"The second vessel, into which the liquor is first decanted, he also

lays declining, that a new precipitation of the undissolved matters may

be obtained; after which he pours the liquor into a third vessel. This

liquor must not be filtered, if you would have the rest of the process

succeed perfectly; because the _aqua fortis_ would dissolve some of the

paper, and that would spoil the colour of your paper.

"When this solution, which Mr. Hellot calls the _Impregnation_, is

thoroughly clarified by being decanted three or four times, he puts

it into a glass bason with two ounces of very pure Sea-salt. The fine

white salt made by the sun succeeded best with Mr. Hellot. If that

cannot be had, common bay-salt, purified by solution, filtration,

and crystallization, may be used instead of it. But as it is rare to

meet with any of the sort that is not a little tainted with iron,

the white bay-salt is to be preferred. The glass bason he sets in a

gentle sand-heat, and keeps it there till the mixture be reduced by

evaporation to an almost dry saline mass.

"If you desire to save the _aqua regis_, the impregnation must be put

into a retort, and distilled with the gentle heat of a sand-bath. But

there is an inconveniency, as Mr. Hellot observes, in employing a

retort; which is, that, as the saline mass cannot be stirred while it

coagulates in the retort, it is reduced to a compact cake of coloured

Salt, which presents but one single surface to the water in which it

must be dissolved; so that the dissolution thereof takes up sometimes

no less than five or six days. In the bason, on the contrary, the

saline mass is easily brought to a granulated Salt, by stirring it

with a glass rod; and, when thus granulated, it has a great deal more

surface; it dissolves more easily, and yields its tincture to water

in four hours time. Indeed one is more exposed to the vapours of the

solvent, which would be dangerous, if the operation were to be often

performed, without proper precautions.

"When the bason, or little vessel, containing the mixture of the

Impregnation and Sea-salt is heated, the liquor, which was of an

orange-coloured red, becomes a crimson red; and, when all the phlegm of

the solvent is evaporated, it acquires a beautiful emerald colour. By

degrees it thickens, and acquires the colour of a mass of Verdegris.

It must then be carefully stirred with the glass rod, in order to

granulate the Salt, which must not be kept over the fire till it be

perfectly dry; because you run a risk of losing irrecoverably the

colour you are seeking. You may be sure you have lost it, if by too

much heat the Salt that was of a green colour become of a dirty yellow.

If it be once brought to this state, it will continue without changing

when cold: but if care be taken to remove it from the fire while it

is still green, you will see it gradually grow pale, and become of a

beautiful rose colour as it cools.

"Mr. Hellot removes it from this vessel, and throws it into another

containing distilled rain water: and this second vessel he keeps in

gentle digestion till he observes that the powder which falls to the

bottom is perfectly white. If, after three or four hours digesting,

this powder still continues tinged with a rose colour, it is a proof

that water enough was not added to dissolve all the Salt impregnated

with the tincture of the solution. In this case, the first tinged

liquor must be poured off, and fresh water added, in proportion to the

quantity of tinged Salt, that is supposed to remain mixed with the

precipitate.

"When the ore is pure, and doth not contain a great deal of fusible

stone, commonly called _Fluor_ or _Quartz_, an ounce of it generally

yields tincture enough for eight or nine ounces of water, and the

liquor is of a beautiful colour like that of the lilach or pipe-tree

blossom. In order to prove the effect of this tincture, you must write

with this lilach-coloured liquor on good well-gummed paper, that does

not sink: or you may use it to shade the leaves of some tree or plant,

having first drawn the outlines thereof lightly, with China-ink or

with a black-lead pencil. Let this coloured drawing, or writing, dry

in a warm air. You will perceive no colour while it is cold; but if

it be gently warmed before the fire, you will see the writing, or the

drawing, gradually acquire a blue or greenish-blue colour, which is

visible as long as the paper continues a little warm, and disappears

entirely when it cools."

The singularity of this sympathetic ink consists in its property of

disappearing entirely and becoming invisible, though it be not touched

with any thing whatever: and this distinguishes it from all others;

which, when once rendered visible by the application of proper means,

do not again disappear, or at least not without touching the strokes on

the paper with some other liquor.

Mr. Hellot made a vast variety of experiments on this subject, and gave

his sympathetic ink successively the properties of all others that are

known.

It follows from Mr. Hellot's experiments, that it is the Acid of

Sea-salt which makes this saline _magma_ of a green colour while it

is hot: that without this Acid the saline matter continues red; and

that the solution of Bismuth-ore in _aqua fortis_ may therefore serve

as a touchstone, to discover whether or no any unknown Salt under

examination contains Sea-salt, or a portion of the Marine Acid.

He also proves, in the Memoirs he hath given in on this subject,

that the Nitrous Acid is the true solvent of those ores of Bismuth

which contain moreover Smalt and Arsenic. That Acid dissolves all the

metallic and colouring matters contained in those ores, sparing nothing

but the sulphureous and arsenical portion, the greatest part of which

remains precipitated; and from this colouring matter the sympathetic

ink derives its virtue.

Under the head of Arsenic we shall speak more amply of this matter in

Cobalt, or the ore of Arsenic, that gives a blue colour to the sand

with which it is vitrified.

The Vitriolic Acid does not, properly speaking, dissolve Bismuth. If

to one part and an half of this semi-metal you add one part of Oil of

Vitriol; distil the whole to dryness; and then lixiviate with water

what remains in the retort; the liquor you obtained by this means will

be of a reddish yellow colour, but will let nothing fall when mixed

with an Alkali: and this shews that the Vitriolic Acid acts only upon

the inflammable part of Bismuth, and doth not dissolve its metallic

earth.

It dissolves the ore of Bismuth more perceptibly than Bismuth itself;

because the ore contains, besides the reguline part, an arsenical

matter, and a coloured matter, over which perhaps it hath more power.

The Acid of Sea-salt attacks and dissolves Bismuth in some small

measure, but slowly and with difficulty. That this Acid dissolves a

portion of our semi-metal may be proved, by mixing a Fixed or Volatile

Alkali with Spirit of Salt in which Bismuth hath lain some time

digesting; for then a precipitate falls.

But, though the Marine Acid be capable of dissolving Bismuth, it doth

not follow that it hath a greater affinity than the Nitrous Acid with

this metallic substance, as some Chymists have thought; who imagined

that, in the precipitation of the Magistery of Bismuth by a solution

of Sea-salt, the Acid of that Salt quits its basis to unite with the

Bismuth which it precipitates, as is the case in the precipitations

of Lead and of Silver by the same Salt, and that it forms, on this

occasion, a _Bismuthum corneum_.

On this subject, Mr. Pott observed, 1. that, when only a small quantity

of the solution of Sea-salt is mixed with the solution of Bismuth in

the Nitrous Acid, no precipitate is formed: now it is certain that when

the smallest quantity whatever of Sea-salt is mixed with the solution

either of Lead or of Silver, a precipitate is immediately deposited, in

a quantity proportioned to that of the Salt used.

2. Mr. Pott, having examined the precipitate of Bismuth thrown down

by a solution of Sea-salt, found it not to have the properties of a

metallic substance rendered horny: on the contrary, that precipitate

being exposed to a very violent fire appeared refractory, and could not

be melted.

CHAP. III.

_Of_ ZINC.

PROCESS I.

_To extract Zinc from its Ore, or Calamine._

Take eight parts of Calamine reduced to a powder; mix this powder

accurately with one part of fine charcoal-dust, previously calcined

in a crucible to free it from all moisture: put this mixture into a

stone retort coated with lute, leaving a third part of it empty: set

your retort in a reverberatory furnace, capable of giving a very fierce

heat. To the retort apply a receiver, with a little water in it. Kindle

the fire, and raise it by degrees till the heat be strong enough to

melt Copper. With this degree of fire the Zinc being metallized will

separate from the mixture, and sublime into the neck of the retort,

in the form of metallic drops. Break the retort when it is cold, and

collect the Zinc.

_OBSERVATIONS._

The process here given for smelting Zinc out of Calamine is taken from

the Memoirs of the Academy of Sciences at Berlin. The author of it is

Mr. Marggraff, a skilful Chymist, whom we have already had occasion to

mention under the article of Phosphorus.

Till this process was published, we knew no method of obtaining pure

Zinc directly from the _Lapis Calaminaris_.

Most of the Zinc we have comes from an ore of difficult fusion that is

worked at Goslar, and yields, at one and the same time, Lead, Zinc, and

another metallic matter called _Cadmia Fornacum_, which also contains

much Zinc, as we shall afterwards see.

The furnace used for smelting this ore is closed on its fore-side with

thin plates or tables of stone, not above an inch thick. This stone is

greyish, and bears a violent fire.

In this furnace the ore is melted amidst charcoal, by the help of

bellows. Each melting takes twelve hours, during which time the Zinc

flowing with the Lead is resolved into flowers and vapours, great part

of which adheres to the sides of the furnace in the form of a very hard

crust of earth. The workmen take care to remove this crust from time

to time; for it would otherwise grow so thick at last as to lessen the

cavity of the furnace very considerably.

There adheres moreover to the fore-part of the furnace, which is

formed, as we said before, of thin plates of stone, a metallic matter,

which is the Zinc, and is carefully collected at the end of each

melting, by removing from this part all the live coals. A quantity

of small coal is laid unlighted at the bottom; and on this small

coal, by striking the stone plates gently with a hammer, the Zinc

is made to fall out of the other matter, known by the Latin name

of _Cadmia Fornacum_, among which it appears fixed in a radiated

form. To this other matter we may properly enough give the name of

_Furnace-Calamine_. The Zinc falls in the form of a melted metal, all

on fire, and in a bright flame. It would soon be entirely burnt and

reduced to flowers, as we shall see, if it were not extinguished, and

easily cooled and fixed, by being hid under the unlighted small-coal

placed below on purpose to receive it.

The Zinc adheres to the fore-part of the furnace preferably to any

other, because that being the thinnest is therefore the coolest: and,

in order further to promote its fixing on this part, they take care to

keep the thin stone plates cool during the operation, by throwing water

on them.

Hence it appears, that Zinc is not extracted from its ore by fusion and

the precipitation of a Regulus, like other metallic substances. This is

owing to the great volatility of our semi-metal, which cannot, without

subliming, bear the degree of fire necessary to melt its ore. It is at

the same time so combustible, that a great part of it rises in flowers

which have not the metalline form.

Mr. Marggraff provides against these inconveniences by working the

ore of Zinc in close vessels. By this means he prevents the Zinc from

taking fire, and being converted into flowers; so that it sublimes in

its metalline form. The water in the recipient serves to receive and

cool the drops of Zinc that may be forced quite over the helm. As the

operation requires a most violent fire, these drops must needs issue

exceeding hot, and, without this precaution, break the recipient.

Mr. Marggraff by the same process extracted Zinc out of the

Furnace-Calamine procured from ores containing Zinc; from Tutty, which

is a sort of furnace-calamine; from the flowers and from the calx of

Zinc; and from the precipitate of White Vitriol; all of them matters

known to be Zinc, that wanted nothing but the phlogiston to give it a

semi-metalline form, and from which nevertheless no body could ever

before him procure any Zinc.

Mr. Marggraff observes, that the Zinc obtained by his process bears

being flatted under the hammer into pretty thin plates; which the

common Zinc will not do. The cause of this probably is, that the Zinc

obtained by his method is more intimately combined with the phlogiston,

and contains a greater quantity thereof, than that which is procured in

the ordinary way.

PROCESS II.

_To sublime Zinc into Flowers._

Take a very deep, large crucible: place it in a furnace, so that it may

stand inclining in an angle of forty-five degrees nearly. Throw some

Zinc into it, and kindle a fire in the furnace somewhat stronger than

would be necessary to keep Lead in fusion. The Zinc will melt. Stir it

with an iron wire, and there will appear on its surface a very bright

white flame: two inches above this flame a thick smoke will be formed,

and with this smoke exceeding white Flowers will rise, and remain some

time adhering to the sides of the crucible, in the form of a very fine

light down. When the flame slackens, stir your melted matter again with

the iron wire: you will see the flame renewed, and the flowers begin

again to appear in greater abundance. Go on thus till you observe that

the matter will not flame, nor any more Flowers rise.

