precipitation of the Silver, may in like manner be precipitated by
Iron, and, as it retains a small portion of Silver, ought not to
be neglected when these operations are performed on considerable
quantities.
In the two next processes we shall shew two other methods of separating
Silver from _aqua fortis_.
PROCESS V.
_To separate Silver from the Nitrous Acid by Distillation. Crystals of
Silver. The Infernal Stone._
Into a large, low, glass body put the solution of Silver, from which
you intend to separate the Silver by distillation. To this body fit
a tubulated head provided with its stopple. Set this alembic in a
sand-bath, so that the body may be almost covered with sand: apply
a receiver, and distil with a moderate heat, so that the drops may
succeed each other at the distance of some seconds. If the receiver
grow very hot, check the fire. When red vapours begin to appear, pour
into the alembic, through the hole in its head, a fresh quantity of
your solution of Silver, first made very hot. Continue distilling in
this manner, and repeating the addition of fresh liquor, till all your
solution be put into the alembic. When you have no more fresh solution
to put in, and when, the phlegm being all come over, red vapours begin
again to appear, convey into the alembic half a dram or a dram of
tallow, and distil to dryness; which being done, increase your fire so
as to make the vessel containing the sand-bath red-hot. In the alembic
you will find a calx of Silver, which must be melted in a crucible with
some soap and calcined wine-lees.
_OBSERVATIONS._
A low cucurbit is recommended for this operation, to the intent that
the particles of the Nitrous Acid, which are ponderous, may the more
easily be carried up and pass over into the receiver. For the same
reason the cucurbit is directed to be almost wholly covered with sand,
lest otherwise the acid vapours should be condensed about that part of
the cucurbit, which, being out of the sand, would be much cooler than
that which is encompassed therewith, and from thence should fall back
again to the bottom; by which means the distillation would certainly be
retarded, and the vessel probably be broken.
Notwithstanding these precautions the vessels are liable to break
in such distillations; especially when they contain a great deal of
liquor. With a view, therefore, to prevent this accident, we ordered
that the whole quantity of the solution of Silver to be distilled
should not be put at once into the alembic. The little bit of tallow,
added towards the end of the operation, is intended to hinder the metal
from adhering closely to the vessel, as it would otherwise do, when all
the moisture is dissipated.
The Soap and Fixed Alkali mixed with the Silver to flux it, after its
separation from the _aqua fortis_ in this way, serve to absorb such of
the most fixed particles of the Acid as may still remain united with
the metal.
If the distillation be stopped when part of the phlegm is drawn off,
and the liquor be then suffered to cool, many crystals will shoot
therein, which are a Neutral Salt constituted of the Nitrous Acid and
Silver. If the distillation be carried further, and stopped when near
its conclusion, the liquor being then suffered to cool will wholly
coagulate into a blackish mass called the _Infernal Stone_.
This way of separating Silver from its solvent is attended with the
advantage of saving all the _aqua fortis_, which is excellent, and fit
to be employed in other operations.
PROCESS VI.
_To separate Silver from the Nitrous Acid by Precipitation._ Luna
Cornea. Luna Cornea _reduced_.
Into your solution of Silver pour about a fourth part in weight of
Spirit of Salt, solution of Sea-salt, or solution of Sal Ammoniac. The
liquor will instantly become turbid and milky. Add twice or thrice
its weight of fair water, and let it stand some hours to settle. It
will deposite a white powder. Decant the clear liquor, and on the
precipitate pour fresh _aqua fortis_, or Spirit of Salt, and warm
the whole on a sand-bath with a gentle heat for some time. Pour off
this second liquor, and boil your precipitate in pure water, shifting
it several times, till the precipitate and the water be both quite
insipid. Filter the whole, and dry the precipitate, which will be a
_Luna Cornea_, and must be reduced in the following manner.
Smear the inside of a good crucible well with soap. Put your _Luna
Cornea_ into it; cover it with half its weight of Salt of Tartar,
thoroughly dried and pulverized; press the whole hard down; pour
thereon as much oil, or melted tallow, as the powder is capable of
imbibing; set the crucible thus charged, and close covered, in a
melting furnace, and, for the first quarter of an hour, make no more
fire than is necessary to make the crucible moderately red: after that
raise it so as to melt the Silver and the Salt, throwing into the
crucible from time to time little bits of tallow. When it ceases to
smoke, let the whole cool; or pour it into a hollow iron cone, warmed
and tallowed.
_OBSERVATIONS._
The process here delivered furnishes us with the means of procuring
Silver in a degree of purity which is not to be obtained by any other
method of treating it whatever. That which is refined on the cupel
always retains a small portion of Copper, from which it cannot possibly
be separated in that way: but if it be dissolved in _aqua fortis_,
and precipitated thence in a _Luna Cornea_ by the Marine Acid, the
precipitate will be an absolutely pure Silver, unalloyed with that
small portion of Copper which is retained on the cupel. The reason of
this effect is, that the Copper remains as perfectly dissolved in
Spirit of Salt and in _aqua regia_ as in _aqua fortis_: so that when
the Silver, and the Copper with which it is alloyed, are dissolved
together in the Nitrous Acid, if the Acid of Sea-salt be mixed with
the solution, part of this latter Acid unites with the Silver, and
therewith forms a new compound, which not being soluble in the liquor,
falls to the bottom. The other part of the Acid mixing with the
Nitrous, forms an _aqua regis_, in which the Copper remains dissolved,
without separating from it.
Fresh Acid is poured on the precipitated calx of Silver, in order to
complete the solution of the small portion of Copper that may have
escaped the action of the first solvent. It is indifferent whether
the Spirit of Salt or the Spirit of Nitre be employed for this
purpose, because they both dissolve Copper alike, and because Silver
precipitated by Spirit of Salt is not soluble in either.
After this it is necessary to wash the precipitate well with pure
water, in order to free it entirely from the particles of _aqua fortis_
adhering to the Silver; because they may possibly contain something
of Copper, which would mix with the Silver in melting, and taint its
purity.
If this precipitate of Silver be exposed to the fire, unmixed with any
other substance, it melts as soon as it begins to be red; and, if the
fire be increased, part thereof will be dissipated in vapours, and the
rest will make its way through the crucible. But being poured out as
soon as melted, it coagulates into a cake of a purplish red colour,
semi-transparent, ponderous, and in some degree pliable, especially
if it be very thin. It bears some resemblance to horn, which hath
occasioned it to be called _Luna Cornea_.
As _Luna Cornea_ is not soluble in water, recourse must be had to
fusion, in order to reduce it, by separating from the Silver those
acids which give it the above-mentioned properties. Fixed Alkalis and
fatty matters are very fit to produce that separation.
We directed that the inside of the crucible, in which the reduction is
to be made, should be carefully smeared with soap, and that the _Luna
Cornea_ should be quite covered with a Fixed Alkali and fat, to the end
that when the heat is strong enough to dissipate it in vapours, or to
attenuate it so as to render it capable of penetrating the crucible, it
may be forced to pass through matters qualified to absorb its Acid, and
reduce it.
_Luna Cornea_ may also be reduced by being melted with such metalline
substances as have a greater affinity than Silver with the Acids
wherewith it is impregnated. Of this kind are Tin, Lead, Regulus of
Antimony: but the _Luna Cornea_ rushes so impetuously into conjunction
with those metalline substances, that a vast many vapours arise, and
carry off with them part of the Silver: if therefore you chuse to
effect the reduction by the interposition of such metalline substances,
you must employ a retort instead of a crucible.
But this method is attended with another inconvenience; which is, that
some part of those metalline substances may unite with the Silver, and
adulterate it: for which reason it is best to keep to the method first
proposed.
PROCESS VII.
_To dissolve Silver, and separate it from Gold, by Cementation._
Mix thoroughly together fine brick-dust four parts, Vitriol calcined to
redness one part, and Sea-salt or Nitre one part. Moisten this powder
with a little water. With this cement cover the bottom of a crucible
half an inch thick; on this first bed lay a thin plate of the mass of
Gold and Silver you intend to cement, and which you must previously
take care to beat into such thin plates. Cover this plate with a second
layer of cement, of the same thickness as the former; on this second
bed lay another plate of your metal; cover it in like manner with
cement; and so proceed till the crucible be filled to within half an
inch of its brim. Fill up the remaining space with cement, and close
the crucible with a cover, luted with a paste made of Windsor-loam and
water: set your crucible thus charged in a furnace, whose fire-place
is deep enough to let it be entirely surrounded with coals, quite up to
its mouth. Light some coals in the furnace, taking care not to make the
fire very brisk at first; increase it by degrees, but only so far as to
make the crucible moderately red; keep up the fire in this degree for
eighteen or twenty hours: then let the fire go out; open the crucible
when it is cold, and separate the cement from your plates of Gold.
Boil the Gold repeatedly in fair water, till the water come off quite
insipid.
_OBSERVATIONS._
It cannot but seem strange, that, after having so often declared the
Acid of Sea-salt to be incapable of dissolving Silver, we should
direct either Nitre or Sea-salt indifferently to be employed in
composing a cement, which is to produce an Acid capable of eating
out all the Silver mixed with Gold. It is easy to conceive how the
Nitrous Acid extricated from its basis by means of the Vitriolic Acid
may produce this effect: but if Sea-salt instead of Nitre be made an
ingredient in the cement, its Acid, though set at liberty in the same
manner by the Vitriolic Acid, must at first sight appear unable to
answer the end.
In order to remove this difficulty, we must here observe, that there
are two very essential differences between the Marine Acid collected
in a liquor, as it is when distilled in the usual manner, and the same
Acid separated from its basis in a crucible, as it is in cementation.
The first of these two differences is, that the Acid being reduced
into vapours when it acts on the Silver in cementation, its activity
is thereby greatly increased: the second is, that in the crucible it
sustains a vastly greater degree of heat than it can ever bear when
it is in the form of a liquor. For, after it is once distilled and
separated from its basis, it cannot sustain any extraordinary degree
of heat without being volatilized and entirely dissipated: whereas,
while it continues united with its basis, it is much more fixed, and
cannot be separated but by a very intense heat. Consequently, if it
meet with any body to dissolve, at the very instant of its separation
from its basis, while it is actuated by a much fiercer heat than can
ever be applied to it on any other occasion, it must operate upon that
body with so much the more efficacy: and thus it comes to pass, that in
cementation it has the power of dissolving Silver, which it would be
incapable of touching if it were not so circumstanced.
But herein Gold differs from Silver: for, whatever force the Nitrous
or the Marine Acid may exert, when extricated from their bases in the
cementing crucible, this metal obstinately refuses to yield to either
of those Acids separately, and can never be dissolved by them, unless
both be united together.
Our cementation, therefore, is actually a parting process in the dry
way. The Silver is dissolved, and the Gold remains unaltered. Nay, as
the action of the Acids is much stronger when they are applied this
way, than when they are used for dissolution in the moist way, the
Nitrous Acid, which in the common parting process will not dissolve
Silver unless its weight be double that of the Gold, is able in
cementation to dissolve a very small quantity of Silver diffused
through a large quantity of Gold.
It sometimes happens, that after the operation the cement proves
extremely hard, so that it is very troublesome to separate it entirely
from the Gold. In this case it must be softened by moistening it with
hot water. This hardness which the cement acquires is occasioned by
the fusion of the Salts, which is the effect of too strong a heat. It
was in order to prevent this, and that a due degree of heat might be
applied, without the danger of melting the salts, that we directed
the cement to be mixed with a considerable quantity of earthy matter
incapable of fusion, such as brick-dust. A greater inconvenience will
ensue, if the fire be made so strong as to melt the Gold: for then it
will partly commix again with the other metalline substances dissolved
by the cement, and consequently will not be purified.
