This substance affords a striking instance how readily one may be
deceived in giving names without proper examination. Our alum was
certainly not known to the Greeks or the Romans; and what the latter
called _alumen_[487] was vitriol, (the green sulphate of iron)[488];
not however pure, but such as forms in mines. To those who know
how deficient the ancients were in the knowledge of salts, and of
mineralogy in general, this assertion will without further proof appear
highly probable[489]. Alum and green vitriol are saline substances
which have some resemblance; both contain the same acid called the
vitriolic or sulphuric; both have a strong astringent property, and on
this account are often comprehended under the common name of styptic
salts; and both are also not only found in the same places, but are
frequently obtained from the same minerals. The difference, that the
vitriols are combinations of sulphuric acid with a metallic oxide,
either that of iron, copper or zinc, and alum on the other hand with
a peculiar white earth, called on this account alumina, has been
established only in modern times[490].
A stronger proof however in favour of my assertion, is what
follows:--The Greeks and the Romans speak of no other than natural
alum; but our alum is seldom produced spontaneously in the earth, and
several of our most accurate mineralogists, such as Scopoli and Sage,
deny the existence of native alum[491]. Crystals of real alum are
formed very rarely on minerals which abound in a great degree with
aluminous particles, when they have been exposed a sufficient time
to the open air and the rain; and even then they are so small and so
much scattered, that it requires an experienced and attentive observer
to know and discover them. The smallest trace of alum-works is not
to be found in the ancients, nor even of works for making vitriol
(sulphate of iron), except what is mentioned by Pliny, who tells us
that blue vitriol was made in Spain by the process of boiling; and
this circumstance he considers as the only one of its kind, and so
singular, that he is of opinion no other salt could be obtained in
the same manner[492]. Besides, everything related by the ancients of
their alum agrees perfectly with native vitriols: but to describe them
all might be difficult; for they do not speak of pure salts, but of
saline mixtures, which nature of itself exhibits in various ways, and
under a variety of forms; and every small difference in the colour,
the exterior or interior conformation, however accidental, provided
it could be clearly distinguished, was to them sufficient to make a
distinct species, and to induce them to give it a new name[493].
The celebrity which the ancient alum had, as a substance extremely
useful in dyeing and medicine, was entirely forgotten when the alum of
the moderns became known; but this celebrity was again revived when
it was discovered that real alum could be often made from minerals
containing sulphur compounds; or that where the latter are found
there are generally minerals which abound with it. In many of these
places alum-works have in the course of time been erected; and this
circumstance has served in some measure to strengthen the opinion that
the alum of the ancients and that of the moderns are the same salt;
because where the former was found in ancient times, the latter has
since been procured by a chemical process. Some historians of the
fifteenth century even speak of the alum-works erected at that period,
as if the art of making this salt had only been revived in Europe.
The ancients procured their alum from various parts of the world.
Herodotus mentions Egyptian alum; for he tells us that when the people
of Delphos, after losing their temple by a fire, were collecting a
contribution in order to rebuild it, Amasis king of Egypt sent them a
thousand talents of alum[494]. In Pliny’s time the Egyptian alum was
accounted the best. It is well known that real alum is reckoned among
the exports of Egypt at present, but I am acquainted with no author
who mentions the place where it is found or made, or who has described
the method of preparing it.
The island of Melos, now called Milo, was particularly celebrated
on account of its alum, as we learn from Diodorus Siculus, Celsus,
Pliny and others, though none was to be found there in the time of
Diodorus[495]. This native vitriol has been observed in the grottos of
that island by several modern travellers, especially Tournefort[496],
who very properly considers it as the real alum of the ancients.
The islands of Lipara and Strongyle, or, as they are called at present,
Lipari and Stromboli, contained so great a quantity of this substance,
that the duty on it brought a considerable revenue to the Romans[497].
At one period, Lipari carried on an exclusive trade in alum, and raised
the price of it at pleasure; but in that island at present there
are neither vitriol nor alum-works. Sardinia, Macedonia, and Spain,
where alum was found formerly, still produce a salt known under that
name[498].
When our alum became known, it was considered as a species of the
ancient; and as it was purer, and more proper to be used on most
occasions, the name of alum[499] was soon appropriated to it alone. The
kinds of alum however known to the ancients, which were green vitriol,
maintained a preference in medicine and for dyeing black; and on this
account, these impure substances have been still retained in druggists’
shops under the name of _misy_, _sory_, &c. But a method was at length
found out of procuring thence crystallized martial salts (salts of
iron), which obtained the new name of _vitriol_. This appellation had
its rise first in the eleventh or twelfth century; at least I know no
writer older than Albertus Magnus by whom it is mentioned or used.
Agricola conjectures that it was occasioned by the likeness which
the crystals of vitriol had to glass. This is also the opinion of
Vossius[500]; and it is very singular that Pliny says nearly the same
thing; for he observes, speaking of blue vitriol, the only kind then
known, that one might almost take it for glass[501].