_OBSERVATIONS._

Zinc takes fire very easily as soon as it is affected by a certain

degree of heat; which proves, that in the composition of this

semi-metal there is very much phlogiston, united but slightly with

its metallic earth. The Flowers into which Zinc resolves, during its

combustion, are of a perfectly singular nature, and differ greatly from

all the other productions obtainable out of metallic substances.

They may be considered as the very calx of Zinc, or its metallic earth

robbed of its phlogiston, and sublimed during the combustion of this

semi-metal, being probably carried up by the phlogiston in flying off.

For these Flowers, when once sublimed, are afterwards exceedingly

fixed: they sustain the greatest violence of fire without rising, and

are converted by it into a sort of glass.

None of the methods hitherto employed, for restoring to the Flowers

of Zinc their metalline form, have ever succeeded. When treated like

other metalline calces in a crucible, with every kind of inflammable

matter, and different sorts of reducing fluxes, they never can be

re-metallized: they only melt with the flux, and produce a kind of

Glass.

Mr. Marggraff indeed, as mentioned before, obtained Zinc from these

Flowers, by treating them as he did Calamine in a retort with

charcoal-dust: but as the Flowers often carry up with them little

particles of undecomposed Zinc, there still remains some doubt

concerning the reduction of these Flowers, even by this method.

If the crucible, into which you put the Zinc to be converted into

Flowers, instead of being left open, as directed, be covered with

another crucible inverted, the two vessels luted together, placed in

a melting furnace, and a strong fire immediately kindled and kept up

for about half an hour; you will find, when the vessels are cold, that

all the Zinc hath left the lower crucible, and is sublimed into the

upper one, in its metalline form, without suffering any decomposition.

This experiment proves, that Zinc, to be converted into Flowers, must

necessarily be set on fire and burnt. As it cannot burn in close

vessels, any more than other combustible bodies, and as it is volatile,

it sublimes without suffering any decomposition. Regulus of Antimony

and Bismuth may be sublimed in the same manner; but not so easily as

Zinc, which is still more volatile than those other semi-metals.

It is necessary to stir the Zinc in fusion from time to time with

an iron wire, when you intend to convert it into Flowers: for there

forms on its surface a grey crust that obstructs its deflagration,

and beneath which it is gradually converted into a clotted calx. In

order, therefore, to promote the rising of the flowers, care must be

taken to break this crust, as oft as it begins to form. On this there

immediately appears a very bright white flame: two inches above the

flame is seen a thick smoke, and with this smoke very white Flowers

rise, that continue some time adhering to the inside of the crucible,

in the form of a fine down.

M. Malouin, who, in sundry Memoirs on Zinc, hath endeavoured to

discover what resemblance there is between this semi-metal and Tin,

tried to calcine Zinc in the same manner as Tin; but found it somewhat

more difficult. Zinc, while it is not in fusion, doth not calcine; but

it begins to turn to a calx the moment it begins to melt. M. Malouin,

having repeated the fusion of Zinc a great number of times, by that

means collected at last a quantity of the calx of this semi-metal,

resembling other metalline calces. This calx of Zinc he melted in

a crucible with animal fat; whereby the calx was re-metallized, and

reduced to Zinc. There is great reason to believe that the calx of Zinc

made by this method is not so much burnt as the Flowers, and that it

still contains a portion of phlogiston.

PROCESS III.

_To combine Zinc with Copper. Brass. Prince's Metal_, &c.

Pound one part and an half of Calamine, and an equal quantity of

charcoal: mingle these two powders together, and moisten them with a

little water. Put this mixture into a large crucible, or some other

earthen vessel that will bear a melting heat. Amongst and over this

mixture put one part of very pure Copper in thin plates, and then put

fresh charcoal-dust over all: cover the crucible; set it in a melting

furnace; put coals all round it, and let them kindle gradually. Raise

the fire so as to make the crucible very red-hot. When you observe

that the flame hath acquired a purple or bluish-green colour, uncover

the crucible, and dip into it an iron wire, to examine whether or no

the copper be in fusion under the charcoal-dust. If you find it is,

moderate the force of the fire a little, and let your crucible remain

in the furnace for a few minutes. Then take it out and let it cool: you

will find your Copper of a gold colour, increased in weight a fourth,

or perhaps a third part, and yet very malleable.

_OBSERVATIONS._

The _Lapis Calaminaris_ is not the only substance with which Copper

may be converted into brass: all other ores containing Zinc, the

Furnace-Calamine that sublimes where such ores are worked, Tutty, Zinc

in substance, may be substituted for it, and, like it, will make very

fine Brass; but, in order to succeed, sundry precautions are necessary

which we shall now lay before you.

This process is a sort of cementation: for the Calamine doth not melt;

only the Zinc is converted into vapours, and then combines with the

Copper. On this the success of the operation partly depends, as it

is the means of the Copper's preserving its purity and malleability;

because the other metallic substances that may be united with the ore

of Zinc, or with the Zinc itself, not having the same volatility,

cannot be reduced to vapours. If you are apprised that the Calamine,

or other ore of Zinc used on this occasion, is contaminated with a

mixture of any other metallic matter, you must mingle luting earth

with the charcoal-dust and the matter containing the Zinc; make it

into stiff paste with water; of this make a bed at the bottom of your

crucible, and ram it hard down; lay the Copper plates thereon, cover

them with charcoal-dust, and then proceed as before. By this means when

the Copper melts it cannot fall to the bottom of the crucible, nor mix

with the ore; but is borne up by the mixture, and cannot combine with

any thing but the Zinc, that rises in vapours, and, passing through the

lute, fixes in the Copper.

_Lapis Calaminaris_, or other ore of Zinc, may also be purified before

it be used for making Brass; especially if adulterated with Lead ore,

which is often the case. For this purpose the ore must be roasted in

a fire strong enough to give a small degree of fusion to the leaden

matter; which will thereby be reduced into larger, heavier, and tougher

masses. The most subtile particles are dissipated in the torrefaction,

together with some of the Calamine. The Calamine, on the contrary, is

by roasting made more tender, lighter, and much more friable. When it

is in this condition, put it into a washing tray or van; dip the tray

in a vessel full of water, and bruise the matter it contains. The water

will carry off the lightest powder, which is the Calamine, and leave

nothing at the bottom of the tray but the heaviest substance; that is

the leaden matter, which is to be rejected as useless. The powder of

the Calamine will settle at the bottom of the vessel, where, after

pouring off the water, it may be found, and used as above directed.

In this operation the charcoal-dust serves to prevent both the Copper

and the Zinc from being calcined: and for this reason, when you work

on a great quantity of materials at once, it is not necessary to use

so much charcoal-dust, in proportion, as when you work but on a small

quantity; because, the greater the mass of metal, the less easily will

it calcine.

Though the Copper melts in this operation, yet it is far from being

necessary to apply such a strong fire as Copper usually requires to

melt it: for the accession of the Zinc, on this occasion, communicates

to it a great deal of fusibility. The increase of its weight is also

owing to the quantity of Zinc combined with it. Copper acquires still

another advantage by its association with this semi-metal; for it

remains longer in the fire without calcining.

Brass well prepared ought to be malleable when cold. But in whatever

manner it be made, and whatever proportion of Zinc there be in it, it

is constantly found quite unmalleable when red-hot.

Brass melted in a crucible, with a fierce heat, takes fire almost like

Zinc, and from its surface many white flowers ascend, dancing about

in flakes like the flowers of Zinc. They are indeed the flowers of

Zinc, and the flame of Brass urged by a strong fire is no other than

the flame of the Zinc that is united with the Copper, and at that

time burns. If Brass be thus kept long in fusion it will lose almost

all the Zinc it contains. It will also lose much of its weight, and

its colour will be nearly that of Copper. It is therefore necessary,

towards performing this operation aright, to seize the moment when the

Copper is sufficiently impregnated with Zinc, when it hath acquired

the most weight and the finest colour, with the least detriment to its

ductility, that is possible, and that instant to put out the fire;

because, if the Copper be left longer in fusion, it will only lose

the Zinc already united with it. Skill acquired by much practice, and

an acquaintance with the particular Calamine employed, are necessary

to guide the artist surely through this operation; for there are very

considerable differences between the sundry ores of Zinc. Some of them

contain Lead, as was said above, and in others there is Iron. When

these heterogeneous metals come to be mixed with the Copper, they do

indeed augment its weight, but they render it at the same time pale,

and make it very harsh. Some Calamines require to be roasted before

they can be used for this purpose, and in the torrefaction emit vapours

of a Volatile Alkali, succeeded by vapours of a Sulphureous Spirit:

others exhale no vapours while roasting, and may be employed without

any antecedent preparation. These different qualities must evidently

produce great differences in the operation.

Brass may also be made as Prince's metal and other imitations of Gold

are actually made, by using Zinc in substance, instead of the ores that

contain it. But these compositions have not, when cold, the ductility

of Brass prepared with _Lapis Calaminaris_, because Zinc is seldom

pure, or free from a mixture of Lead. Perhaps also the different

manner in which the Zinc unites with the Copper may contribute to this

variation.

To obviate this inconvenience, the Zinc must be refined from all alloy

of Lead. The property of being indissoluble by Sulphur, which this

semi-metal possesses, points out a very practicable method of doing

it. The Zinc must be melted in a crucible, and stirred briskly with

a strong iron wire, while tallow and mineral Sulphur are alternately

projected upon it; but so that the quantity of Sulphur may greatly

exceed that of the tallow. If the Sulphur do not burn entirely away,

but form a kind of scoria on the surface of the Zinc, it is a sign

that your semi-metal contains Lead. In this case you must continue

throwing in more Sulphur, and keep stirring the Zinc incessantly, till

you perceive that the Sulphur ceases to unite any more with a metallic

substance, but burns freely on the surface of the Zinc. The semi-metal

is then refined, because the Sulphur, which cannot dissolve it, unites

very readily with the Lead, or other metallic substance, contained in

it.

If Zinc thus refined be mixed with pure Copper, in the proportion

of a fourth or a third part, and the mixture be kept in fusion and

constantly stirring for some time, the Brass produced will be as

ductile, when cold, as that made by cementation with the _Lapis

Calaminaris_.

With regard to Prince's metal, and other imitations of Gold, they are

made either with Copper or Brass re-combined with more Zinc. As it is

necessary, for giving them a fine golden colour, to mix with them other

proportions of Zinc than that acquired to make Brass only, they are

generally much less ductile. In 1725, M. Geoffroy gave a Memoir on this

subject in which he examined the effects of incorporating both Copper

and Brass with Zinc, from a small to a very large quantity.

PROCESS IV.

_Zinc dissolved in the Mineral Acids_.

Weaken concentrated Oil of Vitriol by mixing with it an equal quantity

of water. Into a matrass put the Zinc you intend to dissolve, first

broken to small pieces. Pour on it six times its weight of the

Vitriolic Acid, lowered as above directed, and set the matrass in a

sand-bath gently heated. The Zinc will dissolve entirely, without any

sediment. The Neutral Metallic Salt resulting from this dissolution

shoots into crystals, which go by the name of _White Vitriol_, or

_Vitriol of Zinc_.

_OBSERVATIONS_.

Though Zinc be soluble in all the Acids, and when combined with

those Acids exhibits some uncommon phenomena, yet M. Hellot is the

first that ever gave a particular account of what happens in those

dissolutions: so that all we have to say on this head is extracted

from that Gentleman's Memoirs. If a solution of Zinc in the Vitriolic

Acid, prepared according to the directions in the process, be

distilled from a retort placed in a sand-bath with a graduated heat,

almost half the liquor presently comes over in pure phlegm. A small

quantity of a Sulphureous Acid Spirit rises next. A greater force of

fire is now requisite: the retort must therefore be removed into a

reverberatory, and the distillation continued with a naked fire. On the

first impression of this heat an odour of Liver of Sulphur discovers

itself, which becomes sharp and suffocating towards the end of the

distillation. In two hours time white vapours begin to appear, as in

the rectification of common Oil of Vitriol. If the receiver be then

shifted, you will obtain an Oil of Vitriol, in quantity about the

eighteenth part of the whole used in the distillation, which, though

sulphureous, is yet so concentrated, that, if a few drops thereof be

poured into a weak Oil of Vitriol, they fall to the bottom with as much

noise as if they were so many bits of red-hot iron, and heat this Oil

of Vitriol as much as common Oil of Vitriol heats water.

