shut,

the air is debarred from having free access to the fire; if the dome

be stopt, the egress of the air rarefied by the fire is prevented; and

consequently the fire must in either case burn very faintly and slowly,

gradually die away, and at last go quite out.

Thirdly, if all the openings of the furnace be wholly closed, it is

evident that the fire will be very quickly extinguished.

Fourthly, if only the lateral openings of the fire-place be shut,

leaving the ash-hole and upper part of the furnace open; it is plain

that the air entering by the ash-hole will necessarily be determined

to go out at top, and that consequently a current of air will be

formed, which will pass through the fire, and make it burn briskly and

vigorously.

Fifthly, if both the ash-hole and the upper story of the furnace be

of some length, and form canals either cylindric or prismatic, then

the air being kept in the same direction through a longer space, the

course of its stream will be both stronger and better determined, and

consequently the fire will be more animated by it.

Sixthly and lastly, if the ash-hole and the upper part of the furnace,

instead of being cylindric or prismatic canals, have the form of

truncated cones or pyramids, standing on their bases, and so ordered

that the upper opening of the ash-hole, adjoining to the fire-place,

may be wider than the base of the superiour cone or pyramid, then the

stream of air, being forced to pass incessantly from a larger channel

through a smaller, must be considerably accelerated, and procure to

the fire the greatest activity which it can receive from the make of a

furnace.

The materials fittest for building furnaces are, 1. Bricks, joined

together with potters clay mixed with sand and moistened with water. 2.

Potters clay mingled with potsherds, moistened with water, and baked in

a violent fire. 3. Iron; of which all furnaces may be made, with this

precaution, that the inside be provided with a great many prominent

points, as fastenings for a coat of earth, with which the internal

parts of the furnace must necessarily be covered to defend it from the

action of the fire.

The reverberating furnace is one of those that are most employed in

Chymistry: it is proper for distillations by the retort, and should be

constructed in the following manner.

First, the use of the ash-hole being, as was said, to give passage

to the air and to receive the ashes, no bad consequence can attend

its being made pretty high: it may have from twelve to twenty or

twenty-four inches in heighth. Its aperture should be wide enough to

admit billets of wood, when a great fire is to be made.

Secondly, the ash-hole must be terminated at its upper part by an

iron grate, the bars of which should be very substantial, that they

may resist the action of the fire: this grate is the bottom of the

fire-place, and destined to support the coals. In the lateral part of

the fire-place, and nearly about the same heighth with the grate, there

should be a hole of such a size that it may easily admit charcoal, as

well as little tongs and shovels for managing the fire. This aperture

or mouth of the fire-place should be perpendicularly over the mouth of

the ash-hole.

Thirdly, from six to eight or ten inches high above the grate over the

ash-hole, little apertures must be made in the walls of the furnace,

of eight or ten lines in diameter, an inch from one another, and those

in one side must be diametrically opposite to those in the other. The

use of these holes is to receive bars of iron for the retort to rest

on; which should be, as I said, at different heights, in order to

accommodate retorts of different sizes. At the upper extremity of this

part of the furnace, which reaches from the iron bars to the top, the

heighth whereof should be somewhat less than the width of the furnace,

must be cut a semi-circular aperture for the neck of the retort to come

through. This hole must by no means be over the doors of the fire-place

and ash-hole; for then, as it gives passage to the neck of the retort,

it must of course be opposite to the receiver, and in that case the

receiver itself would stand over against those two apertures; which

would be attended with this double inconvenience, that the receiver

would not only grow very hot, but greatly embarrass the operator, whose

free access to the fire-place and ash-hole would be thereby obstructed.

It is proper therefore that the semi-circular cut we are speaking of be

so placed that when the greatest ballons are luted to the retort they

may leave an open passage to the fire-place and ash-hole.

Fourthly, in order to cover in the laboratory of the reverberating

furnace, there must be a roof made for it in the form of a cupola,

or concave hemisphere, having the same diameter as the furnace. This

dome should have a semi-circular cut in its rim, answering to that

above-directed to be made in the upper extremity of the furnace,

so that, when adjusted to each other, the two together may form a

circular hole for the neck of the retort to pass through. At the top of

this dome there must also be a circular hole of three or four inches

diameter, carrying a short tapering funnel of the same diameter, and

three inches high, which will serve for a chimney to carry off all

fuliginosities, and accelerate the current of the air. This passage may

be shut at pleasure with a flat cover. Moreover, as it is necessary

that the dome should be taken off and put on with ease, it should have

two ears or handles for that purpose: a portative or moveable furnace

should also have a pair of handles, fixed opposite to each other,

between the ash-hole and the fire-place.