The crucible is covered, and its cover luted on, to prevent the acid
vapours from being too soon dissipated, and to force them to circulate
the longer in the crucible. However, it is necessary that those vapours
should find a vent at last, otherwise they would burst the vessel:
and for this reason we directed the crucible to be luted only with
Windsor-loam, which does not grow very hard by the action of fire, and
so is capable of yielding and giving passage to the vapours, when a
certain quantity of them is collected in the crucible, and they begin
to struggle for an escape on every side.
When the operation is finished, the Silver dissolved by the Acid of
the cement is partly distributed through the cement, and partly in the
Gold itself, which is impregnated therewith. For this reason the Gold
must be washed several times in boiling water, till the water become
absolutely insipid: for, if the Gold be melted without this precaution,
it will mix again with the Silver: the cement also may be washed in the
same manner to recover the Silver it contains.
Though this cementation be, properly speaking, a purification of
Gold, yet we have placed it among the processes on Silver, because it
is the Silver that is dissolved on this occasion, and because this
is a particular way of dissolving that metal. Moreover, most of the
processes hitherto delivered, either on Gold or Silver, are equally
applicable to both these metals.
If the Gold do not appear quite pure after the cementation, the process
must be repeated.
There are several ways to know the fineness of Gold, the quantity of
Silver with which it is alloyed, and the proportion in which these two
metals are mixed in a mass purified by the cupel.
One of the simplest is the trial by the Touch-stone; which indeed is
hardly any more than judging by the eye only, from the colour of the
compound metal, what proportion of Gold and Silver it contains.
The Touch-stone is a sort of black marble, whose surface ought to be
half polished. If the metalline mass which you want to try be rubbed
on this stone, it leaves thereon a thin coat of metal, the colour of
which may be easily observed. Such as are accustomed to see and handle
Gold and Silver can at once judge very nearly from this sample in what
proportion the two metals are combined: but, for greater accuracy,
those who are in the way of having frequent occasion for this trial
are provided with a sufficient number of small bars or needles, of
which one is pure Gold, another pure Silver, and all the rest consist
of these two metals mixed together in different proportions, varied
by carats, or even by fractions of carats, if greater exactness be
required.
The fineness of each needle being marked on it, that needle whose
colour seems to come nearest the colour of the metalline streak on the
Touch-stone, is rubbed on the stone by the side of that streak. This
needle likewise leaves a mark; and if there appear to be no difference
between the two metalline streaks, the metalline mass is judged to be
of the same fineness as the needle thus compared with it. If the eye
discovers a sensible difference, another needle is sought for whose
colour may come nearer to that of the metal to be tried. But though
a man be ever so well versed in judging thus of the fineness of Gold
by the eye only, he can never be perfectly and accurately sure of it
by this means alone. If such certainty be required, recourse must be
had to the parting assay; and yet when you have gone through it, there
always remains a small quantity of the metal, which should have been
dissolved, and yet escaped the action of the solvent. For example,
if you make use of _aqua regis_, the Silver that remains after the
operation still contains a little Gold; and, if you make use of _aqua
fortis_, the Gold that remains after the operation still contains a
little Silver. And therefore if you resolve to carry the separation
of these two metals still further by solvents, it will be necessary,
after you have gone through one parting process, to perform a second
the contrary way. For example, if you begin with _aqua fortis_, then,
after it has dissolved all the Silver in the metalline mass that it is
capable of taking up, dissolve the remaining Gold in _aqua regis_: by
which means you will separate the small portion of Silver left in it by
the _aqua fortis_. The contrary is to be done if you made use of _aqua
regis_ first.
CHAP. III.
_Of_ COPPER.
PROCESS I.
_To separate Copper from its Ore._
Beat your Copper ore to a fine powder, having first freed it as
accurately as possible, by washing and roasting, from all stony,
earthy, sulphureous, and arsenical parts. Mix your ore thus pulverized
with thrice its weight of the black flux; put the mixture into a
crucible; cover it with common salt to the thickness of half an inch,
and press the whole down with your finger. With all this the crucible
must be but half full. Set it in a melting furnace; kindle the fire by
degrees, and raise it insensibly till you hear the Sea-salt crackle.
When the decrepitation is over, make the crucible moderately red-hot
for half a quarter of an hour. Then give a considerable degree of heat,
exciting the fire with a pair of good perpetual bellows, so that the
crucible may become very red-hot, and be perfectly ignited. Keep the
fire up to this degree for about a quarter of an hour; then take out
the crucible, and with a hammer strike a few blows on the floor whereon
you set it. Break it when cold. If the operation hath been rightly and
successfully performed, you will find at the bottom of the vessel a
hard Regulus, of a bright yellow colour, and semi-malleable; and over
it a scoria of a yellowish brown colour, hard and shining, from which
you may separate the Regulus with a hammer.
_OBSERVATIONS._
Copper in the ore is often blended with several other metallic
substances, and with volatile minerals, such as Sulphur and Arsenic.
Copper ores also frequently participate of the nature of the pyrites,
containing a martial and an unmetallic earth, both of which are
entirely refractory, and hinder the ore from melting. In this case you
must add equal parts of a very fusile glass, a little borax, and four
parts of the black flux, to facilitate the fusion. The black flux is
moreover necessary to furnish the Copper with the Phlogiston it wants,
or restore so much thereof as it may lose in melting. For the same
reason, when any ore, but that of Gold or Silver, is to be smelted, it
is a general rule to add some black flux, or other matter abounding
with Phlogiston.
The Regulus produced by this operation is not malleable, because it is
not pure Copper, but a mixture of Copper with all the other metallic
substances that were in the ore; except such as were separated from it
by roasting, of which it contains but little.
According to the nature of the metallic matters that remain combined
with the Copper after this fusion, the colour of the Regulus is
either like that of pure Copper, or a little more whitish: it is also
frequently blackish, which has procured it the name of _Black Copper_.
In this state, and even in general, it is usual enough to call this
Regulus by the name of Black Copper, when alloyed with other metallic
substances that render it unmalleable, whatever its colour be.
Hence it appears that there may be several different sorts of Black
Copper. Iron, Lead, Tin, Bismuth, and the reguline part of Antimony,
are almost always combined with the ores of Copper, in a multitude of
different proportions; and all these substances, being reduced by the
black flux in the operation, mix and precipitate with the Copper. If
the ore contain any Gold or Silver, as is pretty often the case, these
two metals also are confounded with the rest in the precipitation, and
become part of the Black Copper.
Pyritose, sulphureous, and arsenical Copper ores may be fused, in order
to get rid of the grosser heterogeneous parts, without previously
roasting them: but in this case no alkaline flux must be mixed with the
ore; because the Alkali in combination with the Sulphur would produce
a Liver of Sulphur, and so dissolve the metalline part; by which means
all would be confounded together, and no Regulus, or very little, be
precipitated. On this occasion therefore nothing must be added to
promote the fusion, but some tender fusile glass, together with a small
quantity of borax.
This first fusion may also be performed amidst the coals, by casting
the ore upon them in the furnace, without using a crucible; and then an
earthen vessel, thoroughly heated, or even made red-hot, must be placed
under the grate of the fire-place, to receive the metal as it runs from
the ore.
The Regulus obtained by this means is much more impure and brittle
than Black Copper, because it contains moreover a large quantity of
Sulphur and Arsenic; as these volatile substances have not time to
evaporate during the short space requisite to melt the ore, and as they
cannot be carried off by the action of the fire after the ore is once
melted, whatever time be allowed for that purpose. However, some part
thereof is dissipated; and the Iron which is in pyritose ores, having a
much greater affinity than Copper, and indeed than any other metallic
substance, with Sulphur and Arsenic, absorbs another part thereof, and
separates it from the Regulus.
This Regulus, it is plain, still contains all the same parts that were
in the ore, but in different proportions; there being more Copper,
combined with less Sulphur, Arsenic, and unmetallic earth, which have
been either dissipated or turned to slag. Therefore, if you would make
it like Black Copper, you must pound it, roast it over and over, to
free it from its Sulphur and Arsenic, and then melt it with the black
flux.
If this Regulus contain much Iron, it will be adviseable to melt it
once or twice more, before all the Sulphur and Arsenic are separated
from it by roasting; for as the Iron, by uniting with these volatile
substances, separates them from the Copper, with which they have not so
great an affinity; so also the Sulphur and Arsenic, by uniting with the
Iron, help in their turn to separate it from the Copper.
PROCESS II.
_To purify Black Copper, and render it malleable._
Break into small bits the Black Copper you intend to purify; mix
therewith a third part in weight of granulated Lead, and put the
whole into a cupel set under the muffle in a cupelling furnace, and
previously heated quite red. As soon as the metals are in the cupel
raise the fire considerably, making use, if it be needful, of a pair of
perpetual bellows, to melt the Copper speedily. When it is thoroughly
melted, lower the fire a little, and continue it just high enough to
keep the metalline mass in perfect fusion. The melted matter will then
boil, and throw up some _scoriæ_, which will be absorbed by the cupel.
When most of the Lead is consumed, raise the fire again, till the face
of the Copper become bright and shining, thereby shewing that all its
alloy is separated. As soon as your Copper comes to this state, cover
it with charcoal-dust conveyed into the cupel with an iron ladle: then
take the cupel out of the furnace and let it cool.
_OBSERVATIONS._
Of all the metals, next to Gold and Silver, Copper bears fusion the
longest without losing its phlogiston; and on this property is founded
the process here delivered for purifying it.
It is necessary the Copper should melt as soon as it is in the cupel,
because its nature is to calcine much more easily and much sooner,
when it is only red-hot, than when it is in fusion. For this reason
the fire is to be considerably raised, immediately on putting the
Copper under the muffle, that it may melt as soon as possible. Yet too
violent a degree of fire must not be applied to it: for when it is
exposed to such a degree of heat only as is but just necessary to keep
it in fusion, it is then in the most favourable condition for losing
as little as may be of its phlogiston; and if the heat be stronger,
a greater quantity thereof will be calcined. As soon therefore as it
flows it is proper to weaken the fire, and reduce it to the degree just
requisite to keep up the fusion.
The Lead added on this occasion is intended to facilitate and expedite
the scorification of the metallic substances combined with the Copper.
So that the event is here nearly the same as when Gold or Silver is
refined on the cupel. The only difference between this refining of
Copper, and that of the perfect metals, is that the latter as hath been
shewn, absolutely resist the force of fire and the action of Lead,
without suffering the least alteration; whereas a good deal of Copper
is calcined and destroyed, when it is purified in this manner on the
cupel. Indeed it would be wholly destroyed, if a greater quantity of
Lead were added, or if it were left too long in the furnace. It is with
a view to save as much of it as possible that we order it to be covered
with charcoal-dust as soon as the scorification is finished.
The Lead serves moreover to free the Copper expeditiously from the
Iron with which it may be alloyed. Iron and Lead are incapable of
contracting any union together: so that as fast as the Lead unites with
the Copper, it separates the Iron, and excludes it out of the mixture.
For the same reason if Iron were combined in a large proportion with
Copper, it would prevent the Lead from entering into the composition.
Now, as it is necessary to give the more heat, and to keep the Copper
to be incorporated with Lead the longer in fusion, as that Copper is
alloyed with a greater proportion of Iron, some black flux must be
added on this occasion, to prevent the Copper and the Lead from being
calcined before their association can be effected.
Copper purified in the manner here directed is beautiful and malleable.