At the bottom of the retort there remains a dry, white, crystalline,

saline mass, exceeding in weight the Zinc that was dissolved, about

a twelfth part of the whole weight of the liquor. The increase of

its weight is owing to a portion of the Vitriolic Acid that remains

concentrated in the Zinc, and could not be expelled by the fire. This

portion of Acid adheres to it most tenaciously: for, though M. Hellot

kept the retort containing it during two whole hours in so violent a

fire that the vessel began to melt, the smallest vapour did not rise

from it.

This saline _caput mortuum_ is in the form of needles, much like

the Sedative Salt. It is caustic, grows considerably hot when water

is poured on it, and gives in the air, but slowly. Spirit of wine,

digested with this Salt for eight or ten days, acquires the same smell

as that which is mixed with concentrated Oil of Vitriol in preparing

Æther.

Zinc is dissolved by the Nitrous and Marine Acids, much in the same

manner as by the Vitriolic; except that the Marine Acid does not touch

a black, spungy, rarefied matter, which it separates from the Zinc. M.

Hellot found upon trial that this matter is not Mercury, and that it

cannot be reduced to a metallic substance.

That ingenious Chymist distilled likewise Solutions of Zinc in the

Nitrous and Marine Acids. There came over at first, as there did from

the solution made by the Vitriolic Acid, an aqueous, and then an

acidulated liquor. At last, by exciting the fire with great violence,

towards the end of the distillation, he obtained a small quantity of

the Acid that hath been employed in the dissolution: but the small

portion of Acid thus obtained was exceeding strong; and the quantity of

the Nitrous much more considerable than that of the Marine Acid.

A solution of Zinc in the Marine Acid, being distilled to dryness,

yields a Sublimate on applying a violent heat to it.

All the Acids dissolve with ease, not only Zinc, but its Flowers

also; and that nearly in the same quantity, and with almost all the

same phenomena. M. Hellot, observing that the residues of most of the

solutions of Zinc have a great resemblance with its flowers, is of

opinion that this semi-metal may be reduced, by the means of solvents,

to the same state into which it is brought by the fire when sublimed in

Flowers.

CHAP. IV.

_Of_ ARSENIC.

PROCESS I.

_To extract Arsenic from its Matrices. Zaffre or Smalt._

Powder some Cobalt, white Pyrites, or other Arsenical matters. Put

this powder into a retort with a short wide neck, leaving a full third

thereof empty. Set your retort in a reverberating furnace; lute on a

receiver; heat your vessel by degrees, and increase the fire till you

see a powder sublime into the neck of the retort. Keep up the fire in

this degree as long as the sublimation continues: when this begins

to slacken, raise your fire, and make it as strong as the vessels

will bear. When nothing more ascends, let it go out. On unluting the

vessels, you will find in the receiver a little Arsenic in the form of

a fine light _farina_. The neck of the retort will be full of white

flowers, not quite so fine, some of which will appear like little

crystals; and if a good deal of Arsenic be sublimed, a ponderous

matter, like a white, semi-transparent glass, will be found adhering to

that part of the neck of the retort which is next its body.

_OBSERVATIONS._

Arsenic is a metallic substance still more volatile than Zinc; so

that it cannot be separated from the matters with which it is mixed

otherwise than by sublimation. It is proper, however, to take notice,

that it is not naturally in a metallic form, and that, properly

speaking, the whole Sublimate obtained from Cobalt, as above directed,

is nothing but a metallic calx, that cannot be brought to the form and

gloss of a metal, till it be worked up with fatty matters, as we shall

shew in its place.

This calx is of a very singular nature, and differs from every other

metallic calx, in that this is volatile, and all the rest extremely

fixed; even those procured from the semi-metals: for the Flowers of

Zinc, which are justly considered as a calcined Zinc, though obtained

by a sort of sublimation, are not for all that of a volatile nature,

but rather exceedingly fixed; seeing they are capable of sustaining

the most violent fire, and melt instead of subliming. Arsenic, on the

contrary, is not only extracted from its ore by sublimation, but when

once sublimed continues to be volatile, and flies off in vapours as

soon as it is exposed even to a moderate degree of heat.

This metallic matter, before it is combined with the phlogiston, is

called _White Arsenic_, or plain _Arsenic_: it acquires the title

of _Regulus of Arsenic_ when it is united with the phlogiston, and

glitters like a metal.

Though Arsenic be volatile, yet it requires a pretty strong fire to

separate it from the minerals containing it, especially in close

vessels; because it adheres very close to earthy and vitrifiable

matters. This adhesion is so firm, that, when thus combined, it is

capable of bearing a melting heat, and vitrifies with metallic calces,

and other fusible matters. On this account it is impossible to extract

from Cobalt, or other Arsenical matters, all the Arsenic they contain

by working them only in close vessels. If such matters are to be

freed from all their Arsenic, you must, after you have extracted all

they will yield by distillation, put them into a crucible, and set

it uncovered in the midst of a strong fire. Many Arsenical vapours

will still rise; and care must be taken to stir the contents of the

crucible frequently with an iron rod, to facilitate the discharge of

the remaining Arsenic.

It often happens that the Arsenic, obtained from minerals by

sublimation, is not very white, but of a lighter or darker grey colour.

This is owing to some particles of inflammable matter, from which

Arsenical minerals are seldom quite free. A very small quantity of

phlogiston is sufficient to deprive much Arsenic of its whiteness,

and to give it a grey colour. But when fouled in this manner, it may

easily be brought to its due degree of whiteness: it need only be

sublimed once more, after mixing it with some substance on which it

doth not act; Sea-salt, for instance. If the matters from which Arsenic

is extracted contain Sulphur also, as some pyrites do, the Arsenic

sublimes with much less heat, than when it is united with earthy

matters only; because it combines with the Sulphur, wherewith it hath

a great affinity, and the Sulphur serves to separate the Arsenic, by

this interposition, from the earth. In consequence hereof, Sulphur may

be employed to extract Arsenic out of the earths in which it is fixed.

In this case, the Sulphur changes the colour of the Arsenic, which it

makes of a lighter or deeper yellow, or even red, in proportion to the

quantity there is of it, and to the degree of fire that hath acted on

both together.

The consistence of Arsenic is different, according to the degree of

heat applied in subliming it. If the Arsenical vapour meet with a cold

place, it gathers there in the form of a powder, as the Flowers of

Sulphur do: this is the case with that which falls into the receiver in

distilling it. But if it be stopped in a hot place, and cannot escape

from that heat, it condenses into a heavy, compact, semi-transparent

body, having undergone the first degree of fusion.

Yet it cannot be perfectly melted, so as to flow like other fused

matters: not that it is refractory; for, on the contrary, the degree of

heat in which it begins to melt is very moderate, and it is in its own

nature very fit to promote the fusion of refractory matters: but the

reason is this; it is necessarily converted into vapours by the degree

of heat necessary to fuse it, and these vapours burst the vessels, if

they find no vent.

Arsenic made yellow by a mixture of Sulphur, which is also called

_Orpiment_, is reducible to the form of a solid Sublimate with more

ease; because it is alloyed with a twentieth, or perhaps a tenth part,

of its weight of Sulphur, which renders it more fusible.

Red Arsenic, which contains still more Sulphur, melts also more easily.

It then becomes of a transparent red, like a ruby: and hence, when it

is in this form, it is called _Ruby of Arsenic_.

When a combination of Sulphur and Arsenic is wanted, it is better

to mingle and distil together such minerals as contain Sulphur and

Arsenic, the white and the yellow pyrites, for instance, than to mingle

pure Arsenic with pure Sulphur: for the great volatility of these two

substances is a hindrance to their uniting; whereas, when combined with

other matters, they are capable of sustaining a much greater degree of

heat, which favours and promotes their union.

Those who work by the grate do not extract Arsenic out of Cobalt by

distillation: they throw the ore mixed promiscuously with wood and

charcoal into a great furnace, from whence a flue carries the vapours

into a long winding passage, across which beams of wood are fixed at

proper distances from each other. The Arsenical vapours being conducted

into this passage, adhere both to the sides thereof and to the joists

that lye across it. The fuliginous parts of the combustible matters

being lighter ascend higher, and go out through a chimney at the

farther end of this passage.

The Arsenic sublimed by this method is not white, but of a grey colour;

owing to the inflammable matter of the wood and charcoal with which the

ore is torrefied.

When all the Arsenic the Cobalt will yield is thus separated, the

earthy fixed matter left behind is mixed with divers fusible matters

and vitrified, and produces a glass of a beautiful blue colour. It is

called _Smalt_. This glass is to be prepared in the following manner.

Take four parts of fine fusible sand, an equal quantity of any Fixed

Alkali perfectly depurated, and one part of Cobalt from which the

Arsenic hath been sublimed by torrefaction. Pulverize these different

substances very finely, and mix them thoroughly together; put the

mixture into a good crucible, cover it, and set it in a melting

furnace. Make a strong fire, and keep it up constantly in the same

degree for some hours. Then dip an iron wire into the crucible; to the

end of which a glassy matter will stick, in the form of threads, if the

fusion and vitrification be perfect. In this case take the crucible out

of the fire; cool it by throwing water on it, and then break it. You

will find in it a glass, which will be of an exceeding deep blue, and

almost black, if the operation hath succeeded. This glass, when reduced

to a fine powder, acquires a much brighter and more lively blue colour.

If you find after the operation that the glass hath too little colour,

the fusion must be repeated a second time, with twice or thrice the

quantity of Cobalt. If, on the contrary, the glass be too dark, less

Cobalt must be used.

Instead of the mixture here prescribed you may employ a ready-made

glass, providing it be white and fusible. But as glass is always

hard to melt, and as the mixing Cobalt with it renders it still more

refractory, therefore though an Alkaline Salt be one of the ingredients

in its composition, it is proper to promote the fusion, by mixing

therewith calcined wine-lees, in the quantity of one third part of the

weight of the Cobalt.

In order to make the assay of a particular Cobalt, with a view to know

what quantity of blue glass it will yield, it is necessary to perform

the operation in the manner here set down; a great deal of time and

trouble may be saved by melting one part of Cobalt with two or three

parts of Borax. This Salt is very fusible, and turns, when melted, into

a substance which, for a time, possesses all the properties of glass.

In this trial the glass of Borax will be nearly of the same colour as

the true glass, or Smalt, made with the same Cobalt.

The ores of Bismuth, as well as Cobalt, yield a matter that colours

glass blue; nay, the Smalt made with these ores is more beautiful than

that procured from the ore of pure Arsenic. Some Cobalts yield both

Arsenic and Bismuth. When such Cobalts are used, it is common to find

at the bottom of the crucible a little button of metallic matter, which

is called _Regulus of Cobalt_. This Regulus is a sort of Bismuth,

generally adulterated with a mixture of ferruginous and arsenical parts.

The heaviest and most fixed Flowers of Arsenic, procured from Cobalt,

have likewise the property of giving a blue colour to glass. But this

colour is faint: it is owing to a portion of the colouring matter

carried up along with the Arsenic. These Flowers may be made an

ingredient in the composition of blue glass, not only because of the

colouring principle they contain, but also because they greatly promote

fusion; Arsenic being one of the most efficacious fluxes known.

In short, all those blue glasses, or Smalts, contain a certain quantity

of Arsenic; for a portion of this semi-metal always remains united with

the fixed matter of the Cobalt, though roasted for a long time, and in

a very hot fire. The portion of Arsenic that is thus fixed vitrifies

with the colouring matter, and enters into the composition of the Smalt.

The blue glass made with the fixed part of Cobalt hath several names,

according to the condition in which it is. When it hath undergone the

first imperfect degree of fusion only it is called _Zaffre_. It takes

the name of _Smalt_ when perfectly vitrified: and this again being

pulverized is called _Powder-blue_, or, if finely levigated, _Blue

Enamel_; because it is used in enamelling, as well as in painting

earthen ware and porcelain.

PROCESS II.

_To separate Arsenic from Sulphur._

Powder the yellow or red Arsenic which you intend to separate from

its Sulphur. Moisten this powder with a Fixed Alkali resolved into a

liquor. Dry the mixture gently; put it into a very tall glass cucurbit,

and fit on a blind-head. Set this cucurbit in a sand-bath; warm the

vessels gently, and increase the fire by degrees, till you perceive

that no more Arsenic sublimes. The Arsenic, which before was yellow

or red, rises into the head partly in white flowers, and partly in a

compact, white, semi-transparent matter, which looks as if it were

vitrified. The Sulphur combined with the Fixed Alkali remains at the

bottom of the cucurbit.