Sixthly and lastly, a conical canal must be provided of about three

feet long, and sufficiently wide at its lower end to admit the funnel

of the aperture at the top of the dome. This conical tube is to be

applied to the dome when the fire is required to be extremely active:

it tapers gradually from its base upwards, and breaks off as if

truncated at top, where it should be about two inches wide.

Besides the apertures already mentioned as necessary to a reverberating

furnace, there must also be many other smaller holes made in its

ash-hole, fire-place, laboratory, and dome, which must all be so

contrived as to be easily opened and shut with stopples of earth: these

holes are the registers of the furnace, and serve to regulate the

activity of the fire, according to the principles before laid down.

When the action of the fire is required to be exactly uniform and very

brisk, it is necessary to stop carefully with moist earth all the

little chinks in the juncture of the dome with the furnace, between the

neck of the retort and the circular hole through which it passes, and

which it never fills exactly, and, lastly, the holes which receive the

iron bars that sustain the retort.

It is proper to have, in a laboratory, several reverberating furnaces

of different magnitudes; because, they must be proportioned to the size

of the retorts employed. The retort ought to fill the furnace, so as

to leave only the distance of an inch between it and the inside of the

furnace.

Yet when the retort is to be exposed to a most violent fire, and

especially when it is required that the heat shall act with equal force

on all parts of the furnace, and as strongly on its vault as on its

bottom, a greater distance must be left between the retort and the

inside of the furnace; for then the furnace may be filled with coals,

even to the upper part of the dome. If moreover some pieces of wood be

put into the ash-hole, the conical canal fitted on to the funnel of the

dome, and all the apertures of the furnace exactly closed, except the

ash-hole and the chimney, the greatest heat will then be excited that

this furnace can produce.

The furnace now described may also be employed in many other chymical

operations. If the dome be laid aside, an alembic may very well be

placed therein: but then the space, which will be left between the

body of the alembic and the top of the upper part of the furnace, must

be carefully filled up with Windsor-loam moistened; for without that

precaution the heat will soon reach the very head, which ought to be

kept as cool as possible, in order to promote the condensation of the

vapours. On this occasion therefore it will be proper to leave no holes

open in the fire-place, but the lateral ones; of which also those

over-against the receiver must be stopped.

A pot, or broad-brimmed earthen pan, may be placed over this furnace,

and being so fitted to it as to close the upper part thereof

accurately, and filled with sand, may serve for a sand-heat to distil

with.

The bars designed to support distilling vessels being taken out, a

crucible may stand therein, and many operations be performed that do

not require the utmost violence of fire. In a word, this furnace is one

of the most commodious that can be, and more extensively useful than

any other.

The Melting furnace is designed for applying the greatest force of

heat to the most fixed bodies, such as metals and earths. It is never

employed in distilling: it is of no use but for calcination and fusion;

and consequently need not admit any vessels but crucibles.

The ash-hole of this furnace differs from that of the reverberating

furnace only in this, that it must be higher, in order to raise the

fire-place to a level with the artist's hand; because in that all

the operations of this furnace are performed. The ash-hole therefore

must be about three feet high: and this heighth procures it moreover

the advantage of a good draught of air. For the same reason, and in

consequence of the principles we laid down, it should be so built that

its width lessening insensibly from the bottom to the top, it may be

narrower where it opens into the fire-place than any where below.

The ash-hole is terminated at its upper end, like that of the

reverberating furnace, by a grate, which serves for the bottom of

the fire-place, and ought to be very substantial, that it may resist

the violence of the fire. The inside of this furnace is commonly an

elliptic curve; because it is demonstrated by mathematicians that

surfaces having that curvature reflect the rays of the sun, or of fire,

in such a manner, that meeting in a point, or a line, they produce

there a violent heat. But, to answer this purpose, those surfaces must

be finely polished; an advantage hardly procurable to the internal

surface of this furnace, which can be made of nothing but earth:

besides, if it were possible to give it a polish, the violent action of

the fire that must be employed in this furnace would presently destroy

it. Yet the elliptical figure must not be entirely disregarded: for,

if care be taken to keep the internal surface of the furnace as smooth

as possible, it will certainly reflect the heat pretty strongly, and

collect it about the center.

The fire-place of this furnace ought to have but four apertures.

First, that of the lower grate, which communicates with the ash-hole.

Secondly, a door in its fore-side, through which may be introduced

coals, crucibles, and tongs for managing them: this aperture should be

made to shut exactly with a plate of iron, having its inside coated

with earth, and turning on two hinges fixed to the furnace.

Thirdly, over this door a hole slanting downwards, towards the place

where the crucible is to stand. The use of this hole is to give the

operator an opportunity of examining the condition of the matters

contained in his crucible without opening the door of the fire-place:

this hole should be made to open and shut easily, by means of a stopple

of earth.