It is now alloyed with no other metalline substance but Gold or Silver,
if there were any in the mixed mass. If you desire to extract this Gold
or Silver, recourse must be had to the operation of the cupel. The
process here given for purifying Copper is not used in large works,
because it would be much too chargeable. In order to purify their Black
Copper, and render it malleable, the smelters content themselves with
roasting it, and melting it repeatedly, that the metallic substances,
which are not so fixed as Copper, may be dissipated by sublimation, and
the rest scorified by fusion.
PROCESS III.
_To deprive Copper of its Phlogiston by calcination._
Put your Copper in filings into a test, and set it under the muffle of
a cupelling furnace; light the fire, and keep up such a degree of heat
as may make the whole quite red, but not enough to melt the Copper.
The surface of the Copper will gradually lose its metalline splendour,
and put on the appearance of a reddish earth. From time to time stir
the filings with a little rod of copper or iron, and leave your metal
exposed to the same degree of fire till it be entirely calcined.
_OBSERVATIONS._
In our observations on the preceding process we took notice that
Copper, in fusion, calcines more slowly, and less easily, than when it
is exposed to a degree of fire barely sufficient to keep it red-hot,
without melting it; and therefore, the design here being to calcine it,
we have directed that degree of heat only to be applied.
The cupelling furnace is the fittest for this operation, because the
muffle is capable of receiving such a flat vessel as ought to be used
on this occasion, and communicating to it a great deal of heat; while,
at the same time, it prevents the falling in of any coals, which, by
furnishing the Copper with fresh phlogiston, would greatly prejudice
and protract the operation.
As Copper calcines with great difficulty, this operation is extremely
tedious: nay, though Copper hath stood thus exposed to the fire
for several days and nights, and seems perfectly calcined, yet it
frequently happens that, when you try afterwards to melt it, some of
it resumes the form of Copper: a proof that all the Copper had not
lost its phlogiston. Copper is much more expeditiously deprived of its
phlogiston by calcining it in a crucible with Nitre.
The calx of Copper perfectly calcined is with great difficulty brought
to fusion: yet, in the focus of a large burning-glass, it melts and
turns to a reddish and almost opaque glass.
By the process here delivered, you may likewise calcine all other
metalline substances, which do not melt till they are thoroughly
red-hot. As to those which melt before they grow red, they are easily
enough calcined, even while they are in fusion.
PROCESS IV.
_To resuscitate the Calx of Copper, and reduce it to Copper, by
restoring its Phlogiston._
Mix the Calx of Copper with thrice as much of the black flux; put the
mixture into a good crucible, so as to fill two thirds thereof, and
over it put a layer of Sea-salt a finger thick. Cover the crucible, and
set it in a melting furnace; heat it gradually, and keep it moderately
red till the decrepitation of the Sea-salt be over. Then raise the fire
considerably by means of a good pair of perpetual bellows; satisfy
yourself that the matter is in perfect fusion, by dipping into the
crucible an iron wire; continue the fire in this degree for half a
quarter of an hour. When the crucible is cold, you will find at its
bottom a button of very fine Copper, which will easily separate from
the saline scoria at top.
_OBSERVATIONS._
What hath been said before on the smelting of Copper ores may be
applied to this process, as being the very same. The observations there
added should therefore be consulted on this occasion.
PROCESS V.
_To dissolve Copper in the Mineral Acids._
On a sand-bath, in a very gentle heat, set a matrass containing some
Copper filings; pour on them twice their weight of Oil of Vitriol. That
Acid will presently attack the Copper. Vapours will rise, and issue
out of the neck of the matrass. A vast number of bubbles will ascend
from the surface of the metal to the top of the liquor, and the liquor
will acquire a beautiful blue colour. When the Copper is dissolved, put
in a little and a little more, till you perceive the Acid no longer
acts upon it. Then decant the liquor, and let it stand quiet in a cool
place. In a short time great numbers of beautiful blue crystals will
shoot in it. These crystals are called _Vitriol of Copper_, or _Blue
Vitriol_. They dissolve easily in water.
_OBSERVATIONS._
The Vitriolic Acid perfectly dissolves Copper, which is also soluble in
all the Acids, and even in many other menstruums.
This Acid may be separated from the Copper which it hath dissolved by
distillation only: but the operation requires a fire of the utmost
violence. The Copper remaining after it must be fused with the black
flux, to make it appear in its natural form; not only because it still
retains a portion of the Acid, but also because it hath lost part of
its phlogiston by being dissolved therein. The black flux is very well
adapted both to absorb the Acid that remains united with the Copper,
and to restore the phlogiston which the metal hath lost.
The most usual method of separating Copper from the Vitriolic Acid
is by presenting to that Acid a metal with which it hath a greater
affinity than with Copper. Iron being so qualified is consequently very
fit to bring about this separation. When therefore plates of Iron well
cleaned are laid in a solution of Blue Vitriol, the Acid soon begins to
act upon them, and by degrees, as it dissolves them, deposites on their
surfaces a quantity of Copper in proportion to the quantity of Iron it
takes up. The Copper thus precipitated hath the appearance of small
leaves or scales, exceeding thin, and of a beautiful copper-colour.
Care must be taken to shake the Iron-plates now and then, to make the
scales of Copper fall off, which will otherwise cover them entirely,
hinder the Vitriolic Acid from attacking the Iron, and so put a stop to
the precipitation of the remaining Copper.
When these scales of Copper cease to settle on the clean Iron
plates, you may be sure all the Copper that was in the liquor is
precipitated, and that this liquor, which was a solution of Copper
before the precipitation, is a solution of Iron after it. So that here
two operations are performed at one and the same time; to wit, the
precipitation of the Copper, and the dissolution of the Iron.
The Copper thus precipitated requires only to be separated from the
liquor by filtration, and melted with a little black flux, to become
very fine malleable Copper.
The Copper may also be precipitated out of a solution of Blue Vitriol
by the interposition of a Fixed Alkali. This precipitate is of a
greenish blue colour, and requires a much greater quantity of the black
flux to reduce it.
Copper dissolves in the Nitrous Acid, in the Marine Acid, and in _Aqua
regis_; from all of which it may be separated by the same methods as
are here ordered with regard to the Vitriolic Acid.
CHAP. IV.
_Of_ IRON.
PROCESS I.
_To separate Iron from its Ore._
Pound into a coarse powder the martial stones or earths out of which
you design to extract the Iron: roast this powder in a test under the
muffle for some minutes, and let your fire be brisk. Then let it cool,
beat it very fine, and roast it a second time, keeping it under the
muffle till it emit no more smell.
Then mix with this powder a flux composed of three parts of Nitre fixed
with Tartar, one part of fusile glass, and half a part of Borax and
charcoal-dust. The dose of this reducing flux must be thrice the weight
of the ore.
Put this mixture into a good crucible; cover it with about half a
finger thick of Sea-salt; over the crucible put its cover, and lute it
on with Windsor-loam made into a paste with water. Having thus prepared
your crucible, set it in a melting furnace, which you must fill up with
charcoal. Light the fire, and let it kindle by gentle degrees, till
the crucible become red-hot. When the decrepitation of the Sea-salt
is over, raise your fire to the highest by the blast of a pair of
perpetual bellows, or rather several. Keep up this intense degree of
heat for three quarters of an hour, or an whole hour, taking care that
during all this time the furnace be kept constantly filling up with
fresh coals as the former consume. Then take your crucible out of the
furnace; strike the pavement on which you set it several times with a
hammer, and let it stand to cool: break it, and you will find therein a
Regulus of Iron covered with slag.
_OBSERVATIONS._
Iron ore, like all others, requires roasting, to separate from it, as
much as possible, the volatile minerals, Sulphur and Arsenic, which
being mixed with the Iron would render it unmalleable. Indeed it is
so much the more necessary to roast these ores, as Iron is, of all
metallic substances, that which has the greatest affinity with those
volatile minerals; on which account no metallic substance whatever is
capable of separating it from them by fusion and precipitation.
Fixed Alkalis, it is true, have a greater affinity than Iron with
Sulphur; but then the composition which a Fixed Alkali forms with
Sulphur is capable of dissolving all metals. Consequently, if you do
not dissipate the Sulphur by roasting, but attempt to separate it from
the Iron by melting the ore with a Fixed Alkali, the Liver of Sulphur
formed in the operation will dissolve the martial part; so that after
the fusion you will find little or no Regulus.
All Iron ores in general are refractory, and less fusible than any
other; for which reason a much greater proportion of flux, and a much
more violent degree of fire, is required to smelt them. One principal
cause why these ores are so refractory is the property which Iron
itself has of being extremely difficult to fuse, and of resisting
the action of the fire so much the more as it is purer, and further
removed from its mineral state. Among all the metallic substances it is
the only one that is less fusible when combined with that portion of
phlogiston which gives it the metalline form, than when it is deprived
thereof, and in the form of a calx.
In smelting-houses Iron ore is fused amidst charcoal, the phlogiston
of which combines with the martial earth, and gives it the metalline
form. The Iron thus melted runs down to the bottom of the furnace, from
whence it is let out into large moulds, in which it takes the shape of
oblong blocks, called _Pigs_ of Iron. This Iron is still very impure,
and quite unmalleable. Its want of ductility after the first melting
arises partly from hence, that, notwithstanding the previous roasting
which the ore underwent, there still remains, after this first fusion,
a considerable quantity of Sulphur or Arsenic combined with the metal.
A certain quantity of quick-lime, or of stones that will burn to lime,
is frequently mixed with Iron ore on putting it into the smelting
furnace. The lime being an absorbent earth, very apt to unite with
Sulphur and Arsenic, is of use to separate those minerals from the Iron.
It is also of use to mix some such matters with the ore, when the
stones or earths which naturally accompany it are very fusible; for, as
the Iron is of difficult fusion, it may happen that the earthy matters
mixed with the Iron shall melt as easily as the metal, or perhaps
more easily. In such a case there is no separation of the earthy
from the metalline part, both of which melt and precipitate together
promiscuously; now quick-lime, being extremely refractory, serves on
this occasion to check the melting of those matters which are too
fusible.
Yet quick-lime, notwithstanding its refractory quality, may sometimes
be of use as a flux for Iron. This is the case when the ore happens to
be combined with substances which, being united with lime, render it
fusible: such are all arsenical matters, and even some earthy matters,
which being combined with quick-lime make a fusible compound.
When the ore of an Iron mine is found difficult to reduce, it is
usually neglected even though it be rich: because Iron being very
common, people chuse to work those mines only whose ores are smelted
with the most ease, and require the least consumption of wood.
Yet refractory ores are not to be altogether rejected, when another
Iron ore of a different quality is found near them. For it often
happens, that two several Iron ores, which being worked separately
are very difficult to manage, and yield at last but bad metal, become
very tractable, and yield excellent Iron, when smelted together: and
accordingly such mixtures are often made at Iron-works.
The Iron obtained from ores by the first fusion may be divided into two
sorts. The one, when cold, resists the hammer, doth not easily break,
and is in some measure extensible on the anvil; but, if struck with a
hammer when red-hot, flies into many pieces: this sort of Iron hath
always a mixture of Sulphur in it. The other sort, on the contrary, is
brittle when cold, but somewhat ductile when red-hot. This Iron is not
sulphurated, is naturally of a good quality, and its brittleness arises
from its metalline parts not being sufficiently compacted together.
Iron abounds so much, and is so universally diffused through the earth,
that it is difficult to find a body in which there is none at all: and
this hath led several Chymists, even men of great fame, into the error
of thinking that they had transmuted into Iron several sorts of earths
in which they suspected no Iron, by combining them with an inflammable
matter; whereas, in fact, all they did was to give the metalline form
to a true martial earth which happened to be mixed with other earths.