_OBSERVATIONS._

A Fixed Alkali hath more affinity than any metallic substance with

Sulphur: so that it is not surprising Sulphur should be separated from

Arsenic by its interposition. Yet there is an inconvenience attends the

use of it: for it hath a great affinity with the Arsenic also, and so

always retains some part thereof, which continues fixed with it. For

this reason care should be taken not to mix, with sulphurated Arsenic,

a greater quantity of Alkali than is necessary to absorb the Sulphur

it contains. Nothing, however, but experience and repeated trials

can teach us the exact quantity of Alkali that ought to be employed;

because the quantity of Sulphur that may be contained in yellow or red

Arsenic is indefinite.

The vessel ought to be tall, that the upper part of the head, where the

Arsenical particles condense, may be the less exposed to heat. Towards

the end of the operation the fire must be strongly excited, so as to

make the sand red-hot; because the last portions of Arsenic that rise

are strongly retained by the Fixed Alkali.

Arsenic that is grey or blackish may be depurated and whitened by the

same means; because a Fixed Alkali absorbs the phlogiston likewise with

great avidity. Mercury, as well as a Fixed Alkali, is an excellent

additament for separating Arsenic from Sulphur. If you will use it for

that purpose, reduce the sulphurated Arsenic to a very fine powder, by

rubbing it a long time in a glass mortar; when it is well pulverized,

let a few drops of Mercury fall upon it, by squeezing it through

chamoy, and continue the trituration. The yellow or red colour of

the Arsenic will insensibly change, and gradually grow darker as the

Mercury incorporates with it. When the Mercury is perfectly killed,

add a little more of it than you did the first time, and in the same

manner: continue to triturate till it disappear; and thus go on adding

more and more till the Mercury you add remain quick, and you can kill

no more of it. Neither the red nor the yellow colour will then appear

in the mixture; which will be grey, if it contain but a little Sulphur,

and black, if a great deal.

Put this mixture into a very tall glass cucurbit; fit on a blind-head;

set it in a sand-bath, and bury it in the sand as far as the contained

mixture reaches. Heat the vessels, and, during the whole operation,

keep up a degree of fire a little weaker than that required for

subliming Cinabar. White Arsenical Flowers will adhere to the upper

part of the head, amongst which will be some beautiful crystals of

Arsenic; and underneath them you will find some Cinabar sublimed, but

not entirely free from Arsenic. If you desire to have your Cinabar and

your Arsenic purer, and more unmixed with each other, separate the

upper sublimate, which is Arsenical, from the lower, which consists

chiefly of Cinabar. Powder each of them coarsely, and sublime them

separately each in a different cucurbit.

On this occasion the Mercury separates the Sulphur from the Arsenic,

because it hath a greater affinity than Arsenic with that mineral. It

is not the only metallic substance of this character: for, as hath

been shewn, there are several others that have a greater affinity

than Mercury with Sulphur, being able to decompose Cinabar by their

interposition. Yet those metallic substances must not be substituted

for Mercury in the present operation: because there is none of them

but hath at the same time a very great affinity with Arsenic, or even

as strong an one as they have with Sulphur; whereas Mercury will by no

means unite with Arsenic.

This method of separating Arsenic from Sulphur hath two advantages over

that in which a Fixed Alkali is the medium. The first is, that by this

means all the Arsenic contained in the mixture is extracted out of it;

and the second, that, as Mercury doth not absorb Arsenic, we are not

put to the trouble of groping out, as it were, by trials the quantity

necessary to be added; and that, though more be added than is necessary

to absorb all the Sulphur, it will be of no prejudice to the operation.

But then it is attended with the inconvenience of being much more

tedious and more laborious than the other. For, in the first place, it

requires previously a very tiresome trituration, in order to procure an

union between the Sulphur and the Mercury, and so to form an Æthiops;

without which the Mercury and the sulphurated Arsenic will sublime

separately, so that no decomposition will be effected. Secondly, though

the Mercury be sufficiently united with the Sulphur of the Arsenic

by the long trituration that precedes the sublimation, this doth not

prevent, as we took notice above, the sublimed Arsenic and Cinabar

from being in some measure blended together; so that each requires a

second separate sublimation to render it very pure.

These inconveniencies cause a Fixed Alkali to be used preferably to

Mercury; the loss of a small quantity of the Arsenic, which remains

united with the Alkali, being little regarded; as that metallic

substance is neither scarce nor precious.

When Arsenic is united with a great quantity of Sulphur, it may be

freed from a part thereof without the intervention of any third body:

it is sufficient for the purpose to sublime it with a very gentle fire,

increased by insensible degrees. The most sulphureous part ascends

first; what rises afterwards is more Arsenical, and less sulphureous;

and the last flowers of all are pure Arsenic, or at least nearly so.

PROCESS III.

_To give Arsenic the Metalline Form. Regulus of Arsenic._

Take two parts of white Arsenic in fine powder, one part of the black

flux, half a part of Borax, and as much clean iron filings. Rub the

whole together, in order to mix them thoroughly. Put this mixture into

a good crucible, and over it put Sea-salt three fingers thick. Cover

the crucible; set it in a melting furnace; and begin with a gentle fire

to heat the crucible equally.

When arsenical vapours begin to ascend from the crucible, raise the

fire immediately so as to melt the mixture. Examine whether or no the

matter be thoroughly melted, by introducing an iron wire into the

crucible; and if the fusion be perfect, take the crucible out of the

furnace. Let it cool; break it; and you will find in it a Regulus of

a white and livid metallic colour, very brittle, scarcely hard, but

rather friable.

_OBSERVATIONS._

White Arsenic is, as hath been said, a metallic calx; and consequently

wants no more, in order to its acquiring the metalline properties, than

to be combined with the phlogiston: this is effected by the operation

before us.

The Iron added doth not serve here, as in making the Regulus of

Antimony, to precipitate the Regulus of Arsenic, by separating it from

some other substance with which it was united: on this occasion it does

nothing but join the Regulus of Arsenic, to which it gives solidity and

consistence. This is the only reason of its being made an ingredient

in the mixture; as the Regulus of Arsenic, without it, would have such

a tender consistence, that it could scarce be handled without falling

asunder into little bits. The Iron procures a further advantage in this

process; which is, that it prevents a great quantity of Arsenic from

being lost in vapours: for the Arsenic, with which it combines, is

restrained, and, in some measure, fixed by it.

Copper may be substituted for Iron, and procures the same advantages.

It is very necessary to remove the crucible from the fire as soon

as the matter is melted, and indeed to cool it as expeditiously as

possible, to prevent the Arsenic from flying off in vapours: for, when

once the Regulus is formed, the proportion of Arsenic, with respect

to that of the metal mixed with it, is continually lessening while it

stays in the fire; so that, after some time, there will be left in the

crucible, not a Regulus of Arsenic, but only Iron or Copper, alloyed

with a little Arsenic. On this occasion the Copper turns white, and

assumes the colour of Silver; but it soon tarnishes in the air.

It is easy to perceive, by what hath been said, that the Regulus of

Arsenic made according to this process is never pure, but contains

always a considerable quantity of Iron or Copper, whatever precautions

be used: but it is difficult to avoid this inconvenience, for the

reasons above assigned; and if we attempt to fuse Arsenic alone, with

reducing fluxes, the greatest part thereof is dissipated in vapours,

long before the very flux begins to melt: and that part of it, which

is found metallized, is not collected in one mass at the bottom of the

crucible, as in other metallic reductions; but in small particles,

dispersed and mixed among the scoriæ. There are nevertheless several

expedients for obtaining a Regulus of Arsenic absolutely pure, and

unalloyed with any metallic substance.

First: into a little low cucurbit, covered with a blind-head, put

Regulus of Arsenic made with Iron or Copper; set this cucurbit in a

sand-bath; heat it till the sand begins to grow red, and you will

see part of the Regulus sublime into the head, still retaining

its metalline splendour. The portion of Regulus thus sublimed is

pure Arsenic, or at least contains but a very small portion of the

adventitious metal, which may have been carried up with it. What is

left in the bottom of the cucurbit is the metal that was added, still

containing a little Arsenic, which continues obstinately fixed with it,

and which the violence of fire is unable to force away from it in close

vessels.

Secondly: mix your Arsenic in equal parts with the black flux; put

the mixture into such a cucurbit as that last mentioned; and apply to

it the strongest degree of heat that can be procured by a sand-bath;

arsenical flowers, of a blackish grey colour, will first sublime into

the head, and after them a Regulus of Arsenic of a white metalline

colour, which is pretty glossy, but tarnishes very soon in the air.

This Regulus hath no solidity: it is exceedingly friable; but it is

pure.

Thirdly: I have also made a Regulus of pure Arsenic by another method,

which produces a much greater quantity thereof, with a much smaller

degree of heat. For this purpose I powder the Arsenic, and mix with it

any Fat Oil; so that the mixture may be like a liquid paste: this paste

I put into a little phial of thin glass, like one of those used by

apothecaries; I set this phial in a sand-bath, and gradually heat it,

till the bottom of the pot containing the sand begin to be red. Part of

the Oil first rises out of the phial in vapours, which must be suffered

to pass off. After this the upper part of the phial is gradually lined,

on the inside, with a glittering metallic crust, which makes it look

like a quick-silvered glass. This crust is the Regulus of Arsenic. When

it begins to sublime, the mouth of the phial must be slightly stopped

with a bit of paper, and the heat increased a little, till you see that

nothing more rises.

If you break the bottle after the operation, you will find its upper

part crusted over with a coat of Regulus, thicker or thinner in

proportion to the quantity of Arsenic employed. The Regulus is in a

mass, of a beautiful brilliant colour, which to me seems to stand the

air better than that of any Regulus made by other methods; probably

because of the great quantity of fat matter with which it is united,

and by which it is defended.

This Regulus of Arsenic is absolutely pure, and a much greater quantity

thereof is obtained, by this method, than by treating it with the black

flux; because the Arsenic is much sooner and more easily combined

with the inflammable matter: and hence it comes to pass that part of

the Arsenic doth not rise at first in grey flowers, as in operating

with the black flux. Moreover, by our process, all the Arsenic is

sublimed in Regulus: whereas, when the black flux is employed, a pretty

considerable part of the Arsenic unites with the alkaline part of the

flux, and remains fixed therewith. In our operation there is nothing

left at the bottom of the phial, except an oily, light, but very fixed

coal.

Regulus of Arsenic, in whatever manner made, may be easily reduced

into white, crystalline Arsenic, by the means of a Fixed Alkali, or

of Mercury, applied in the same manner as for separating Arsenic from

Sulphur.

PROCESS IV.

_To distil the Nitrous Acid by the interposition of Arsenic. Blue_ Aqua

Fortis. _A new Neutral Salt of Arsenic._

Pulverize finely any quantity you please of refined Salt-petre. Mix

it accurately with an equal weight of white crystalline Arsenic, well

pulverized, or else with very white and very fine flowers of Arsenic.

Put this mixture into a glass retort, leaving one half of it empty.

Set your retort in a reverberating furnace; apply a receiver having a

small hole drilled in it, and containing a little filtered rain-water;

lute the receiver to the retort with stiff lute. Begin with putting two

or three small live coals in the ash-hole of the furnace, and replace

them with others when they are ready to go out. Go on thus warming your

vessels by insensible degrees, and put no coals in the fire-place,

till the retort begin to be very warm. You will soon see the receiver

filled with vapours of a dark-red, inclining to a russet colour. With

a bit of lute stop the little hole of the receiver. The vapours will

be condensed in the water of this vessel, and give it a very fine blue

colour, that will grow deeper and deeper as the distillation advances.

If your Salt-petre was not very dry, some drops of Acid will also come

over, and falling from the nose of the retort mix with the water in

the receiver. Continue your distillation, increasing the fire little

by little as it advances, but exceeding slowly, till you see that when

the retort is red-hot nothing more comes off; and then let your vessels

cool.