Fourthly, a circular aperture of about three inches wide in the upper

part or vault of the furnace, which should gradually lessen and

terminate, like that of the dome of the reverberating furnace, in a

short conical funnel of about three inches long, and fitted to enter

the conical pipe before described, which is applied when the activity

of the fire is to be increased.

When this furnace is to be used, and a crucible to be placed in it,

care must be taken to set on the grate a cake of baked earth, somewhat

broader than the foot of the crucible. The use of this stand is to

support the crucible, and raise it above the grate, for which purpose

it should be two inches thick. Were it not for this precaution the

bottom of the crucible, which would stand immediately on the grate,

could never be thoroughly heated, because it would be always exposed to

the stream of cold air which enters by the ash-hole. Care should also

be taken to heat this earthen bottom red-hot before it be placed in the

furnace, in order to free it from any humidity, which might otherwise

happen to be driven against the crucible during the operation, and

occasion its breaking.

We omitted to take notice, in speaking of the ash-hole, that, besides

its door, it should have about the middle of its heighth a small hole,

capable of receiving the nosel of a good perpetual bellows, which is

to be introduced into it and worked, after the door is exactly shut,

when it is thought proper to excite the activity of the fire to the

utmost violence. The Forge is only a mass of bricks of about three

feet high, along whose upper surface is directed the nose or pipe of a

pair of large perpetual bellows, so placed that the operator may easily

blow the fire with one hand. The coals are laid on the hearth of the

forge near the nose of the bellows; they are confined, if necessary,

to prevent their being carried away by the wind of the bellows, within

a space inclosed by bricks; and then by pulling the bellows the fire

is continually kept up in its greatest activity. The forge is of use

when there is occasion to apply a great degree of heat suddenly to any

substance, or when it is necessary that the operator be at liberty to

handle frequently the matters which he proposes to fuse or calcine.

The Cupelling furnace is that in which gold and silver are purified, by

the means of lead, from all alloy of other metallic substances. This

furnace must give a heat strong enough to vitrify lead, and therewith

all the alloy which the perfect metals may contain. This furnace is to

be built in the following manner.

First, of thick iron plates, or of some such composition of earth as we

recommended for the construction of furnaces, must be formed a hollow

quadrangular prism, whose sides may be about a foot broad, and from ten

to eleven inches high; and extending from thence upwards may converge

towards the top, so as to form a pyramid truncated at the heighth of

seven or eight inches, and terminated by an aperture of the width

of seven or eight inches every way. The lower part of the prism is

terminated, and closed, by a plate of the same materials of which the

furnace is constructed.

Secondly, in the fore-side or front of this prism there is an opening

of three or four inches in heighth, by five or six inches in breadth:

this opening, which should be very near the bottom, is the door of the

ash-hole. Immediately over this opening is placed an iron grate, the

bars of which are quadrangular prisms of half an inch square, laid

parallel to each other, and about eight or nine inches asunder, and

so disposed that two of their angles are laterally opposite, the two

others looking one directly upwards and the other downwards. As in this

situation the bars of the grate present to the fire-place very oblique

surfaces, the ashes and very small coals do not accumulate between

them, or hinder the free entrance of the air from the ash-hole. This

grate terminates the ash-hole at its upper part, and serves for the

bottom of the fire-place.

Thirdly, three inches, or three and a half, above the grate, there is

in the fore-side of the furnace another opening, terminated by an arch

for its upper part, which consequently has the figure of a semi-circle:

it ought to be four inches wide at bottom, and three inches and an half

high at its middle. This opening is the door of the fire-place; yet

it is not intended for the same uses as the door of the fire-place in

other furnaces: the purpose for which it is actually destined shall

be explained when we come to shew how the furnace is to be used. An

inch above the door of the fire-place, still in the fore-side of the

furnace, are two holes of about an inch diameter, and at the distance

of three inches and a half from each other, to which answer two other

holes of the same size, made in the hinder part, directly opposite to

these. There is, moreover, a fifth hole of the same width about an inch

above the door of the fire-place. The design of all these holes shall

be explained when we describe the manner in which these furnaces are to

be used.

Fourthly, the fore-part of the furnace is bound by three iron braces,

one of which is fixed just below the door of the ash-hole; the second

occupies the whole space between the ash-hole door and the door of

the fire-place, and has two holes in it, answering to those which we

directed to be made in the furnace itself about this place; and the

third is placed immediately over the door of the fire-place. These

braces must extend from one corner of the front of the furnace to the

other, and be fastened thereto with iron pins, in such a manner that

their sides next to the doors may not lie quite close to the body of

the furnace, but form a kind of grooves for the iron plates to slide

in, that are designed to shut the two doors of the furnace when it is

necessary. Each of these iron plates should have a handle, by which it

may be conveniently moved; and to each door there should be two plates,

which meeting each other, and joining exactly in the middle of the

door-place, may shut it very close. Each of the two plates belonging

to the door of the fire-place ought to have a hole in its upper part;

one of these holes should be a slit of about two lines wide, and half

an inch long; the other may be a semi-circular opening of one inch

in heighth and two in breadth. These holes should be placed so that

neither of them may open into the fire-place when the two plates are

joined together in the middle of the door to shut it close.