PROCESS II.
_To render Pig-iron and brittle Iron malleable._
Into an earthen vessel widening upwards put some charcoal-dust, and
thereon lay the Pig-iron which you propose to render ductile; cover it
all over with a quantity of charcoal; excite the fire violently with a
pair, or more, of perpetual bellows till the Iron melt. If it do not
readily flow and form a great deal of slag on its surface, add some
flux, such as a very fusible sand.
When the matter is in fusion keep stirring it from time to time, that
all the parts thereof may be equally acted on by the air and the fire.
On the surface of the melted Iron _scoriæ_ will be formed, which must
be taken off as they appear. At the same time you will see a great many
sparkles darted up from the surface of the metal, which will form a
sort of fiery shower. By degrees, as the Iron grows purer, the number
of these sparkles diminishes, though they never vanish entirely. When
but few sparkles appear, remove the coals which cover the Iron, and
let the slag run out of the vessel; whereupon the metal will grow
solid in a moment. Take it out while it is still red-hot, and give
it a few strokes with a hammer, to try if it be ductile. If it be
not yet malleable, repeat the operation a second time, in the same
manner as before. Lastly, when it is thus sufficiently purified by the
fire, work it for a long time on the anvil, extending it different
ways, and making it red-hot as often as there is occasion. Iron thus
brought to the necessary degree of ductility, so as to yield to the
hammer, and suffer itself to be extended every way, either hot or cold,
without breaking to bits, or even cracking in the least, is very good
and very pure. If it cannot be brought to this degree by the method
here prescribed, it is a proof that the ore from which this Iron was
extracted ought to be mixed with other ores; but it frequently requires
a great number of trials to obtain an exact knowledge of the quality
and proportion of those other ores with which it is to be mixed.
_OBSERVATIONS._
The brittleness and shortness of Pig-iron arises from the heterogeneous
parts which it contains, and which could not be separated from it
by the first fusion. These extraneous matters are usually Sulphur,
Arsenic, and unmetallic earth, and also a ferruginous earth; but
such as could not be combined with the phlogiston as it ought to be,
in order to have the properties of a metal, and must therefore be
considered as heterogeneous, with respect to the other well-conditioned
martial particles.
The Pig-iron, by undergoing repeated fusions, is freed from those
heterogeneous matters; those which are volatile, such as Sulphur and
Arsenic, being dissipated, and the unmetallic matters being scorified.
As to the ferruginous earth, which did not at first acquire the
metalline form, it becomes true Iron at last; because, among the coals
with which it is encompassed, it meets with a sufficient quantity of
phlogiston to reduce it to metal. Charcoal is also necessary on this
occasion, that it may continually furnish phlogiston to the Iron, which
would otherways be converted into a calx.
Hammering the red-hot Iron, after each fusion, serves to force out from
amongst the martial parts such earthy matters as may happen to remain
there, and so bring into closer contact the metalline parts which were
separated before by the interposition of those heterogeneous matters.
PROCESS III.
_To convert Iron into Steel._
Take small bars of the best Iron; that is, of such as is malleable both
hot and cold; set them on their ends in a cylindrical earthen vessel,
whose depth is equal to the length of the bars, and in such a manner
that they may be an inch distant from each other, and from the sides of
the crucible. Fill the vessel with a cement compounded of two parts of
charcoal, one part of bones burnt in a close vessel till they become
very black, and one half part of the ashes of green wood; having first
pulverized and thoroughly mixed the whole together. Take care to lift
up the Iron bars a little, to the end that the cement may cover the
bottom of the vessel, and so that there be about the depth of half an
inch thereof under every bar: cover the crucible and lute on the cover.
Set the crucible thus prepared in a furnace, so contrived that the
crucible may be surrounded with coals from top to bottom: for eight
or ten hours keep up such a degree of fire that the vessel may be
moderately red; after this take it out of the furnace; plunge your
little Iron bars into cold water, and you will find them converted into
Steel.
_OBSERVATIONS._
The principal difference between Iron and Steel consists in this, that
the latter is combined with a greater quantity of phlogiston than the
former.
It appears by this experiment, that, to make Iron unite with an
inflammable matter, it is not necessary it should be in fusion; it is
sufficient that it be so red-hot as to be opened and softened by the
fire.
Every kind of charcoal is fit to be an ingredient in the composition
of the cement employed to make Steel, provided it contain no Vitriolic
Acid. However, it hath been observed, that animal coals produce a
speedier effect than others: for which reason it is proper to mix
something of that kind with charcoal-dust, as above directed.
The following signs shew that the operation hath succeeded, and that
the Iron is changed into good Steel.
This metal being quenched in cold water, as proposed above, acquires
such an extraordinary degree of hardness, that it will by no means
yield to any impression of the file or hammer, and will sooner break
in pieces than stretch upon the anvil. And here it is proper to
observe, that the hardness of Steel varies with the manner in which it
is quenched. The general rule is, that the hotter the Steel is when
quenched, and the colder the water is in which you quench it, the
harder it becomes. It may be deprived of the temper thus acquired,
by making it red-hot, and letting it cool slowly; for it is thereby
softened, rendered malleable, and the file will bite upon it. For this
reason the artisans who work in Steel begin with untempering it, that
they may with more ease shape it into the tool they intend to make.
They afterwards new-temper the tool when finished, and by this second
temper the Steel recovers the same degree of hardness it had acquired
by the first temper.
The colour of Steel is not so white as that of Iron, but darker, and
the grains, facets, or fibres, which appear on breaking it, are finer
than those observed in Iron.
If the bars of Iron thus cemented in order to convert them into Steel
be too thick, or not kept long enough in cementation, they will not be
turned into Steel throughout their whole thickness: their surfaces only
will be Steel to a certain depth, and the center will be mere Iron;
because the phlogiston will not have thoroughly penetrated them. On
breaking a bar of this sort, the difference in colour and grain between
the Steel and the Iron is very visible.
It is easy to deprive Steel of the super-abundant quantity of phlogiston
which constitutes it Steel, and thereby reduce it to Iron. For this
purpose it need only be kept red-hot some time, observing that no
matter approach it all the while that is capable of refunding to it
the phlogiston which the fire carries off. The same end is still
sooner obtained by cementing it with meagre hungry matters, capable
of absorbing the phlogiston; such as bones calcined to whiteness, and
cretaceous earths.
Steel may also be made by fusion; or Pig-iron may be converted into
Steel. For this purpose the same method must be employed as was
above directed for reducing Pig-iron into malleable Iron; with this
difference, that, as Steel requires more phlogiston than is necessary
to Iron, all the means must be made use of that are capable of
introducing into the Iron a great deal of phlogiston; such as melting
but a small quantity of Iron at a time, and keeping it constantly
encompassed with abundance of charcoal; reiterating the fusions; taking
care that the blast of the bellows directed along the surface of the
metal do not remove the coals that cover it, _&c._ And here it must
be observed, that there are some sorts of Pig-iron which it is very
difficult to convert into Steel by this method, and that there are
others which succeed very readily, and with scarce any trouble at all.
The ores which yield the last-mentioned sort of Pig-iron are called
_Steel Ores_. Steel made by this means must be tempered in the same
manner as that made by cementation[8].
[8] M. Réaumur hath obliged the public with a treatise on the means
of converting Iron into Steel, in which he hath exhausted the subject.
Such as desire the amplest and most useful instructions on that part
of metallurgy, would do well to consult his Work.
PROCESS IV.
_The Calcination of Iron. Sundry Saffrons of Mars._
Take filings of Iron, in what quantity you please; put them into a
broad unglazed earthen vessel; set it under the muffle of a cupelling
furnace; make it red-hot; stir the filings frequently; and keep up the
same degree of fire till the Iron be wholly turned into a red powder.
_OBSERVATIONS._
Iron easily loses its phlogiston by the action of fire. The calx
that remains after its calcination is exceeding red; which makes
this be thought the natural colour of the earth of that metal. It
hath accordingly been observed, that all the earths and stones which
either are naturally red, or acquire that colour by calcination, are
ferruginous.
The yellowish red colour which every calx of Iron hath, in whatever
manner it be prepared, hath procured the name of _Crocus_ or _Saffron_
to every preparation of this kind. That made in the manner above
directed is called in Medicine _Crocus Martis astringens_.
The rust produced on the surface of Iron is a sort of calx of Iron made
by way of dissolution. The moisture of the air acts upon the metal,
dissolves it, and robs it of some of its phlogiston. This rust is
called in Medicine _Crocus Martis Aperiens_; because it is thought that
the saline parts, by means whereof the humidity dissolves the Iron,
remain united with the metal after its dissolution, and give it an
aperitive virtue. The Apothecaries prepare this sort of Saffron of Mars
by exposing Iron filings to the dew, till they be turned entirely to
rust: which is then called _Saffron of Mars by dew_.
Another Saffron of Mars is also prepared in a much shorter manner, by
mixing filings of Iron with pulverized Sulphur, and moistening the
mixture, which after some time ferments and grows hot. It is then set
on the fire; the Sulphur burns away, and the mass is kept stirring till
it become a red matter. This Saffron is nothing but Iron dissolved by
the Acid of Sulphur, which is known to be of the same nature with that
of Vitriol; and consequently this Saffron of Mars is no way differing
from Vitriol calcined to redness.
PROCESS V.
_Iron dissolved by the mineral Acids._
Put any mineral Acid whatever into a matrass with some water; set the
matrass on a sand-bath gently heated; drop into the vessel some filings
of Iron: the phenomena which usually accompany metalline dissolutions
will immediately appear. Add more filings, till you observe the Acid
hath lost all sensible action upon them: then remove your matrass from
the sand-bath; you will find in it a solution of Iron.
_OBSERVATIONS._
Iron is very easily dissolved by all the Acids. If you make use of the
Vitriolic Acid, care must be taken to weaken it with water, in case it
be concentrated; because the dissolution will succeed the better. The
vapours that rise on this occasion are inflammable; and if a lighted
paper be held to the mouth of the matrass, especially after keeping
it stopt for some time and shaking the whole gently, the sulphureous
vapours take fire with such rapidity as to produce a considerable
explosion; which is sometimes strong enough to burst the vessel into a
thousand pieces. This solution hath a green colour, and is in fact a
fluid Green Vitriol, which wants nothing but rest to make it shoot into
crystals.
If you make use of the Nitrous Acid, you must cease adding more filings
when the liquor, after standing still some moments, becomes turbid;
for, when this Acid is impregnated with Iron to a certain degree, it
lets fall some of that which it had dissolved, and becomes capable of
taking up fresh filings. Thus, by constantly adding new supplies of
Iron, this Acid may be made to dissolve a much greater quantity thereof
than is necessary to saturate it entirely. This solution is of a russet
colour, and doth not crystallize.
If the weather be not extremely cold, and the Acids have a proper
degree of strength, the sand-bath is unnecessary, as the dissolution
will succeed very well without it.
Iron dissolved by Acids may be separated therefrom, like all other
metallic substances in the same circumstances, either by the action
of fire, which carries off the Acid and leaves the Martial Earth, or
by the interposition of substances which have a greater affinity than
metallic substances have with Acids; that is, by Absorbent Earths
and Alkaline Salts. By whatever means you separate Iron from an Acid
solvent, it constantly appears, after the separation, in the form of
a yellowish red powder; because it is then deprived of most of the
phlogiston to which it owed its metalline form; whence it is reasonable
to think, that this is the proper colour of Martial earth.