When the vessels are cold, unlute the receiver, and, as expeditiously

as you can, pour the blue _aqua fortis_ it contains into a crystal

bottle; which you must seal hermetically, because this colour

disappears in a short time when the liquor takes air. You will find in

the retort a white saline mass moulded in its bottom, and some flowers

of Arsenic sublimed to its upper cavity, and into its neck.

Pulverize the saline mass, and dissolve it in warm water. Filter the

solution, in order to separate some arsenical parts that will be left

on the filter. Let the filtered liquor evaporate of itself in the

open air; when it is sufficiently evaporated, crystals will shoot in

it representing quadrangular prisms, terminated at each extremity

by pyramids, that are also quadrangular. These crystals will be in

confused heaps at the bottom of the vessel: over them will be other

crystals in the form of needles; a saline vegetation creeping along the

sides of the vessel; and the surface of the liquor will be obscured by

a thin dusty pellicle.

_OBSERVATIONS._

Arsenic, as we took notice in our Elements of the Theory, besides the

properties it hath in common with metallic substances, possesses others

also in common with saline substances. One of the most remarkable among

the latter is that of decomposing Nitre; of expelling the Acid of that

Salt from its Alkaline basis, assuming its place, and forming with that

Alkali a Neutral Salt, which is very soluble in water, and shoots into

regular crystals.

To inquire into what passes in the decomposition of Nitre by Arsenic,

and into the new Salt resulting from thence, was the design of the

first Memoir given in by me to the Academy of Sciences on this

subject, and from that the present process is copied. Though the whole

quantity of Arsenic prescribed in the process doth not enter into the

composition of the new Neutral Salt, seeing some of it sublimes in

flowers, that quantity must not therefore be thought too great: for

we see, on the other hand, that part of the Nitre is not decomposed.

The needle-like Salt is no other than Nitre that hath not suffered any

decomposition, and actually deflagrates on live coals like common Nitre.

The precaution of putting some water in the receiver is absolutely

necessary, to condense the nitrous vapours that rise in the

distillation: for they are so elastic, so volatile, so dephlegmated,

that a very small part of them will otherwise be condensed into a

liquor, while the rest will remain in the form of vapours, to which

vent must be given through the small hole in the receiver, as without

that they will burst the vessels with impetuosity: and consequently

scarce any Acid will be obtained; especially if the Nitre employed be

very dry, as it must be to be reducible into a fine powder.

The blue colour communicated by the Nitrous Acid to the water is very

remarkable. The cause that produces this colour is not yet known.

Though the Acid is, on this occasion, mortified by a great quantity of

water, yet, when it rises out of the retort, it is so concentrated as

to form, even with that water, if too much be not put in, a most active

and even smoking _aqua fortis_.

It is necessary in this operation, and more so than in any other, to

warm the vessels gradually, and to proceed exceeding slowly; otherwise

the artist runs the risque of seeing his vessels burst to pieces with

violence, and with great danger to his person: for Arsenic acts on

Nitre with incredible vivacity; insomuch that, if a mixture of Nitre

and Arsenic be heated to a certain degree, the Nitre is decomposed

almost as rapidly, and with as great an explosion, as when it is made

to fulminate with an inflammable matter. In short, the appearances are

such, that one would be almost induced to think the Nitre really takes

fire on this occasion: though it be only decomposed just as it is by

the Vitriolic Acid.

The solution of the _caput mortuum_ of this distillation contains, at

the same time, several sorts of Salts: to wit, 1. the Neutral Salt

of Arsenic, formed by the union of the Arsenic with the basis of the

Nitre; this shoots into the prismatic crystals above-mentioned: 2. some

Nitre that hath not been decomposed; this forms the needles and part

of the vegetations: 3. a small portion of Arsenic, that is known to be

soluble in water; this forms the thin dark pellicle that covers the

surface of the liquor when it begins to evaporate.

For the properties of this new Neutral Salt of Arsenic you may consult

what we have said thereupon in our Elements of the Theory, and in the

Memoirs of the Academy of Sciences.

PROCESS V.

_To alkalizate Nitre by Arsenic._

Melt in a crucible the Nitre you intend to alkalizate. When it is

melted, and moderately red, project upon it two or three pinches of

pulverized Arsenic. A considerable effervescence and ebullition

will immediately be produced in the crucible, attended with a noise

like that which Nitre makes, when it detonates with an inflammable

matter. At the same time a thick smoke will rise, which at first will

smell like garlic, the odour peculiar to Arsenic; it will also smell

afterwards like Spirit of Nitre. When the effervescence in the crucible

is over, throw again upon the Nitre as much pulverized Arsenic as

you did the first time; and all the same phenomena will be repeated.

Continue thus throwing in Arsenic in small parcels, till it produce no

more effervescence; taking care to stir the matter at every projection

with an iron wire, the better to mix the whole together. Then increase

your fire, and melt what remains. Keep it thus in fusion for a quarter

of an hour, and then take the crucible out of the fire. It will contain

a Nitre alkalizated by Arsenic.

_OBSERVATIONS._

This operation, as well as the preceding one, is a decomposition of

Nitre by Arsenic; yet the result is very different: for, instead of a

Salt capable of crystallizing, and discovering no tokens either of Acid

or Alkali, we obtain, on this occasion, only a Salt that runs into a

liquor by the moisture of the air, doth not crystallize, and hath all

the properties of an Alkali.

These differences arise only from the different manner in which the

decomposition of the Nitre, and the union of the Arsenic with the basis

of that Salt, is brought about. When the Nitrous Acid is distilled by

the interposition of Arsenic, with a view to obtain the Arsenical Salt,

the operation must be performed in close vessels; no greater degree of

heat must be applied to the mixture than is necessary for enabling the

Arsenic to act; and that heat must be administered very slowly and by

insensible degrees. But, when the business is to alkalizate Nitre by

the means of Arsenic, the operation is performed in a crucible, in a

naked fire, with a strong degree of heat, and that suddenly applied.

The violence of the heat, the suddenness with which it is applied, the

vivacity wherewith the Arsenic unites with the basis of the Nitre; and,

still more than all these, the free access of the air, occasion the

greatest part of the Arsenic, which at first combines with the basis of

the Nitre after having expelled its Acid, to be presently carried off

and dissipated in vapours; and consequently the basis of the Nitre,

not being sufficiently saturated, discovers its Alkaline properties.

I say, the concurrence of the air contributes, still more than all the

rest, to separate the Arsenic from the Alkaline basis of the Nitre;

experience having taught me that the Neutral Salt of Arsenic is not

to be alkalizated by the most violent force of heat, as long as it

continues in close vessels, and the external air hath no communication

with it; but that some of the Arsenic contained in that Salt is

dissipated, by exposing it to a strong heat in open vessels.

The tumult and effervescence that arise, when Arsenic is projected on

Nitre fused in a crucible, are so considerable, and so nearly resemble

the detonation of Nitre with an inflammable matter, that we should

be tempted to think, if we trusted appearances only, that Arsenic

furnishes a combustible matter, and that the Alkalization of the Nitre

is effected, on this occasion, in the same manner as when it is fixed

by charcoal: but, by examining attentively what passes, we easily

discover that there is no inflammation at all, and that the Nitre is

alkalizated in the manner and by the means above pointed out.

The first vapours that rise, when Arsenic is projected on Nitre, are

purely arsenical; and, if any cold body be put in their way, they

adhere to it in the form of flowers. These vapours are actual particles

of Arsenic, carried up by the heat before they could come to act on the

Nitre; but they are soon after mixed with Nitrous vapours, consisting

of the Acid of the Nitre, which the Arsenic expels from its basis as

fast as it comes to act on that Salt.

The nearer you come to the end of the operation, the more does the

matter in the crucible lose of its fluidity, though an equal fire

be constantly kept up in the furnace. At last it becomes quite like

a paste, and the fire must be made much stronger to put it again in

fusion. The reason of this is, that Nitre when alkalizated is much less

fusible than when it is not so. The case is the same when this Salt is

alkalizated by deflagration.

Though the Nitre, when alkalizated, makes no more effervescence with

Arsenic, and though, when kept in fusion, it emits no more arsenical

vapours, it doth not thence follow that it is a pure Alkali, and that

it contains no Arsenic: it still contains a large quantity thereof,

but so strongly united that the force of fire is not able to separate

them; which hath led some authors to give this Salt the title of _Fixed

Arsenic_.

The existence of Arsenic in this saline compound is easily discovered,

by fusing it with metallic substances, on which it produces the same

effects as Arsenic.

With solutions of metals in the Acids, it also presents almost the same

phenomena as the Neutral Salt of Arsenic. Particularly it precipitates

Silver dissolved by the Nitrous Acid in a red powder, as that Salt

does; and the differences observed between the precipitations made by

our new Neutral Salt of Arsenic, and those made by Nitre alkalizated

with Arsenic, can be attributed only to the alkaline quality of the

latter. See the Memoirs of the Academy for 1746.

[Illustration: Decorative Scroll.]

PART II.

OF VEGETABLES.

SECTION I.

_Operations on unfermented Vegetables._

CHAP. I.

_Of the_ SUBSTANCES _obtained from_ VEGETABLES _by_ EXPRESSION _only_.

PROCESS I.

_To express and depurate the Juice of a Plant, containing its Essential

Salt. The Crystallization of that Salt._

Before sun-rise gather a good quantity of the plant from which you

design to express the juice, in order to obtain its Salt. Wash it well

in running water, to clear it of earth, insects, and other adventitious

matters. Bruise it in a marble mortar; put it into a bag of new,

strong, thick linen cloth; tye the bag tight, and commit it to a press.

By pressing it strongly you will squeeze out a great quantity of green,

thick juice, which will have the same taste as the plant. Dilute this

juice with six times as much pure rain-water, and filter it repeatedly

through a woollen bag, till it pass clear and limpid. Evaporate the

filtered juice with a gentle heat, till it be almost as thick as before

it was mixed with water. Put this inspissated juice into a jar, or

other vessel of earth or glass; on its surface pour olive oil to the

depth of a line, and set it in a cellar. Seven or eight months after

this, pour off gently the liquor contained in the vessel, the inside

of which you will find covered with a crystallized Salt. Separate the

crystals gently; wash them quickly with a little fair cold water, and

dry them: this is the Essential Salt of the plant.

_OBSERVATIONS._

Every plant is not equally disposed to yield its Essential Salt,

by the method here proposed. Succulent vegetables only, whose

juices are aqueous and not too viscous, are fit for this purpose.

Such, for example, as sorrel, brook-lime, succory, fumitory,

water-cresses, plantain, &c. An Essential Salt cannot be procured

from those that yield thick, viscid, mucilaginous juices, such as

the seeds of flea-wort; unless their juices be previously attenuated

by fermentation, and that viscosity destroyed which obstructs the

Crystallization of this Salt.

Nor can the Essential Salt be obtained in any quantity from vegetable

matters abounding in Oil. Most kernels and seeds are of this sort:

they all contain a great quantity of fat oil, which so entangles and

clogs this Salt, that the particles thereof cannot shoot away from the

tenacious juices into crystals.

The same is to be said of dry aromatic plants; because they contain

much essential oil, or resinous matters that produce the same effect.

It is true the Essential Salt itself contains a certain portion of

oil; for it is no other than the Acid of the plant incorporated and

crystallized with part of its oil and of its earth: but then the oil

must not be in too great a quantity: because it sheaths the Acid,

renders it clammy, as it were, and hinders it from extricating itself,

so as to be able to exert its qualities, and appear in the form of Salt.

The plants, from which you intend to extract this Salt, should be

gathered in the morning before sun-rise; because they are then most

succulent, not being yet dried up or withered by the heat of the sun.

The juice of plants obtained by expression is very thick; because it

contains many particles of the bruised plant, that are unavoidably

squeezed out along with it. In order to clear it of these superfluous

parts, it is proper to filter it; but as that would be difficult, on

account of the thickness of the juice, it must be thinned, by diluting

it with a quantity of water, sufficient to give it the requisite degree

of fluidity.

Instead of thus diluting the expressed juice, the plant may be ground

with water, before it is put into the press: it will by this means

furnish a more fluid juice, that will easily pass through the filter.

This method may be employed with success on dry plants, or such as are

not very succulent. For this operation rain-water is to be preferred

to any other; because it is the purest: for all waters that have run

some time through the earth, or on its surface, are to be suspected of

containing some saline or selenetic matter, which would mix with and

deprave the Essential Salt.