Fifthly, to terminate the furnace above, there must be a pyramid formed

of the same materials with the furnace, hollow, quadrangular, three

inches high on a base of seven inches, which base must exactly fit

the upper opening of the furnace: the top of this pyramidal cover must

end in a tube of three inches in diameter and two in heighth, which

must be almost cylindrical, and yet a little inclining to the conical

form. This tube serves, as in the furnaces already described, to carry

the conical funnel, which is fitted to the upper part when a fire of

extraordinary activity is wanted.

The furnace thus constructed is fit to serve all the purposes for

which it is designed: yet before it can be used another piece must be

provided, which, though it does not properly belong to the furnace, is

nevertheless necessary in all the operations performed by it; and that

is a piece contrived to contain the cupels, or other vessels which are

to be exposed to the fire in this furnace. It is called a Muffle, and

is made in the following manner.

On an oblong square, of four inches in breadth, and six or seven in

length, a concave semi-cylinder is erected, in the form of a vault,

which makes a semi-circular canal, open at both ends. One of these

is almost entirely closed, except that near the bottom two small

semi-circular holes are left. In each of its sides likewise two such

holes are made, and the other end is left quite open.

The Muffle is intended to bear and communicate the fiercest heat; and

therefore it must be made thin, and of an earth that will resist the

violence of fire, such as that of which crucibles are made. The Muffle

being thus constructed, and then well baked, is fit for use.

When it is to be used it must be put into the furnace by the upper

opening, and set upon two iron bars, introduced through the holes

made for that purpose below the door of the fire-place. The Muffle

must be placed on these bars in the fire-place in such a manner that

its open end shall stand next to, and directly against the door of

the fire-place, and may be joined to it with lute. Then the cupels

are ranged in it, and the furnace is filled up, to the heighth of two

or three inches above the Muffle, with small coals not bigger than

a walnut, to the end that they may lie close round the Muffle, and

procure it an equal heat on every side. The chief use of the Muffle

is to prevent the coals and ashes from falling into the cupels, which

would be very prejudicial to the operations carrying on in them:

for the lead would not vitrify as it ought, because the immediate

contact of the coals would continually restore its phlogiston; or

else the glass of lead, which ought to penetrate and pass through the

cupels, would be rendered incapable of so doing; because the ashes

mixing therewith would give it such a consistence and tenacity as

would destroy that property, or at least considerably lessen it. The

openings, therefore, which are left in the lower part of the Muffle,

should not be so high as to admit coals or ashes to get into the

cupels; the use of them is to procure an easier passage for the heat

and the air to those vessels. The Muffle is left quite open in its

fore-part, that the operator may be at liberty to examine what passes

in the cupels, to stir their contents, to remove them from one place

to another, to convey new matters into them, &c. and also to promote

the free access of the air, which must concur with the fire towards the

evaporation necessary to the vitrification of lead; which air, if fresh

were not often enough admitted, would be incapable of producing that

effect; because it would soon be loaded with such a quantity of vapours

that it could not take up any more.

The government of the fire in this furnace is founded on the general

principles above laid down for all furnaces. Yet as there are some

little differences, and as it is very essential to the success of the

operations for which this furnace is intended, that the artist should

be absolutely master of his degree of heat, we shall in few words shew

how that may be raised or lowered.

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._

Chymical vessels, especially such as are made of glass, and the earthen

vessels commonly called stone-ware, are very subject to break when

exposed to sudden heat or cold: whence it comes, that they often crack

when they begin to heat, and also when being very hot they happen to be

cooled, either by fresh coals thrown into the furnace, or by the access

of cold air. There is no way to prevent the former of these accidents,

but by taking the pains to warm your vessel very slowly, and by almost

insensible degrees. The second may be avoided by coating the body of

the vessel with a paste or lute, which being dried will defend it

against the attacks of cold.

The fittest stuff for coating vessels is a composition of fat earth,

Windsor-loam, fine sand, filings of iron, or powdered glass, and

chopped cow's hair, mixed and made into a paste with water. This lute

serves also to defend glass vessels against the violence of the fire,

and to prevent their melting easily.

In almost all distillations it is of great consequence, as hath been

said, that the neck of the distilling vessel be exactly joined with

that of the receiver into which it is introduced, in order to prevent

the vapours from escaping into the air and so being lost: and this

junction is effected by means of a lute.

A few slips of paper applied round the neck of the vessels with common

size will be sufficient to keep in such vapours as are aqueous or not

very spirituous.

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.

[Illustration: Decorative Scroll]

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.