All these precipitates of Iron are true Saffrons of Mars, which,
as well as those prepared by calcination, are so much the further
removed from the nature of a metal, the more they are deprived of
their phlogiston. Thence it comes that they are more or less soluble
by Acids, and more or less attracted by the magnet: as no ferruginous
earth, perfectly deprived of all inflammable matter, is at all
attracted by the magnet, or soluble by Acids.
CHAP. V.
_Of_ TIN.
PROCESS I.
_To extract Tin from its Ore._
Break your Tin ore into a coarse powder, and by washing carefully
separate from it all the heterogeneous matters, and ores of a different
kind, that may be mixed therewith. Then dry it, and roast it in a
strong degree of fire, till no more Arsenical vapour rise from it. When
the ore is roasted, reduce it to a fine powder, and mix it thoroughly
with twice its weight of the black flux well dried, a fourth part of
its weight of clean iron filings, together with as much borax and
pitch; put the mixture into a crucible; over all put Sea-salt to the
thickness of four fingers, and cover the crucible close.
Set the crucible thus prepared in a melting furnace: apply at first a
moderate and slow degree of fire, till the flame of the pitch, which
will escape through the joint of the cover, disappear entirely. Then
suddenly raise your fire, and urge it with rapidity to the degree
necessary for melting the whole mixture. As soon as the whole is in
fusion take the crucible out of the furnace, and separate the Regulus
from the scoria.
_OBSERVATIONS._
All Tin ores contain a considerable quantity of Arsenic, and no Sulphur
at all, or at most very little. Hence it comes that, though Tin be the
lightest of all metals, its ore is nevertheless much heavier than any
other; Arsenic being much heavier than Sulphur, of which the ores of
every other kind always contain a pretty large proportion. This ore is
moreover very hard, and is not brought to a fine powder with so much
ease as the rest.
These properties of Tin ore furnish us with the means of separating it
easily by lotion, not only from earthy and stony parts, but even from
the other ores which may be mixed with it. And this is of the greater
advantage on two accounts, _viz._ because Tin cannot endure, without
the destruction of a great part thereof, the degree of fire necessary
to scorify the refractory matters which accompany its ore; and again
because this metal unites so easily with Iron and Copper, the ores
of which are pretty commonly blended with Tin ore, that, after the
reduction, it would be found adulterated with a mixture of these two
metals, if they were not separated from it before the fusion.
But sometimes the Iron ore confounded with that of Tin is very heavy,
and is not easily pulverized; whence it comes to pass that it cannot be
separated therefrom by washing only. In that case the magnet must be
employed to separate it, after the ore hath been roasted.
Roasting is moreover necessary for Tin ore, in order to dissipate the
Arsenic which volatilizes, calcines, or destroys one part of the Tin,
and reduces the rest to a short, brittle substance, like a Semi-metal.
The ore is known to be sufficiently roasted when no more fumes rise
from it; when it has lost the smell of garlic; and when it does not
whiten a clean plate of Iron held over it.
Tin being one of those metals which are most easily calcined, it is
necessary in reducing its ore to employ such matters as may furnish it
with phlogiston. In order to defend it from the contact of the air,
which always accelerates the calcination of metallic substances, the
mixture is to be covered with Sea salt; and the addition of pitch helps
to increase the quantity of phlogiston.
PROCESS II.
_The Calcination of Tin._
Into an unglazed earthen dish put the quantity of Tin you intend to
calcine; melt it, and keep stirring it from time to time. Its surface
will be covered with a greyish white powder: continue the calcination
till all your Tin be converted into such a powder, which is the _Calx
of Tin_.
_OBSERVATIONS._
Though the calcination of metalline substances is promoted by exposing
them, in powder, or in filings, to the action of fire, and by ordering
it so that they may not melt, because they present a much smaller
surface when melted than when unmelted; yet we have not directed this
precaution to be used in calcining Tin. The reason is, this metal is so
fusible that it cannot endure the degree of fire requisite to destroy
its phlogiston without melting, and of course, though Tin calcines
easily, the operation is nevertheless tedious, because the melted metal
presents but a small surface to be acted on by the fire and the air.
This inconvenience may be partly remedied, and the operation greatly
expedited, by dividing the quantity of Tin to be calcined into several
small parcels, and exposing them to the fire in separate vessels, so
that they may not re-unite when melted, and form one single mass.
Leaf Tin cast on Nitre in actual fusion causes it to deflagrate and
fulminate; and from this mixture there rises a white vapour, which is
converted into flowers when it meets with any obstacle to impede its
flying off entirely.
Mr. Geoffroy, who went through a course of experiments on Tin, an
account whereof may be seen in the Memoirs of the Academy of Sciences,
found that from the colour of the calx of that metal a judgment may be
formed of its degree of purity, and nearly of the quantity and quality
of the metallic substances with which it is alloyed. The experiments
tried on this subject by that eminent Chymist are very curious.
He performed the calcination in a crucible, which he heated to a
cherry-red, and kept up the same degree of fire from the beginning to
the end of the operation. The calx which formed upon his metal, in that
degree of heat, appeared like small white scales, a little reddish on
the under side. He pushed it to one side as it formed, to the end that
it might not cover the surface of the metal, which, like all others,
requires the contact of the air to turn it into a calx.
"While he was making these calcinations, he had an opportunity of
observing a curious fact, of which no body before him had ever taken
notice; probably because no body had ever calcined Tin by the same
method. The fact is, that during the calcination of the Tin, whether
you break the pellicle which forms on the surface of the metal while
in red-hot fusion, or whether you let it remain without touching it,
you perceive in several places a small swell of a certain matter,
which bursts and makes its way through the pellicle. This matter puffs
up, grows red, at the same instant takes fire, and darts out a small
whitish flame, as vivid and as brilliant as that of Zinc, when urged
by a fire strong enough to sublime it into flowers. The vividness of
this flame may be further compared to that of several small grains of
phosphorus of urine fired and gently dropped on boiling water. From
this bright flame a white vapour exhales; after which the swelled mass
partly crumbles down, and turns to a light white powder, sometimes
spotted with red, according to the force of the fire. After this
momentary ignition, there arise stronger, more numerous, or more
frequent heavings of matter, out of which issues a good deal of white
fume, that may be intercepted by a cover of tin-plate or copper fitted
to the crucible, and appears to be the flowers of Tin, which in some
measure corrode these metals. Hence Mr. Geoffroy conjectures, with a
great deal of probability, that their sublimation is promoted by a
portion of Arsenic. When the crust formed by this calx comes to be too
thick, or in too great a quantity, to be pushed on one side, so as to
leave part of the metal uncovered, Mr. Geoffroy puts out the fire,
because no more calx would be formed: the communication of the external
air with the Tin in fusion being absolutely necessary thereto, as
hath been already said. In this operation it is to be observed that,
if the fire be too slow, neither the inflammation of the sulphureous
particles, nor the white fumes that rise, will be so distinctly
perceived, as when the fire is of the degree requisite to keep the
crucible just of a cherry-red heat.
"Mr. Geoffroy having taken off this first calx began the calcination
anew. In this second heat the buddings or heavings were more
considerable, and shot up in the form of cauli-flowers; but were still
composed of little scales. The thoroughly calcined portion of this
vegetation was likewise white and red; and the inferior surfaces of
some little bits thereof were wholly red. When these calcinations are
continued, sulphureous vapours rise seemingly of another kind than
those which appeared in the beginning; for all the calx made by the
first heat was perfectly white: whereas in the second it begins to be
spotted here and there with a tinge of black. Mr. Geoffroy was obliged
to go through a course of twelve several calcinations before he could
convert two ounces of Tin into a calx. He had the opportunity, during
these several calcinations, to observe that after the fourth, and
sometimes after the third, the red spots of the calx decrease, and the
black increase; that the germinations cease; that the crust of the calx
remains flat; that in the twelfth fire the Tin yields no more of this
scaly crust; that towards the end the undulations of the fused metal
appear no longer; and that the small remainder of calx is mixed with
several very minute grains of metal, which seem much harder than Tin.
Mr. Geoffroy could not collect a sufficient quantity thereof to cupel
them, and satisfy himself whether or no they were Silver."
Though Tin, and all the imperfect metals in general, seem converted
to a calx, and lose the metalline form, by one single calcination,
and that a slight one; yet they are not wholly deprived of their
phlogiston: for if the calx of Tin, for instance, prepared according
to the process above delivered, be cast upon Nitre in fusion, it will
make that salt deflagrate very perceptibly; a convincing proof that it
still contains much inflammable matter. If therefore a calx be required
absolutely free from phlogiston, this first calx must be recalcined
by a more violent fire, and the calcination continued till all the
phlogiston be dissipated.
"Mr. Geoffroy, being desirous of having his calx of Tin very pure and
perfectly calcined, exposed once more to the action of fire the twelve
portions of calx obtained by his former calcinations. But, as it would
have been too tedious to re-calcine them all separately, he made four
parcels of the whole, each consisting of three taken according to
the order in which they were first calcined; and gave to each a fire
sufficiently strong, and long enough continued, to calcine them as
thoroughly as was possible. After this second calcination he found
them all of a most beautiful white, except the first parcel: as that
consisted of the portions obtained by the three first heats, in all of
which there were scales tinged with red, it still retained a stain of
carnation, though hardly perceptible. Agreeably to the general rule,
the two ounces of Tin gained in weight by being thus calcined; and the
increase was two drams and fifty seven grains.
"Mr. Geoffroy observes, that no Tin, but what is absolutely pure, will
yield a perfectly white calx. He calcined in this manner several other
parcels of Tin that were impure and variously alloyed; each of which
produced a calx differently coloured, according to the nature and
quantity of its alloy: whence he justly concludes, that calcination
is a very good method of trying the fineness of Tin, or its degree of
purity." The particulars of Mr. Geoffroy's experiments on this subject,
which are very curious, may be seen in the Memoirs of the Academy for
1738.
It is proper to take notice that a man should be very cautious how he
exposes himself to the vapours of Tin, because they are dangerous; this
metal being very justly suspected by Chymists of containing something
Arsenical.
PROCESS III.
_The dissolution of Tin by Acids, The Smoking Liquor of_ Libavius.
Put into a glass vessel what quantity you please of fine Tin cut into
little bits. Pour on it thrice as much _aqua regis_, compounded of two
parts _aqua fortis_ weakened with an equal quantity of very pure water,
and one part Spirit of Salt. An ebullition will arise, and the Tin will
be very rapidly dissolved; especially if the quantities of metal and of
_aqua regis_ be considerable.
_OBSERVATIONS._
Tin is soluble by all the Acids; but _aqua regis_ dissolves it best
of any. Yet in this dissolution it comes to pass that part of the
dissolved Tin precipitates of its own accord to the bottom of the
vessel, in the form of a white powder. This solution of Tin is very fit
for preparing the purple-coloured precipitate of Gold. For this purpose
the solution of Tin must be let fall, drop by drop, into a solution of
Gold. Spirit of Nitre dissolves Tin nearly as _aqua regis_ does; but it
occasions a greater quantity of calx.
If two or three parts of Oil of Vitriol be poured on one part of Tin,
and if the vessel in which the mixture is made be exposed to such a
degree of heat as to evaporate all the moisture, there will remain
a tenacious matter sticking to the sides of the vessel. If water
be poured on this matter, and it be then exposed a second time to
the fire, it will dissolve entirely, excepting a small portion of
a glutinous substance, which also may be dissolved in fresh Oil of
Vitriol.
The Acid of Sea-salt may be combined with Tin by the following process.