The juice of the plant, when diluted with the quantity of water

sufficient to facilitate its filtration, is too aqueous to let the Salt

it contains unite into crystals: it must therefore be evaporated, till

it hath recovered a somewhat thicker consistence. The heat applied for

that purpose must be gentle; lest the acid and oily parts, that are to

form the Salt, be spoiled or dissipated, as they are not very fixed. In

summer, the heat of the sun is sufficient to effect this evaporation:

but if you make use of this method, the juice to be evaporated must be

put into several broad flat pans; that, a larger surface being exposed

to the action of the air and sun, the evaporation may be the sooner

completed: for if the juice should continue too long in the degree of

heat requisite for its evaporation, it might begin to ferment; which

would be very detrimental.

The oil poured on the liquor prevents its fermenting, putrefying,

or growing mouldy, during the long space of time required for the

crystallization of the Essential Salt.

These Salts are excellent medicines, being endued with the same virtues

as the plants from which they were obtained.

They cannot be procured from plants by distillation, though they

consist in a great measure of volatile principles: nor are they

obtainable by any other process that requires much heat; because

they are easily decomposed, and the fire changes their natures

entirely. The oily Acids extracted from plants by distillation do not

crystallize, and always have an empyreumatic acrimony, that makes

them very different from the Essential Salts, which are very mild and

saponaceous.

PROCESS II.

_To draw the Oils out of Kernels, Seeds, and Fruits, by Expression._

Pound in a marble mortar, or grind in a mill, the kernels, seeds, or

fruits, out of which you intend to express the Oil. If your matters be

meagre, and grind to meal, suspend that meal in the steam of boiling

water, in order to moisten it a little, and then dry it.

Tye up your matter thus prepared in a new, strong, thick, canvass bag,

and put it into a press, between two iron plates previously heated in

boiling water: squeeze it strongly, and you will see the Oil run in

streams into the receiving vessel.

_OBSERVATIONS._

The Fat Oil of Plants is particularly found in kernels, seeds, and

some fruits; some kernels contain such a vast quantity thereof, that,

on being very slightly bruised in a mortar, they discharge it in great

abundance. Sweet and bitter Almonds, Walnuts, and Lint-seed, are all

of this kind; and require no other management but to be pounded and

pressed, to make them yield a great deal of Oil. But there are others

more meagre, that being ground produce an almost dry flower. In order

to facilitate the expression of the Oil out of such, they must be

expressed, when ground, to the steam of boiling water. For this purpose

the meal may be put into a fine sieve, and that suspended over a pan

half-full of water kept boiling on the fire. The ascending vapours

will moisten the flower, render it more unctuous, and facilitate the

expression of the Oil.

It is proper to dry it a little before it be put into the press,

that it may yield as little water as possible along with the Oil.

Nevertheless, so much water happens now and then to be left in it, that

some is expressed together with the Oil: but as oil and water do not

incorporate, they are easily separated after the operation is finished.

The extraction of the Oil is also greatly facilitated by heating the

plates, between which the oleaginous matters are squeezed: but they

must not be made too hot, if you mean to have a very mild Oil, designed

either for aliment or for medicine; such as the Oil of Olives, and that

of sweet almonds. For this reason the plates must be warmed in boiling

water only: if you heat them to a greater degree, you run the risk of

giving an acrimony to the Oils you express. But, when these Oils are

intended for other uses, the plates may be made hotter, because their

heat increases the yield of Oil.

It is remarkable, that all the Oils obtained by expression, with the

precautions above recommended, are constantly very mild; even though

the matters from which they are extracted be in themselves very acrid.

Mustard-seed, which is so acrid that it is even caustic, yields, by

expression, an Oil as mild as that of sweet almonds. But then the

kernels, seeds, and fruits, from which the Oils are extracted, must

not be old; because these Oils, which are perfectly mild when fresh

and new, become intolerably acrid when they grow old, and acquire this

acrimony even in the fruit itself; for it is observed that these fruits

turn rancid as they grow old.

The Fat Oils obtained by expression are used in medicine, both

internally and externally, as Lenitives and Emollients. Every body

knows the great use of Oil of sweet Almonds, in inflammatory distempers

of the breast and intestines. But it must be carefully noted, that

these Oils can produce no good effects, unless they be fresh expressed,

and from fruits, kernels, or seeds, that have not been long kept: for

they not only lose their lenient virtue by growing old, but they even

acquire an opposite quality, and contract such a sharp acrimony, that

far from procuring any salutary relief or mitigation to the inflamed

parts, they are capable of irritating and inflaming the sound.

It is therefore of the last importance to administer them only when

they are quite fresh: they ought never to be above two or three days

old. Those that are old are generally more limpid and transparent than

the fresh, which look a little more cloudy. The best way to distinguish

them is to taste them, and to try whether or no they leave any

sensation of rancidity on the palate and in the throat.

PROCESS III.

_To draw the Essential Oils of certain Fruits by Expression._

Take the rind of a Citron, Lemon, Orange, Bergamot-pear, or other fruit

of that kind; cut it in slices, and, doubling the slices, squeeze them

between your fingers, over against a polished glass set upright, with

its lower end in a vessel of earth or porcelain. Every time you squeeze

the peel in a new ply, there will squirt out of it several fine jets of

liquor, which, meeting with the surface of the glass, will be condensed

into drops, and trickle down in small streams into the recipient. This

liquor is the Essential Oil of the fruit.

_OBSERVATIONS._

No fruits but those of the kind above-mentioned will yield an essential

Oil by expression. The rind of the fruit is the reservoir of this Oil:

it is contained in little vesicles, which may be seen by the naked eye,

spread all over the surface of the peel, and which, bursting when the

peel is squeezed, discharge the Oil in the form of very fine slender

spouts. Every body knows, that these little oily streams instantly take

fire, when spirted through the flame of a candle: the Oil in this case

is entirely consumed.

The Essential Oil, thus obtained by expression, hath a very sweet and

most agreeable scent. It is in every respect the same as when it made

a part of the fruit that yielded it, seeing it hath not undergone the

action of fire. Yet this method, however good it may be, can hardly be

practised but in the countries where those fruits are in great plenty;

because we cannot by this means obtain any thing near the quantity of

Oil they contain.

This inconvenience may be remedied by rubbing the rind, which contains

the Essential Oil, on the surface of a sugar-loaf. The inequalities of

that surface produce the effects of a rasp, by tearing all the oily

vesicles. The Oil, which issues in abundance, is imbibed by the sugar

and moistens it. When the sugar is sufficiently impregnated therewith,

it may be scraped off with a knife, and put into a well-stopped bottle.

The sugar does not alter the nature of the Oil; which may be kept in

this manner for years, and used, though combined with the sugar, for

almost all the same purposes as when in a fluid state; that is, to

aromatize the several matters with which you incline to mix it. We owe

these observations to Mr. Geoffroy.

This experiment, in which the Essential Oil of a vegetable is obtained

by expression alone, and without the aid of fire, proves that the Oils

of this kind exist naturally in vegetables; and that the Oils of the

same kind obtained by distillation, as shall be shewn in its place, are

not the product of the fire. Essential Oils drawn by expression do not

very sensibly differ from those procured by distillation.

CHAP. II.

_Of the_ SUBSTANCES _obtained from_ VEGETABLES _by_ TRITURATION.

PROCESS I.

_To make the Extract of a Plant by Trituration._

Bruise the vegetable substance of which you intend to make the Extract;

or, if it be hard and dry, grind it to a powder: put the matter thus

prepared, together with seven or eight times as much rain-water, into

an earthen vessel; and into this vessel fit a churning staff, so that

it may be continually whirled round with a rotatory motion, by means

of a cord, a wheel, and a winch. Ply this machine for ten or twelve

hours; and then filter the liquor through two linen cloths spread on a

hair-sieve. Let your filtered liquor stand quiet for twelve hours more:

then pour it off by inclination from the sediment you will find at

bottom; and filter it a second time through a flannel bag.

Pour fresh water, but in a smaller quantity, on the mass left after

trituration with the machine. Triturate it again for four or five

hours. Treat the liquor of this second triture just as you did that

of the first, and mix them both together. Distribute all the liquor

you now have among a sufficient number of shallow earthen plates, and

evaporate it by a gentle warmth, such as that of the sun, or of a

vapour-bath, to the consistence of an Extract, or even to dryness, as

you think proper.

_OBSERVATIONS._

In trituration the water takes up, not only the Salts of plants, but

also a pretty considerable quantity of their oily and earthy parts,

which those Salts have rendered soluble therein, by communicating

to them a saponaceous and mucilaginous quality. After trituration,

therefore, nothing remains but the grossest particles of oil and

earth. Hence it is evident, that the water, in which plants have been

triturated, contains nearly the same principles as the juices of those

plants drawn by expression; and that it is also impregnated with their

Essential Salts: so that, by evaporating it to a due consistence, we

have a well made Extract of the triturated plant.

The Count de la Garaye, who hath long cultivated with great assiduity

those parts of Chymistry by which Medicine may be improved, hath made a

great number of experiments for obtaining from plants, by triture with

water, the matters in which their virtues chiefly reside, and hath also

published a work, entitled Hydraulic Chymistry, in which he gives a

particular account of all the processes for making such Extracts of the

chief mineral, vegetable, and animal substances, as are most frequently

used in the Practice of Physic. His way of evaporating, by a gentle

heat, the liquor containing the Extract of a triturated substance is a

very good one: for we know that heat, if but a very little too strong,

is capable of changing the natures of compound bodies, by disuniting

their principles, and exhaling some of them.

If all vegetable matters were fat and succulent, as most pot-herbs

are, triture would not be necessary for the making an Extract of them,

even without the help of fire. We should have nothing to do, for that

purpose, but to express their juices, as before, clarify them, and

evaporate with a gentle heat to the consistence of an Extract. But

many vegetable substances, such as woods, barks, roots, &c. are dry,

hard, and compact. These matters will not give out their Extract,

without such an application of water as shall dissolve their saline,

saponaceous, and mucilaginous parts. Now this must be effected either

by triture or by fire. Trituration has the advantage of procuring

Extracts, in which the principles are perfectly unaltered, and retain

the same proportions, with respect to each other, as in the plant: but

then it is attended with the inconveniencies of being very tedious,

troublesome, and chargeable. When we come to deliver the methods of

making extracts by decoction and by infusion, we shall see what are the

advantages and disadvantages of preparing Extracts by heat.

The matters, from which an extract is to be made by triture, must be

previously bruised and reduced into small parts, in order to facilitate

the action of water upon them. The several filtrations and decantations

here directed are intended to separate the grosser parts of the plant,

that were only suspended in the liquor, but not truly dissolved, by

means of the agitation and motion: for this reason also, the longer the

liquor is left to settle, the purer will the Extract be.

Though the plant be triturated the first time with a great deal of

water, and for a good while too, yet it is not by that means wholly

exhausted: M. de la Garaye therefore directs the remainder to be

triturated again with fresh water: but this second operation requires

only half the water used in the former, and need be continued only half

the time; the plant having been already opened by the former triture,

and having fewer parts to give out. It is better to add fresh water,

and triturate a second time, than to triturate but once, and for a

greater length of time: for when the water is impregnated with the

principles of the plant to a certain degree, it is less capable of

acting, and of dissolving more, than when it is pure.

As the water impregnated with the principles of the plant by triture

must be almost wholly evaporated, in order to bring those principles

nearer together, and that the whole may lie in the smallest compass

possible; and, moreover, as this evaporation must be effected by the

gentlest heat, it is necessary to spread the liquor so, by distributing

it among a great number of plates, that it shall be reduced in a manner

entirely to surface. By this means the Extract may be evaporated even

to dryness; and this is M. de la Garaye's practice. As the Extracts,

thus evaporated to dryness, cannot be taken up otherwise than in

little scales, the lower surfaces whereof, by adhering to the glazing

of the plate, are smooth and shining, they in some measure resemble a

crystallized Salt; which led M. de la Garaye into an error, and induced

him to give the title of Essential Salts to the Extracts prepared in

this manner. The Essential Salt is indeed contained in them; but still

they are only Extracts, as Mr. Geoffroy hath shewn, in a memoir on this

subject given in by him to the Academy; since, besides the Essential

Salt, they contain moreover, as was said before, a great deal of the

oil and earth of the matters from which they were extracted. This, in

the main, is no objection, but rather an advantage to them; considering

that such saline Extracts are, on that account, so much the more like

the substances from which they were obtained; especially with regard to

their medicinal properties.

PROCESS II.

_To extract from Seeds and Kernels, by Trituration, the Matter of

Emulsions._

Blanch the kernels of which you desire to make an Emulsion; put them

into a marble mortar; add a very little water; and pound them with a

wooden pestle. Continue pounding and triturating till the matter become

like a white paste. From time to time pour on it, by little and little,

more fair water warmed, still continuing the trituration; by which

means the paste will grow thinner. Go on thus till every particle of

your kernels be crushed to pap. Then add, still rubbing the mixture,

enough of water to make the whole an actual fluid; and you will have

a liquor of a dead-white colour, resembling milk. Strain it through a

clean linen cloth; it will leave on the filter some coarse parts, which

must be returned to those left in the mortar. Again triturate and rub

the remainder of the kernels, with the addition of water as before.

This second liquor will not be so white nor so rich as the former:

filter it in the same manner, and again grind with water the solid

parts remaining. In this manner proceed, repeatedly rubbing and adding

fresh water, till it appear no longer milky, but come off clear. The

white milky waters thus obtained go by the name of an _Emulsion_.

_OBSERVATIONS._

All the matters, from which a Fat Oil is obtainable by expression,

produce Emulsions when triturated with water.

An Emulsion consists chiefly of two substances. One of these is

mucilaginous, and soluble in water. This substance by itself would not

give a milky appearance to the Emulsion, which, with it alone, would

be limpid. The other is a Fat Oil, which of itself is not soluble in

water; but being divided by the means of trituration into very small

globules, it is dispersed through the whole liquor, and suspended

therein by the aid of the mucilaginous part. It is this oily part that

gives the Emulsion its dead-white, milky colour; because it is not

actually dissolved in the water, but only diffused through it.

If Oil be mixed with water in a phial, and the mixture strongly shaken

for some time, with a rapid and continued motion, the Oil will be

divided into a vast number of little globules, which intervening

between the parts of the water will destroy its transparency, and give

it a dead-white colour, like that of our Emulsion. But, as the Oil is

not so minutely divided by this means, as by triturating the matters

containing it; and again, there being no mucilage in this liquor, as

there is in Emulsions, the Oil soon separates from the water when it is

left at rest, re-unites into round globules, and these joining together

rise to the surface of the liquor, which then recovers its transparency.

The case is not exactly the same with Emulsions; but something like it

happens to them also. If they be left to stand quiet in a long bottle,

the liquor, which at first appeared homogeneous, separates into two

manifestly different parts. The upper part retains its dead-white

colour, but is thicker and more opaque; while the lower part becomes

perfectly transparent. This is the beginning of an entire separation

of the oily from the aqueous parts. The former, being the lighter,

ascend and gain the upper part of the liquor; while the lower, being

freed from that which obstructed its translucence, recovers its proper

limpidity: but the oily parts do not re-unite into masses large enough

to form one homogeneous whole, with the appearance and limpidness

of Oil; their being minutely divided and entangled in the mucilage

impeding their natural tendency.

Emulsions first begin to spoil, as they grow old, not by turning rancid

and acrimonious like the Fat Oils drawn by expression, but by turning

sour; which is owing to the great quantity of mucilage they contain.

As there is a Fat Oil in their composition, they have the same virtues

with that sort of Oil; but they are, moreover, incrassating, cooling,

and emollient; qualities which render them extremely useful in acute

and inflammatory disorders. They grow sour in a very short time,

especially in the heat of summer; nay, they sometimes do so in two

hours: and therefore they ought to be prepared from time to time as

they are to be used.

The matter that is left when all the substance of the Emulsion is

extracted, and from which the water comes off clear and limpid, is

scarce any thing but the earthy part of the seed or kernel that was

triturated; which, however, still retains a portion of tenacious and

gross Oil, adhering to it so firmly as not to be separable by water.

The chyle and milk of animals resemble an Emulsion in several respects,

and particularly in their dead-white colour; which arises, in the same

manner, from the very minute particles of Oil contained in them, and

distributed through an aqueous gelatinous fluid, but not dissolved

therein. In general, whenever any Oil of any kind happens to be lodged

in this manner between the parts of an aqueous liquor, it always makes

the whole of an opaque white: for Oil will not mix with water, so as to

produce a liquor that shall appear homogeneous and transparent, unless

it be intimately dissolved in the water; which cannot be effected but

by means of an union previously contracted between it and some saline

matter: as is the case of mucilages, certain saponaceous matters, and

some other combinations of which we shall have occasion to treat in the

sequel.

The methods we have hitherto proposed, for extracting from vegetable

substances all that they will yield without the assistance of fire, are

not capable of analyzing those substances accurately, as you may have

observed; since by expression and trituration we obtain only the liquid

parts, impregnated indeed with almost all the principles of plants,

which, however are still combined with each other, and barely separated

from the grossest earthy and oily parts. We must therefore necessarily

have recourse to a more effectual expedient for carrying our analysis

further. This expedient consists in making them undergo the action of

fire, successively graduated, from the gentlest to the most violent

heat.

But, before we enter on this Analysis of Vegetables, it is proper to

describe the different operations that may be performed on Oils, the

only pure principle we have been able to obtain without the help of

fire. As we shall have occasion, when we come to treat of the analysis

of plants by fire, to say a great deal more concerning Essential

Oils, we reserve till then what relates to the operations that may be

performed on them; and confine ourselves here to the operations on Fat

Oils.

CHAP. III.

_Of_ OPERATIONS _on_ FAT OILS.

PROCESS I.

_To attenuate Fat Oils, and change their Nature, by exposing them to

the Action of Fire, and distilling them._

Mix thoroughly three or four pounds of any Fat Oil whatever, with

twice its weight of lime flaked in the air. Put this mixture into a

large earthen retort, leaving a third part of it empty. Set it in a

reverberating furnace, and lute on a receiver. Heat the vessel with a

very gentle fire. A little phlegm will rise first, and will soon be

followed by an Oil that will fall in drops from the nose of the retort.

Continue the distillation very slowly, till you perceive the Oil that

comes over begin to be not quite so fluid as before, but rather a

little thicker.

Then unlute your receiver, and put another in its place. Continue the

distillation, increasing your fire by degrees. The Oil that comes over

will grow thicker and thicker, its fluidity will decrease, and it will

acquire a dark-brown colour, which at last will become blackish. The

Oil will then be very thick. Push the operation till nothing more will

come off, though the retort be red-hot. During the whole time this

distillation lasts, there rises a good deal of water, in company with

the Oil. Keep the second thick Oil by itself.

Mix the Oil that came over first, in this operation, with an equal part

of fresh lime flaked in the air. Put the mixture into an earthen or

glass retort, of a size so proportioned to the quantity, that a third

part thereof may remain empty. Distil as before. The same phenomena

will appear: a clear Oil will first come over, and be succeeded by one

a little thicker. Then shift your receiver, and distil off all the

rest of the Oil with an increased fire. The first Oil obtained by this

second distillation will be clearer and thinner than that of the first

distillation; and the second Oil will not be so thick, nor of so deep a

colour as before.

Distil over again, in the same manner, the thin Oil of this second

distillation, and go on thus repeatedly distilling, till the first

clear oil come over with a degree of heat not exceeding that of boiling

water. Then, instead of mixing your Oil with lime, put it with some

water into a glass retort, or into a body with its head fitted on, and

distil it, keeping the water just in a simmer. Your Oil will be more

and more attenuated, and, after being thus distilled twice or thrice

with water, will be so limpid, so thin, and so clear, that you will

scarce be able to distinguish it from water itself.

_OBSERVATIONS._

Fat Oils, which are naturally mild, unctuous, inodorous, or have at

most a scarce perceptible smell, resembling that of the fruit or kernel

from which they were extracted, change their natures totally when

exposed to the action of fire. If they be but heated so as to boil,

they become acrid, lose much of their unctuosity, and acquire a very

pungent odour. From several analogies, and by several experiments,

recited in a Memoir on Oils which I read to the Academy, I shewed that

these alterations of Fat Oils are produced by the fire's extricating an

Acid in them, which before lay concealed and inactive. What I advanced

on this subject may be seen in the Memoirs of the Academy for 1745, and

in my Elements of the Theory of Chymistry. I shall take occasion to add

something more, in my Observations on the following process, by which

these Oils are combined with Acids. In this place I shall only examine

what passes in the repeated distillations they are here made to undergo.

Fat Oils do not rise in distillation without a degree of heat greater

than that of boiling water; and therefore they must be distilled in

a sand-bath, or with a naked fire. We prefer the latter method, for

reasons elsewhere assigned, and chiefly because the operator is more

master of his fire; it being absolutely necessary, in this operation,

that he have it in his power to suppress it in an instant, when he

finds it too strong: for, in such a case, it will impetuously raise

the thin Oil mixed with the thick; nay, the whole will be burnt, as

it were, to a coal, if a degree of fire ever so little too strong

be kept up but for a few moments. When this accident happens, it is

always predicted by a great quantity of white vapours ascending with

impetuosity out of the retort, and by drops of Oil following each other

very fast, that are scarce limpid at first, and soon become of a dark

colour. All this may be prevented by distilling very slowly, and with

great patience.

Fat Oils may be distilled and attenuated without any additament: but

then the operation, which is tedious and troublesome enough, even when

lime is used, as appears from our description of the process, would be

much more so if the Oil were distilled alone, without the addition of

any thing to divide it, spread it, and enlarge its surface.

Lime is one of the best additaments that can be employed on this

occasion; not only because it procures the advantages just mentioned,

but also by reason that, being an absorbent of fat matters, it unites

with the grosser parts of the Oil, retains them, and so allows the

thinnest and lightest parts to be readily separated from the rest. By

this means it greatly expedites the operation: and, the more of it is

added, with respect to the oil, the sooner is a considerable quantity

of thin limpid Oil obtained: and this is the reason of our directing

a double quantity of lime to be mixed with the Oil in the first

distillation.

Lime slaked in the air is employed preferably to quick-lime; because

it is naturally divided into a very fine powder, and capable of mixing

perfectly with all sorts of matters.

The water that first appears in the distillation comes from the

lime: it is part of the humidity which the lime had imbibed from

the air. This water continues to rise with the Oil during the whole

distillation, according as the degree of heat is increased: and, if the

distillation be finished by keeping the retort red-hot for some time

after all is come over, the lime in it will have a greyish cast, and,

when water is poured on it, grow almost as hot as quick-lime.

If you resolve to carry on these distillations of a Fat Oil, till it

becomes as light as an Essential Oil, it is necessary to begin with

a pretty large quantity thereof, as three or four pounds: for the

quantity of the Oil is considerably lessened by every distillation; not

only because the thickest and grossest part is separated from it every

time; but also because a portion of the Oil remains so strongly united

with the lime, that the force of fire is not able to separate them.

Moreover, there is reason to believe that some of it is decomposed

every time it is distilled.

If Oil be distilled by itself, the thickest and heaviest part remains

charred, as it were, in the retort, the inside of which is lined with a

crust of coal, that is to the last degree fixed: this therefore always

occasions a diminution of the Oil.

A Fat Oil must be distilled eight or nine times, even with lime, before

it become as light as an Essential Oil, and capable of rising wholly

with the heat of boiling water: by that time therefore it must be

considerably diminished; and if, at least, the quantity prescribed be

not taken at first, there will scarce remain a few ounces capable of

being distilled with water.

The portion of thick heavy Oil, obtained in the several distillations,

may, if you will, be rectified again. For this purpose you must mix it

with fresh lime, and distil it as you did the clear Oil. A portion of

this also will be attenuated, and come over first. Thus all the Fat

Oil may be subtilized by the action of fire; an absolutely charred

black part excepted, that remains fixed, and appears susceptible of no

change, but by burning it in the open air, and thereby reducing it to

ashes, from which a little Fixed Alkali may be obtained. In this fixed

part of the Oil the acid and earthy parts are combined therewith, in a

greater proportion than they ought to be in pure Oil.