Mix perfectly, by trituration in a marble mortar, an amalgam of two
ounces of fine Tin, and two ounces and a half of Quick-silver, with
as much Corrosive Sublimate. As soon as the mixture is completed, put
it into a glass retort, and distil with the same precautions as we
directed to be used in preparing concentrated and smoking Acids. There
will first come over into the receiver some drops of a limpid liquor,
which will be soon followed by an elastic spirit that will issue out
with impetuosity. At last some flowers, and a saline tenacious matter,
will rise into the neck of the retort. Then stop your distillation,
and pour into a glass bottle the liquor you will find in the receiver.
This liquor continually exhales a considerable quantity of dense, white
fumes, as long as it is allowed to have a free communication with the
air.
The product of this distillation is a combination of the Acid of
Sea-salt with Tin. As the affinity of Tin with this Acid is greater
than that of Mercury, the Acid contained in the Corrosive Sublimate
quits the Mercury, wherewith it was united, to join the Tin; which it
volatilizes so as to make it rise with itself in a limpid form. We make
use of the amalgam of Tin with Quick-silver, because we are thereby
enabled to mix the Corrosive Sublimate perfectly therewith, as the
success of the operation requires it should be.
In this experiment the Tin is volatilized, and the Acid of Sea-salt,
which is exceedingly concentrated, flies off incessantly in the form
of white vapours. This compound is known in Chymistry by the name of
_Smoking Liquor of Libavius_; a name derived from its quality, and from
its Inventor. Tin dissolved by Acids is easily separated from them by
Alkalis. It always precipitates in the form of a white calx.
CHAP. VI.
_Of_ LEAD.
PROCESS I.
_To extract Lead from its Ore._
Having roasted your Lead ore reduce it to a fine powder; mix it with
twice its weight of the black flux, and one fourth of its weight of
clean iron filings and borax; put the whole into a crucible capable of
containing at least thrice as much; over all put Sea-salt four fingers
thick; cover the crucible; lute the juncture; dry the whole with a
gentle heat, and set it in a melting furnace.
Make the crucible moderately red: you will hear the Sea-salt
decrepitate, and after the decrepitation a small hissing in the
crucible. Keep up the same degree of fire till that be over.
Then throw in as many coals as are necessary to complete the operation
entirely, and raise the fire suddenly, so as to bring the whole mixture
into perfect fusion. Keep up this degree of fire for a quarter of an
hour, which is time sufficient for the precipitation of the Regulus.
When the operation is finished, which may be known by the quietness of
the matter in the crucible, and by a bright vivid flame that will rise
from it, take the crucible out of the furnace, and separate the Regulus
from the scoria.
_OBSERVATIONS._
All Lead ore contains a good deal of Sulphur, which must be first
separated from it by roasting: and as this kind of ore is apt to fly
when first exposed to the fire, it is proper to keep it covered till it
be thoroughly heated. Another precaution to be used, in roasting this
ore, is not to give it too great a heat, but to keep the vessel which
contains it just moderately red; because it easily turns clammy, which
occasions it to stick to the vessel.
The Iron that is added, and mixed with the flux, absorbs the Sulphur
which may happen to remain, even after roasting: it helps also to
separate from the Lead some portions of semi-metal, especially of
Antimony, which are frequently mixed with this ore.
There is no fear least the Iron mix with the Lead in fusion, and
adulterate it: for these two metals are incapable of contracting any
union together, when each has its metalline form.
Nor is there any reason to apprehend lest the Iron should, by its
refractory quality, obstruct the fusion of the mixture; for though this
metal be not fusible when alone, yet, by the union it contracts with
the matters it is designed to absorb, it becomes so to such a degree as
in some measure to perform, on this occasion, the office of a flux.
The government of the fire is a point of great consequence in this
operation. It is necessary to apply but a moderate degree of heat
at first: for, when the metallic earth of the Lead, combining with
the phlogiston, acquires the metalline form, it swells up in such an
extraordinary manner, that there is great danger least the matter
should overflow, and run all out of the containing vessel. With a view
therefore to avoid this inconvenience, we direct a very large crucible
to be used. This heaving of the Lead, at the instant of its reduction,
is attended with a noise like the whistling of wind.
Notwithstanding all the precautions that can be used to prevent the
reduction from taking place too hastily, and so occasioning the
effusion of the matter, it often happens that, on raising the fire in
order to bring the mixture into fusion, the hissing suddenly begins
again, and is very loud. In that case all the apertures of the furnace
must immediately be shut close, in order to choak and suffocate the
fire: for, if this be neglected, the matter in the crucible will swell
up, make its way through the luting of the juncture, nay, push up the
cover, and run over. This accident is to be apprehended during the
first five or six minutes after you raise the fire in order to melt
the mixture. This effusion of the matter is accompanied with a dull
flame, a thick, grey and yellow smoke, and a noise like that of some
boiling liquor. When you observe these several phenomena you may be
sure the matter is run out of the crucible, either in the manner above
described, or by making its way through some cracks in the vessel, and
consequently that the operation is spoiled.
Moreover, this event infallibly follows whenever a bit of coal happens
to fall into the crucible; and this is one reason why it is necessary
to cover it.
You may be certain that the operation hath succeeded if the scoria be
smooth when cold, and have not in part escaped through the lute; if
the Lead be not dispersed in globules through the whole mass of the
matter contained in the crucible, but is, on the contrary, collected at
the bottom, in the form of a solid Regulus, not very shining, but of a
blueish cast, and ductile. Moreover, the scoria ought, in the present
case, to be hard and black, and should not appear full of holes like a
sieve, except only in that part which was contiguous to the Salt.
Here it is proper to observe, that the Sea-salt doth not mix with the
scoria, but floats upon it. After the operation it is black; which
colour it gets, no doubt, from the charred parts of the flux. The
absence of these signs shews the operation to have miscarried.
When the ore to be smelted is pyritose and refractory, it may be
roasted at first with a much stronger degree of fire than is used for
ores that are fusible; because the martial earth, and the unmetallic
earth, which are always mixed in pyritose matters, hinder it from
growing readily soft in the fire. Besides, such an ore requires a
greater quantity of the black flux and of borax to be mixed with it,
and a higher degree of fire to fuse it.
It is generally needless to mix iron filings with this sort of ore;
because the martial earth, with which pyritose matters are always
accompanied, is reduced during the operation by the help of the black
flux, which for that purpose is mixed with it in a large proportion,
and furnishes a quantity of iron sufficient to absorb the heterogeneous
minerals mixed with the Lead.
Yet, if it should be observed that the pyrites which accompany the Lead
ore are arsenical, then, as such pyrites contain but a small quantity
of ferruginous earth, iron filings must be added; which are, on this
occasion, so much the more necessary for absorbing the Arsenic, as
this mineral remains in part confounded with the ore, is reduced to
a Regulus during the operation, unites with the Lead, and destroys a
great deal of it by procuring its vitrification.
The Lead obtained from such pyritose ores is commonly not very pure; it
is blackish and scarce ductile; qualities communicated to it by a small
mixture of Copper in the pyrites, which always contain more or less
thereof. We shall presently shew the method of separating Lead from
Copper.
Lead ore may also be reduced by melting it amidst coals. For that
purpose first kindle a fire in the furnace in which you intend to melt
your ore; then put a layer of your ore immediately upon the lighted
coals, and cover it with another layer of coals.
Though the melting furnace used for this operation be capable of giving
a considerable heat, yet it is necessary further to increase the force
of the fire by the means of a good pair of perpetual bellows, which
will produce an effect like that of a forge. The ore melts, the earth
of the Lead unites with the phlogiston of the coals, and so is reduced
to metal, which runs through the coals, and falls into an earthen
vessel placed at the bottom of the furnace to receive it. Care must be
taken to keep this vessel well filled with charcoal-dust, to the end
that the Lead may be in no danger of calcination while it continues
there; the charcoal-dust constantly furnishing it with phlogiston to
preserve its metalline form.
The earthy and stony matters that accompany the ore are scorified by
this fusion, just as they are by the other which is performed in a
close vessel. With regard to the Sulphur and Arsenic, they are supposed
to have been first accurately separated from the ore by roasting. This
is the method commonly employed for smelting Lead ore at the works.
PROCESS II.
_To separate Lead from Copper._
With luting earth and charcoal-dust make a flat vessel, widening
upwards, and large enough to contain your metalline mass. Set it
shelving downwards from the back towards the fore-part; and in the
fore-part, at the bottom, make a little gutter communicating with
another vessel of the same nature, placed near the former and a little
lower. Let the mouth of the gutter within side the upper vessel be
narrowed, by means of a small iron plate fixed across it, while the
loam is yet soft; so as to leave a very small aperture, in the lower
part of this canal, sufficient to discharge the Lead as it melts. Dry
the whole by placing lighted coals around it.
When this apparatus is dry, put your mixed mass of Copper and Lead into
the upper vessel: both in that, and in the other vessel, light a very
gentle fire of wood or charcoal, so as not to exceed the degree of heat
necessary to melt Lead. In such a degree of heat the Lead contained
in the mixed mass will melt, and you will see it run out of the upper
vessel into the lower; at the bottom of which it will unite into a
Regulus. When in this degree of heat no more Lead flows, increase the
fire a little, so as to make the vessel moderately red.
When no more will run, collect the Lead contained in the lower vessel.
Melt it over again in an iron ladle, with a degree of fire sufficient
to make the ladle red; throw into it a little tallow or pitch, and
while it burns keep stirring the metal, in order to reduce any part of
it that may be calcined. Remove the pellicle or thin crust which will
form on the surface; squeeze out all the Lead it contains, and then put
it to the mass of Copper left in the upper vessel. Check the fire, and
in the same manner take off a second skin that will form on the surface
of the Lead. Lastly, when the metal is ready to fix, take off the skin
that will then appear on it. The Lead remaining after this will be very
pure, and free from all alloy of Copper.
With regard to the Copper itself, you will find it in the upper vessel
covered with a thin coat of Lead: and if the Lead mixed with it was in
the proportion of a fourth or a fifth part only, and the fire applied
was gentle and slow, it will retain nearly the same form after the
operation that the mixed mass had before.
_OBSERVATIONS._
Lead frequently remains mixed with Copper after the reduction of its
ore, especially if the ore was pyritose. Though Copper be a much more
beautiful and more ductile metal than Lead, yet the latter by being
alloyed with the former is rendered eager and brittle. This bad quality
is easily discovered by the eye on breaking it: for the surface of
the broken part appears all granulated; whereas when it is pure it is
more evenly, and resembles a congeries of solid angles. If the Lead
be alloyed with a considerable quantity of Copper, its colour hath a
yellowish cast.
Considering the bad qualities which Copper communicates to Lead, it
is necessary to separate these two metals from each other. The method
above laid down is the simplest and the best. It is founded on two
properties belonging to Lead: the first is that of being much more
fusible than Copper; so that it will melt and run in a degree of heat
that is not capable of making the Copper even red-hot, which yet is
very far from being able to melt it: the second is, that Lead, though
it hath an affinity with Copper, and unites very perfectly therewith,
yet is not able to dissolve it without a greater heat than the degree
barely necessary to fuse Lead. Hence it comes that Lead may be melted
in a Copper vessel, provided no greater degree of heat be applied than
that purpose requires. But when the Lead becomes so hot as to be red,
fume, and boil, it instantly begins to dissolve the Copper. For this
reason, it is essential to the success of our operation that a moderate
degree of heat only be applied, and no greater than is requisite to
keep the Lead in fusion.
Charcoal-dust is made an ingredient in the composition of the vessels
used on this occasion, in order to prevent the calcination of the Lead.
The iron plate, with which the entrance of the gutter within the upper
vessel is narrowed, serves to prevent the larger pieces of Copper,
which the Lead may carry along with it, from passing through: it stops
them, and allows the Lead to run off alone.