The portion of Oil that hath become light and thin is nothing but the

purest oily part, separated from the gross acids, and from a certain

quantity of earth, which made it thick and heavy. This Oil resembles

the Essential Oils in lightness, fluidity, and a penetrating agreeable

odour: it dissolves in Spirit of Wine. We shall have occasion in the

sequel to enlarge further on the qualities of the several sorts of

Oils, and their solubility in Spirit of Wine, when we come to treat of

Ardent Spirits and of Æther.

PROCESS II.

_To combine Fat Oils with Acids. The Decomposition of this Combination._

Put any Fat Oil whatever into a glass bason, and set it in a sand-bath

very moderately heated. Pour on this Oil an equal quantity of

concentrated Oil of Vitriol, which will immediately dissolve it with

violence; a considerable ebullition and effervescence will arise,

attended with great heat, and a prodigious quantity of black, thick

vapours, in which may be easily perceived the smell of burnt Oil,

together with that of a Sulphureous Acid. The mixture will become of

a deep-red, black, and thick. Stir it with a small stick, till you

observe that all is quiet.

_OBSERVATIONS._

The Vitriolic and Nitrous Acids unite with Fat Oils, and dissolve

them with violence; but these Acids must be sufficiently strong and

concentrated, otherwise they will not act upon the Oils. The Vitriolic

Acid, in particular, dissolves them pretty thoroughly. If hot water

be poured on the mixture described in our process, this water will

become cloudy and milky, by dissolving some of it: so that Oils may be

rendered soluble in water by the means of Acids. Spirit of Wine, which

doth not attack Fat Oils in their natural state, unites perfectly with

them, and makes a clear limpid solution of them, when they are thus

combined with Acids.

The Acids also suffer a considerable alteration by contracting an union

with Oils. They become much milder, and lose almost all their strength.

If the mixture described in the process be distilled, there will come

over a great quantity of an empyreumatic acidulated phlegm, that

smells strong of Sulphureous Spirit; an Oil thinner than the original

saponaceous mixture; a weak Oily Acid, and a very thick, black Oil. If

the fire be made very strong, when the Oil ceases to rise, it sometimes

happens that a little Sulphur sublimes into the neck of the retort.

By this analysis it appears, that the strong concentrated Acid, which

was an ingredient in the combination, is not now to be found. The

Vitriolic Acid hath changed its nature, and is considerably weakened

by the union it hath contracted with the principles of the Oil. The

aqueous part of this latter substance weakens the other, and loads it

with phlegm; the inflammable part thereof renders it sulphureous, and

even converts it into Sulphur.

Hence it follows, that same part of the Oil is decomposed, by the

union it contracts with the Vitriolic Acid; for its phlogiston and its

aqueous principle cannot be disunited, so as to form a Sulphureous

Spirit, or an actual Sulphur, and an aqueous Acid, without the

decomposition of a certain quantity of the Oil, in proportion to the

two disjoined principles. Another portion of the Oil remains united

with the Vitriolic Acid, without suffering any decomposition, and

communicates to that portion of the Acid, with which it is combined,

a somewhat saponaceous quality, which makes it resemble the Vegetable

Acids.

Thus we see, that when the Vitriolic Acid and a Fat Oil are combined

together, they both suffer considerable changes; the Acid by the new

alliances into which it enters, and the Oil by the decomposition it

undergoes. In consequence hereof a much smaller quantity of Oil is

obtained, by decompounding this combination, than was at first put in.

If the Oil abstracted by distillation be combined again with a fresh

quantity of the concentrated Acid, the same effects will again follow;

and by this means any quantity of Oil at pleasure may be entirely

decomposed. This single experiment affords an evident proof of many

important truths advanced in our Elements of the Theory.

Spirit of Nitre likewise dissolves expressed Oils. With Oil of Olives

it forms a white paste, resembling a fine pomatum. This compound is

perfectly soluble in Spirit of Wine. The Acid must be very strong and

smoking to unite with this, or with any other Fat Oil: but it dissolves

some of them with more rapidity than others; in which number is the Oil

of Walnuts. It acts on these Oils with so much vehemence that it burns

them, in some measure, making them black and thick.

PROCESS III.

_To combine Fat Oils with Fixed Alkalis. Hard and soft Soap. The

Decomposition of Soap._

Take a lixivium of Alicant kelp made more caustic by lime, as we shall

shew when we come to speak of Alkalis. Evaporate this lye till it be

capable of bearing a new-laid egg. Divide it into two parts; and to one

of these put just water enough to weaken it so, that a new-laid egg

will not swim in it, but fall to the bottom. With the lye thus weakened

mix an equal quantity of fresh-drawn Olive Oil. Stir and agitate the

mixture well, till it become very white. Set it over a gentle fire,

and continue stirring it incessantly, that the two ingredients of

which it is compounded may gradually combine together, as part of the

water evaporates. When you perceive they begin to unite, pour into the

mixture thrice as much of the first strong lye as you took of Olive

Oil. Continue the coction with a gentle fire, always stirring the

matter, till it becomes so thick that a drop of it fixes, as it cools,

into the consistence that Soap ought to have. By dissolving a little

of this Soap in water, you will discover whether or no it contains

more Oil than ought to be in the composition. If it dissolves therein

wholly and perfectly, without the appearance of the least little drop

of Oil floating on the water, it is a sign that it doth not contain

too much Oil. If, on the contrary, you perceive any of these little

globules, you must pour into the vessel, containing your matter, a

little more of the strong lye, to absorb the redundant Oil. If there be

too much of the Alkali it may be discovered by the taste. If the Soap

leave on your tongue the sensation of an Alkaline Salt, and produce an

urinous savour, it is a sign that there is too much Salt in proportion

to the Oil. In this case a little Oil must be added to the mixture, to

saturate the super-abundant Alkali. An excess in the quantity of Alkali

discovers itself likewise by the Soap's growing moist in the air, on

being exposed to it for some time.

_OBSERVATIONS._

Fixed Alkalis, even when resolved into a liquor, that is, when loaded

with much water, unite easily with Fat Oils, as appears from the

experiment just recited, and require but a moderate heat to perfect

that union. This combination may even be completely effected without

the aid of fire, and by the heat of the sun only, provided sufficient

time be allowed for that purpose; as Mr. Geoffroy found upon trial. It

only requires the mixture of the Oil and Alkali to be kept five or six

days in digestion, and stirred from time to time. A lixivium of pure

Alkali, not acuated by lime, may also be used to make Soap: but it is

observed, that the combination succeeds better, and that the Alkali

unites sooner and more perfectly with the Oil, when it is sharpened by

lime.

The Oil is first mixed with a weaker and more aqueous lye, to the end

that the combination may not take place too hastily, but that all the

particles of the two substances to be compounded together may unite

equally. But as soon as the Alkali begins to dissolve the Oil gradually

and quietly, the dissolution may then be accelerated; and that is done

by adding the remaining lye, which is stronger and less diluted than

the other.

Soap made with Olive Oil is white, hard, and hath not a very

disagreeable smell: but as that Oil is dear, others, even the fat and

oils of animals, are sometimes substituted for it. The Soaps made with

most of these other matters are neither so hard, nor so white, as that

made of Olive Oil: they are called _Soft Soaps_.

Oils thus associated with Fixed Alkalis are by that means rendered

soluble in water; because the Alkaline Salts, having a great affinity

with water, communicate part thereof to the Oils with which they are

now incorporated. Yet the Oil is not for all that rendered thoroughly

miscible with water, or perfectly soluble therein; for the water in

which Soap is dissolved hath always a milky cast: now there is no other

criterion of a perfect solution but transparency.

Alkalis also lose part of their affinity with water, by the union

they thus contract with Oils: for, when the combination is properly

made, they no longer attract the moisture of the air, nor doth water

dissolve them in such quantities as before. The composition of Soap is

plainly a saturation of an Alkali with an Oil; and, in order to make

perfect Soap, we are forced, as was said in the process, to grope, in a

manner, by repeated trials, for this point of saturation; just as when

we prepare a Neutral Salt by saturating an Alkali with an Acid. The

union which the Oil contracts with the Alkali makes it lose, in part,

the readiness with which it naturally takes fire; because the Salt is

not inflammable: the water also, which enters in pretty considerable

quantities into the composition of Soap, as we shall presently see,

contributes a good deal to hinder the accension of the Oil.

Soap may be decompounded either by distilling it, or by mixing it with

some substance that hath a greater affinity than Oil with Alkalis.

If we decompound it by distillation, a phlegm, or transparent spirit,

of a somewhat yellowish colour, first comes over. This liquor is the

aqueous part of the Soap, quickened by a little of its Alkali, which

gives it an acrid taste. It is followed by a red Oil, which at first

is pretty thin and limpid, but thickens as the distillation advances,

grows black, and has a very disagreeable empyreumatic smell. This Oil

is soluble in Spirit of Wine.

When the distillation is finished, that is, when the retort being kept

red-hot for some time will discharge no more, there is left in it a

saline mass; which is the Alkali of the Soap, crusted over with some

of the most fixed parts of the Oil, that are charred to a coal. This

Salt may be restored to the same degree of purity it had before its

combination with the Oil, by calcining it in a crucible with a naked

fire, that may consume this burnt part of the Oil, and reduce it to

ashes.

It is plain that the Oil contained in Soap is affected by distillation,

much in the same manner as that which we mixed with lime and distilled.

Mr. Geoffroy, by analysing Soap with care, discovered that two ounces

thereof contain ninety-six grains of Salt of kelp, freed from all Oil

and moisture; or two drams and forty-eight grains of that Salt, as it

is used in manufacturing Soap; that is, containing water enough to make

it crystallize; one ounce three drams twenty grains of Olive Oil; and

about two drams four grains of water.

As Acids have a greater affinity than any other substance with Alkalis,

they may be very effectually employed to decompound Soap.

If you propose to decompound Soap by means thereof, you must first

dissolve it in a sufficient quantity of water. Mr. Geoffroy, who made

this experiment likewise, dissolved two ounces thereof in about three

gallons of warm water, and to the solution added Oil of Vitriol, which

he let fall into it drop by drop. Every time a drop of Acid falls into

it, a _coagulum_ is formed in the liquor. The vessel in which the

solution is contained must then be shaken, that the Acid may equally

attack all the Alkali diffused in it. When no new coagulation is

produced by a drop of the Acid, it is a sign you have added enough.

The liquor then begins to grow clear: and if another quart of water be

added, in order to facilitate the separation of the oily particles, you

will see them rise and unite together on the surface of the liquor.

This is a pure, clear, true Olive Oil, hath its taste, its smell, and,

like it, is fluid in warm weather, and becomes fixed by cold. Yet it

differs in some respects from that which never hath been united with

an Alkali in order to form a Soap; for it burns more vividly and more

rapidly, and is soluble in Spirit of Wine. We shall account for these

differences when we come to treat of Ardent Spirits.

Not only the Vitriolic Acid, but all others, even those obtained from

vegetables, are capable of decompounding Soap, and separating the Oil

from the Alkali. In the liquor wherein Soap is thus decompounded is

found a Neutral Salt, consisting of the Acid made use of, united with

the Alkali of the Soap. If the Vitriolic Acid be used, you will have a

Glauber's Salt; a quadrangular Nitre, if the Nitrous Acid be used; and

so of the rest.

The facility with which Acids decompound Soap is the reason that no

water, but what is very pure, will dissolve it, or is fit to be used in

washing with it.

Water that doth not dissolve Soap well is usually called _Hard Water_.

Such waters contain a certain quantity of saline matters, washed out of

the earths through which they pass. The hardness of water is generally

occasioned by selenitic particles.

The hardness of all the well-water in and about Paris is owing to a

considerable quantity of Selenetic Gypsum with which the Soil abounds.

The Selenites, we know, are Neutral Salts, consisting of the Vitriolic

Acid united with an earthy basis. If therefore Soap be put into water

in which a Salt of this kind is dissolved, it is evident that the

Vitriolic Acid in the Selenites, having a greater affinity with the

fixed Alkali of the Soap than with its own earthy basis, will quit the

latter to unite with the former; and thus the Soap will be decompounded

instead of being dissolved. Accordingly we see, that, when we attempt

to dissolve Soap in our well-water, the surface of the liquor is

in a short time covered with a fat oily pellicle. However, this

decomposition of Soap is not complete; at least, but a small part of

it is perfectly decompounded; because the great quantity of Selenites,

with which the water is impregnated, hinders the Soap from mixing so

thoroughly with it, as is requisite to produce a total decomposition

thereof.