But as these parcels of Copper may entirely choak the passage, care
must be taken, when any happen to be stopt, to remove them from the
entrance of the gutter, and push them back into the middle of the
vessel. It is also necessary to observe whether or no the Lead fixes
any where in the passage; and, if it does, the heat of that part must
be increased, in order to melt it and make it run off.
Notwithstanding all the precautions that can be taken, to hinder the
melted Lead from carrying off any Copper with it, it is impossible to
prevent this inconvenience entirely; and therefore the Lead is melted
over again, in order to separate the small portion of Copper with which
it is still adulterated.
As Copper is much lighter than Lead, if these two metals happen to
be so blended together that the Copper, without being in fusion and
dissolved by the Lead, is only interposed between the parts of the
melted Lead, so as to swim therein, it is then precisely in the case of
a solid body plunged into a fluid heavier than itself, and must rise
to the surface, like wood thrown into water. It is proper to burn some
inflammable matter on this melted Lead, in order to reduce such parts
thereof as are constantly calcining on its surface while it is in
fusion; for without this precaution they would be taken off together
with the Copper.
The Copper remaining after this separation is, as we took notice
before, still mixed with a little Lead. If you desire to separate it
entirely therefrom, you must put it into a cupel, and expose it under
the muffle to such a degree of fire as may convert all the Lead into
litharge. This cannot be so done but that some of the Copper also
will be scorified by the heat of the fire, and by the action of the
Lead: but as there is a very great difference between the facility and
readiness with which these two metals calcine, the portion of Copper
that is calcined, while the whole Lead is turning into litharge, is
scarce worth considering.
The Lead, though carefully separated from the Copper by the process
here delivered, is not yet absolutely pure: sometimes it is alloyed
with Gold, and almost always contains some Silver. If you would free
the Lead as much as possible from any mixture of these two metals, you
must convert it into glass, separate the remaining bead, and afterwards
reduce this glass of Lead. But, as these two perfect metals are of no
prejudice to the Lead, it is not usual to separate them from it, unless
they be in a sufficient proportion to defray the charge, and produce
some profit besides.
When we examine by the cupel the just proportion of Gold and Silver
that an ore or a mixed metalline mass will yield, we make a previous
assay of the Lead to be employed in the operation, and afterwards, in
our estimate, deduct a proper allowance for the quantity of fine metal
due to the Lead made use of.
PROCESS III.
_The Calcination of Lead._
Take what quantity of Lead you please; melt it in one or more unglazed
earthen pans: a dark grey powder will be found on its surface. Keep
stirring the metal incessantly till it be wholly converted into such a
powder, which is the _Calx of Lead_.
_OBSERVATIONS._
As Lead is a very fusible metal, and in that respect greatly resembles
Tin, most of the observations we made on the calcination of Tin may be
applied here.
In the calcination of all metals, and particularly in this of Lead,
there appears a singular phenomenon which is not easily accounted for.
It is this: though these matters lose a great deal of their substance,
either by the dissipation of their phlogiston, or because some of the
metal, perhaps, exhales in vapours, yet when the calcination is over
their calces are found to be increased in weight, and this increase is
very considerable. An hundred pounds of Lead, for example, converted
into Minium, which is nothing but a calx of Lead brought to a red
colour by continuing the calcination, are found to gain ten pounds
weight; so that for an hundred pounds of Lead we have one hundred and
ten pounds of Minium: a prodigious and almost incredible augmentation,
if it be considered that, far from adding any thing to the Lead, we
have on the contrary dissipated part of it.
To account for this phenomenon Natural Philosophers and Chymists have
invented several ingenious hypotheses, but none of them entirely
satisfactory. As we have no established theory to proceed upon, we
shall not undertake to explain this extraordinary fact.
PROCESS IV.
_To prepare Glass of Lead._
Take two parts of Litharge, and one part of pure crystalline Sand;
mingle them together as exactly as possible, adding a little Nitre and
Sea-salt: put this mixture into a crucible of the most solid and most
compact earth. Shut the crucible with a cover that may perfectly close
it.
Set the crucible thus prepared in a melting furnace; fill the furnace
with coals; light the fire gradually, so that the whole may be slowly
heated: then raise the fire so as to make the crucible very red, and
bring the matter it contains into fusion; keep it thus melted for a
quarter of an hour.
Then take the crucible out of the furnace, and break it: in the bottom
thereof you will most commonly find a small button of Lead, and over
it a transparent Glass, of a yellow colour nearly resembling that of
amber. Separate this Glass from the little button of metal, and from
the saline matters which you will find above it.
_OBSERVATIONS._
Pure Lead, being exposed to a strong fire without any additament,
turns to Litharge; which is a scaly sort of substance, more or less
yellowish, shining, and soft to the touch. This is the first advance
to the Vitrification of Lead. The large refineries of Gold and Silver
by the means of Lead furnish a great quantity of this material. It is
sometimes whitish, and is then called _Litharge of Silver_; sometimes
yellow, and then bears the name of _Litharge of Gold_. The difference
of its colour depends on the degree of fire it hath undergone, and on
the metalline substances vitrified with it.
Litharge alone is very fusible, and being exposed to the fire is easily
converted into glass: but this Glass of Lead, made without additament,
is so active, so penetrating, and so apt to swell, that it can scarcely
be made use of when pure. We are obliged in some sort to clog it, by
uniting it with some vitrifiable matter that is not so subtile, such
as sand; and it is for this reason, not to render the mixture more
fusible, that we have directed the addition of one third part of Sand
to two thirds of Litharge.
The Nitre and Sea-salt, prescribed as ingredients in the mixture, are
designed to procure an equal fusion of the whole. For, as the sand is
lighter and less fusible than the Litharge, it will partly rise towards
the upper part of the crucible when that matter first begins to flow;
in consequence whereof the contents of the upper part will be much more
difficult to melt, and form a Glass much more compact than that below:
but the Nitre and Sea-salt possessing the upper part of the crucible,
because they are still lighter than the Sand, and being in their own
nature very efficacious fluxes, on account of their great fusibility,
they quickly bring about the fusion of those particles of sand, which,
having escaped the action of the Litharge, may have risen unvitrified
to its surface.
The most difficult thing to procure, and yet the most necessary to the
success of this operation, is a crucible of earth so firm and compact
as not to be penetrated by the Glass of Lead, which corrodes and makes
its way through every thing.
The precaution of chusing a crucible, that shall contain a good deal
more than the matter to be vitrified, is a necessary one, because
Litharge and Glass of Lead are very apt to swell.
The rule to keep the crucible close shut is also indispensably
necessary, to prevent any bit of charcoal, or other inflammable matter,
from falling into it: for when this happens it occasions a reduction of
the Lead, which is always attended with a sort of effervescence, and
such a considerable heaving, that commonly most of the mixture runs
over the crucible. For the same reason it is very proper, before you
expose the mixture to the fire, to examine whether or no it contains
any matter capable of furnishing a phlogiston during the operation; and
if it does, to remove that matter with great care.
The little button of Lead, found at the bottom of the crucible after
the operation, comes from a small portion of Lead that is commonly
left in Litharge, unless you prepare it carefully yourself, and do not
take it from the fire till you are sure of having destroyed all the
Lead. Besides, this small portion of Lead can be of no prejudice to the
operation, because it cannot communicate its phlogiston to the rest of
the matter.
The revivifying of Litharge, of the Calx, and of the Glass of Lead, may
be obtained by the same processes as the reduction of its ore.
PROCESS V.
_Lead dissolved by the Nitrous Acid._
Put into a matrass some _aqua fortis_ precipitated like that used to
dissolve Silver; weaken it by mixing therewith an equal quantity of
common water; set the matrass in a hot sand-bath; throw into it, little
by little, small bits of Lead, till you see that no more will dissolve.
_Aqua fortis_ thus lowered will dissolve about a fourth of its weight
of Lead.
There is gradually formed upon the Lead, as it dissolves, first a
grey powder, and afterwards a white crust, which at last hinder the
solvent from acting on the remaining part of the metal; and therefore
the liquor should be made to boil, and the vessel should be shaken to
remove those impediments, by which means all the Lead will be dissolved.
_OBSERVATIONS._
Lead very much resembles Silver, with respect to the phenomena which
attend its dissolution in Acids. For example, the Nitrous Acid must
be very pure and uncontaminated with the Vitriolic or Marine Acid, to
qualify it for keeping the Lead in solution: for, if it be mixed with
either the one or the other of these Acids, the Lead will precipitate
in the form of a white powder as fast as it dissolves; which is just
the case with Silver.
If the Vitriolic Acid be mixed with the Nitrous, the precipitate will
be a combination of the Vitriolic Acid with Lead; that is, a Neutral
Metallic Salt, or Vitriol of Lead. If the Acid of Sea-salt be mixed
therewith, the precipitate will be a _Plumbum corneum_; that is, a
Metallic Salt resembling the _Luna cornea_.
When all the Lead is dissolved as above described, the liquor appears
milky. If it be kept warm over the fire till little crystals begin to
appear on its surface, and afterwards left to stand quiet, in a certain
time there will be found at the bottom a greyish powder, which being
tried on Gold is Mercurial enough to whiten it. Little globules of
Quick-silver are even discernible in it.
We owe this observation, together with this manner of proving the
existence of Mercury in Lead, and of procuring it from thence, to M.
Grosse, who hath given an account of his process in the Memoirs of the
Academy of Sciences, from whence we have copied the description of the
operation in hand.
The solution being quickly poured off by inclination from the grey
mercurial precipitate is still milky, and deposites another white
sediment. When this second precipitate falls the liquor becomes clear
and limpid, and is then of a fine yellow colour, like a solution of
Gold. On this gold-coloured solution, and on the two precipitates
above-mentioned, M. Grosse made several observations, the chief of
which we shall here insert.
The yellow liquor affects the tongue at first with a taste of
sweetness; but afterwards vellicates it very smartly, and leaves on it
a strong sensation of acrimony, which continues for a long time.
Alkalis precipitate the Lead suspended in this liquor, just as they do
all other metals dissolved by Acids; and this precipitate of Lead is
white.
Sea-salt, or Spirit of Salt, separates the Lead from its solvent, and
precipitates it, as we observed before, into a _Plumbum corneum_: but
this precipitate differs from the _Luna cornea_, as being very soluble
in water; whereas the _Luna cornea_ will not dissolve in it at all;
or at least dissolves therein with great difficulty, and in a very
small quantity. This _Plumbum corneum_ dissolved in water is again
precipitated by the Vitriolic Acid. M. Grosse observes, that this
forms an exception to the eighth column of Mr. Geoffroy's Table of
Affinities; in which the Acid of Sea-salt is marked as having a greater
affinity than any other Acid with Metallic substances.
Our solution of Lead is also precipitated in a white powder by several
Neutral Salts; such as Vitriolated Tartar, Alum, and common Vitriol. It
is by the means of double affinities that these Neutral Salts effect
this precipitation.
Even pure water alone is capable of precipitating the Lead of our
solution, by weakening the Acid, and thereby disabling it from keeping
the metal suspended.
Lastly, as all the solutions of metals in Acids are nothing but
Neutral Metallic Salts in a fluid form, so if the solution of Lead be
evaporated over the fire, it will shoot into very beautiful crystals,
about the bigness of hemp-seed, shaped like regular pyramids having
square bases. These crystals are yellowish, and have a sweet saccharine
taste: but what is most singular in them is, that, as they consist of
the Nitrous Acid combined with Lead, which manifestly contains a great
deal of phlogiston, they constitute a Nitrous Metallic Salt, which has
the property of deflagrating in a crucible, without the addition of any
other inflammable matter. It is extremely hard to dissolve this Salt in
water.
The grey mercurial precipitate which whitens Gold, and in which little
globules of running Mercury are perceivable, is far from being pure
Mercury. This metallic substance makes but a small part thereof: for
it is an assemblage, 1. of little crystals of the same nature with
those afforded by the evaporated solution; 2. of a portion of the white
matter, or powder, which renders the solution milky; 3. of a grey
powder, which M. Grosse considers as the only mercurial part; 4. and
lastly, of little particles of Lead that have escaped the action of the
solvent; especially if a little more Lead than the Acid is capable of
dissolving were added with a view to saturate it entirely, as in the
present process.
By means of motion and heat the small parcels of Mercury may be
amalgamated with the Lead.
That Mercury should be found entire and in globules in the Spirit of
Nitre, which very easily dissolves that metallic substance, will not
be surprizing to those who reflect that, in the present case, the
Acid is saturated with Lead, with which it has a greater affinity
than with Mercury; as appears by M. Geoffroy's Table of Affinities,
where, in the column that hath the Nitrous Acid at top, Lead is placed
above Mercury. Agreeably to this, if Lead be presented to a solution
of Mercury in Spirit of Nitre, the Lead will be dissolved, and as the
dissolution thereof advances the Mercury will precipitate.
Hence it appears that, in order to find any Mercury in the spontaneous
precipitate of Lead dissolved by the Nitrous Acid, it is necessary that
the Acid be entirely saturated with Lead; or else that portion of the
Acid which remains unsaturated will dissolve the Mercury.
With regard to the white powder that renders the solution milky, and
afterwards precipitates, it is nothing but a portion of the Lead,
which, not being intimately united with the Acid, falls in part of its
own accord. It is a sort of calx of Lead, which being exposed to the
fire becomes partly glass, and partly Lead, because it still retains
some of its phlogiston.
CHAP. VII.
_Of_ MERCURY.
PROCESS I.
_To extract Mercury from its Ore, or to revivify it from Cinabar._
Pulverize the Cinabar from which you would extract the Mercury; with
this powder mix an equal part of clean iron filings; put the mixture
into a retort of glass or iron, leaving at least one third part thereof
empty. Set the retort thus prepared in a sand-bath, so that its body
may be quite buried in the sand, and its neck decline considerably
downwards: fit on a receiver half filled with water, and let the nose
of the retort enter about half an inch into the water.
Heat the vessels so as to make the retort moderately red. The Mercury
will rise in vapours, which will condense into little drops, and fall
into the water in the receiver. When you see that nothing more comes
over with this degree of heat, increase it, in order to raise what
Mercury may still be left. When all the Mercury is thus brought over,
take off the receiver, pour out the water contained in it, and collect
the Mercury.
_OBSERVATIONS._
Mercury is never mineralized in the bowels of the earth by any thing
but Sulphur; with which it forms a compound of a brownish red colour,
known by the name of _Cinabar_.
Sometimes it is only mixed with earthy and stony matters that contain
no Sulphur; but, as this metallic substance is never destitute of its
phlogiston, it then has its metalline form and properties. When it is
found in this condition, nothing is more easy than to separate it from
those heterogeneous matters. For that purpose no more is requisite than
to distil the whole with a fire strong enough to raise the Mercury in
vapours. This mineral is volatile; the earthy and stony matters are
fixed; and a certain degree of heat will effect a complete separation
of what is volatile from what is fixed.
This is not the case when Mercury is combined with Sulphur: for this
latter mineral is volatile as well as Mercury; and the compound
resulting from the union of them both is also volatile: so that if
Cinabar were exposed to the fire in close vessels, as it must be to
save the Mercury, it would be sublimed in substance, without being
decomposed at all.
In order therefore to separate these two substances from each other,
we must have recourse to the interposition of some third, which hath a
greater affinity with one of them than the other hath, and no affinity
with that other.
Iron hath all the conditions requisite for this purpose; seeing it
hath, as may be seen in the Table, a much greater affinity with Sulphur
than Mercury hath, and is incapable of contracting any union with
Mercury.
Iron, however, is not the only substance that may be employed on this
occasion: Fixed Alkalis, Absorbent earths, Copper, Lead, Silver,
Regulus of Antimony, have all, as well as Iron, a greater affinity
than Mercury with Sulphur. Nay, several of these substances, namely,
the saline and earthy Alkalis, as well as Regulus of Antimony, cannot
contract any union with Mercury: the rest, to wit, Copper, Lead, and
Silver, are indeed capable of amalgamating with Mercury; but then the
union which these metals contract with the Sulphur prevents it; and
even though they should unite with this metallic substance, the degree
of heat to which the whole mixture is exposed would soon carry up the
Mercury, and separate it with ease from those fixed substances.
In this distillation the same cautions must be observed as in all
others: that is, the vessels must be slowly heated, especially if a
glass retort be used; the fire must be raised by degrees, and a much
stronger one applied at last than at first. This operation particularly
requires a very strong degree of fire, when there is but a small
quantity of Mercury left.
After the operation there remains in the retort a compound of Iron and
Sulphur, which may easily be converted into a _crocus_, by calcining it
and burning away the Sulphur.
If a Fixed Alkali be employed, a Liver of Sulphur will be found in the
retort after the distillation.
If the Cinabar from which you extract the Mercury be good, you will
generally obtain seven eighths of its weight in Quick-silver.
In the present operation it is not necessary to lute on the receiver,
because the water, in which the nose of the retort is plunged, is
sufficient to fix the Mercurial vapours. In case the Cinabar, from
which you intend to separate the Mercury, be mixed with a great
quantity of heterogeneous, but fixed, matters, such as earths, stones,
&c. it may be separated from them by subliming it with a proper degree
of heat, because it is volatile.
The vapours of Mercury are prejudicial, and may excite a salivation,
tremors, and palsies; they should therefore be always avoided by such
as work on this mineral.
The oldest and richest mine of Mercury is that of Almaden in Spain.
It is a singular property of that mine that, though the Mercury found
in it is combined with Sulphur, and in the form of Cinabar, yet no
additament is required to procure the separation of these two; the
earthy and stony matter, with which the particles of the ore are
incorporated, being itself an excellent absorbent of Sulphur.
In the Quick-silver works carried on at this mine they make no use
of retorts. They place lumps of the ore on an iron grate, which
stands immediately over the furnace. The furnaces which serve for
this operation are closed at the top by a sort of dome, behind which
stands the shaft of a chimney that communicates with the fire-place,
and gives vent to the smoke. These furnaces have in their fore-side
sixteen apertures, to each of which is luted an aludel in a horizontal
position, communicating with a long row of other aludels placed
likewise in an horizontal direction; which aludels so connected
together form one long pipe or canal, the further end whereof opens
into a chamber destined to receive and condense all the mercurial
vapours. These rows of aludels are supported from end to end by a
terrass, which runs from the body of the building, wherein the furnaces
are erected, to that where the chambers are built that perform the
office of receivers.
This is a very ingenious contrivance and saves much labour, expence,
and trouble, that would be unavoidable if retorts were employed.
That part of the furnace which contains the lumps of ore, serves for
the body of the retort; the row of aludels for its neck; and the little
chambers in which these canals terminate are actual receivers. The
terrass of communication, which reaches from the one building to the
other, is formed of two inclined planes, the lower edges of which,
meeting in the middle of the terrass, rise from thence insensibly; the
one quite to the building where the furnaces are, and the other to that
which forms the recipient chambers. By this means, when any Mercury
escapes through the joints of the aludels, it naturally runs down
along these inclined planes, and so is collected in the middle of the
terrass, where the inferior sides of the planes meeting together form a
sort of canal, out of which it is easily taken up.
The celebrated M. de Jussieu having viewed the whole himself, in a
journey he made to this mine, furnished us with this description of the
work.
PROCESS II.
_To give Mercury, by the action of Fire, the appearance of a Metalline
Calx._
Put Mercury into several little glass matrasses with long and narrow
necks. Stop the matrasses with a little paper, to prevent any dirt from
falling into them. Set them all in one sand-bath, so that they may
be surrounded with sand as high as two thirds of their length. Apply
the strongest degree of heat that Mercury can bear without subliming:
continue this heat without interruption, till all the Mercury be turned
to a red powder. The operation lasts about three months.
_OBSERVATIONS._
Mercury treated according to the process here delivered hath all
the appearance of a metalline calx, but it hath no more: for, if it
be exposed to a pretty strong degree of fire, it sublimes, and is
wholly reduced to running Mercury, without the addition of any other
inflammable matter; which proves that during this long calcination it
lost none of its phlogiston.
The volatile nature of Mercury, which permits it not to bear a heat
of any strength without subliming, prevents our examining all the
effects that fire is capable of producing on it. Yet there is reason
to believe that, as this metallic substance resembles the perfect
metals in its weight, its splendour, and a brilliancy which resists all
the impressions of the air without alteration, it would like them be
unchangeable by the greatest force of fire, if it were fixed enough to
bear it.
In order to give Mercury the form of a metalline calx, it must
necessarily be exposed for about three months together, to the utmost
heat it can bear without subliming, as is above directed. Boerhaave
kept it digesting in a less heat for fifteen years successively, both
in open and in close vessels, without observing it to suffer the least
change; except that there was formed upon its surface a small quantity
of a black powder, which was reduced to running Mercury by trituration
alone.
Mercury thus converted to a red powder is known in chymistry and
medicine by the name of _Mercury precipitated per se_: a title proper
enough, as it is actually reduced to the form of a precipitate, and
that without any additament; but very improper on the other hand,
considering, that in reality this Mercury is not a precipitate, as not
having been separated from any menstruum in which it was dissolved.
PROCESS III.
_To dissolve Mercury in the Vitriolic Acid. Turbith Mineral._
Put Mercury into a glass retort, and pour on it thrice its weight of
good Oil of Vitriol. Set the retort in a sand-bath; fit on a recipient;
warm the bath by degrees till the liquor just simmer. With this heat
the Mercury will begin to dissolve. Continue the fire in this degree
till all the Mercury be dissolved.
_OBSERVATIONS._
The Vitriolic Acid dissolves Mercury pretty well: but for this purpose
the Acid must be very hot, or even boil; and then too it is a very
long time before the dissolution is completed. We have directed the
operation to be performed in a retort; because this solution is usually
employed to make another preparation called _Turbith Mineral_, which
requires that as much as possible of the Acid solvent be abstracted by
distillation. Having therefore dissolved your Mercury in the Vitriolic
Acid, if you will now prepare the Turbith, you must, by continuing
to heat the retort, drive over all the liquor into the receiver, and
distil till nothing remains but a white powdery matter: then break
the retort; pulverize its contents in a glass mortar, and thereon
pour common water, which will immediately turn the white matter of a
lemon-colour; wash this yellow matter in five or six warm waters, and
it will be what is called in medicine _Turbith Mineral_; that is, a
combination of the Vitriolic Acid with Mercury, five or six grains
whereof is a violent purgative, and also an emetic; qualities which
it possesses in common with the Vegetable Turbith, whose name it hath
therefore taken.
There rises out of the retort, both while the Mercury is dissolving,
and while the solvent is abstracting, a weak Spirit of Vitriol; because
a great part of the Acid remains united with the Quick-silver, which
at last appears in the form of a white powder: so that, if you do not
incline to save the Acid which rises on this occasion, you may, instead
of drawing off the liquor in a retort, evaporate it in a glass bason
set on a sand-bath, which will be much sooner done.