By inquiring into the uses to which the ancients applied their alum, I
find that it was sometimes employed to secure wooden buildings against
fire. This remark I have here introduced to show that this idea, which
in modern times has given occasion to many expensive experiments, is
not new. Aulus Gellius[502] relates, from the works of an historian now
lost, that Archelaus, one of the generals of Mithridates, washed over
a wooden tower with a solution of alum, and by these means rendered
it so much proof against fire, that all Sylla’s attempts to set it in
flames proved abortive. Many have conjectured that the substance used
for this purpose was neither vitriol nor our alum, but rather asbestos,
which is often confounded with Atlas-vitriol[503]; and against this
mistake cautions are to be found even in Theophrastus. But it may be
asked, With what was the asbestos laid on? By what means were the
threads, which are not soluble in water, made fast to the wood? How
could a tower be covered with it? I am rather inclined to believe, that
a strongly saturated solution of vitriol might have in some measure
served to prevent the effects of the fire, at least as long as a thin
coat of potters’ earth or flour-paste, which in the present age have
been thought deserving of experiments attended with considerable
expense. It does not however appear that the invention of Archelaus,
which is still retained in some old books[504], has been often put in
practice[505]; for writers on the art of war, such, for example, as
Æneas, recommended vinegar to be washed over wood, in order to prevent
its being destroyed by fire.
I shall now proceed to the history of our present alum, which was
undoubtedly first made in the East. The period of the invention I
cannot exactly determine, but I conclude with certainty that it is
later than the twelfth century[506]; for John, the son of Serapion,
who lived after Rhazes, was acquainted with no other alum than the
impure vitriol of Dioscorides[507]. What made the new alum first and
principally known was its beneficial use in the art of dyeing, in
which it is employed for fixing as well as rendering brighter and
more beautiful different colours. This art therefore the Europeans
learned from the Orientals, who, even yet, though we have begun to
apply chemistry to the improvement of dyeing, are in some respects
superior to us, as is proved by the red of Adrianople, their silks and
their Turkey leather. The Italians procured their first alum from the
Levant, along with other materials for dyeing; but when these countries
were taken possession of by the Turks, it grieved the Christians to be
obliged to purchase these necessary articles from the common enemy, and
bitter complaints on that subject may be seen in the works of various
authors. In the course of time the Italians became acquainted with the
art of boiling alum; for some of them had rented Turkish alum-works,
and manufactured that salt on their own account. They at length
found aluminous minerals in their own country, on which they made
experiments. These having answered their expectations, they were soon
brought into use; and this branch of trade declined afterwards so much
in Turkey, that many of the alum-works there were abandoned.
We are told by many historians that the Europeans who first made alum
in Italy learned their art, as Augustin Justinian says, at Rocca di
Soria, or Rocca in Syria. Neither in books of geography nor in maps,
however, can I find any place of this name in Syria. I at first
conjectured that Rocca on the Euphrates might be here meant, but at
present it appears to me more probable that it is Edessa, which is
sometimes called Roha, Raha, Ruha, Orfa, and also Roccha, as has been
expressly remarked by Niebuhr[508]. Edessa is indeed reckoned to be in
Mesopotamia, but some centuries ago Syria perhaps was understood in
a more extended sense. This much at least is certain, that minerals
which indicate alum have been often observed by travellers in that
neighbourhood.
It appears that the new alum was at first distinguished from the
ancient vitriol by the denomination of _Rocca_, from which the French
have made _alun de roche_, and some of the Germans _rotzalaun_[509].
Respecting the origin of this name very different conjectures have
been formed. Some think it is derived from _rocca_, which in the Greek
signifies a rock, because this salt is by boiling procured from a
stone; and these translate the word _alumen rupeum_, from which the
French name is formed[510]. Some are of opinion that alum obtained from
alum-stone has been so called to distinguish it from that procured from
schists, which is generally mixed with more iron than the former[511];
and others maintain that alum acquired the name of _Rocca_ from the
alum-rocks in the neighbourhood of Tolfa[512]. It is to be remarked,
on the other hand, that Biringoccio, that expert Italian, confesses
he does not know whence the name has arisen[513]. For my part I am
inclined to adopt the opinion of Leibnitz, that _alumen roccæ_ was
that kind first procured from Rocca in Syria; and that this name was
afterwards given to every good species of alum, as we at present call
the purest Roman alum[514].
In the fifteenth century there were alum-works in the neighbourhood
of Constantinople, from which John di Castro, of whom I shall have
occasion to speak hereafter, learned his art. May not these alum-works
be those visited by Bellon, and of which he has given an excellent
description[515]? He names the place _Cypsella_ or _Chypsilar_, and
says that the alum in commerce is called _alumen Lesbium_, or _di
Metelin_. The alum procured from Constantinople at present may perhaps
be brought from the same spot; but I am not sufficiently acquainted
with its situation to determine that point with certainty, for Büsching
makes no mention of it. In some maps I find the names _Ypsala_ and
_Chipsilar_ on the western side of the river Mariza, Maritz or
Maricheh, which was the Hebrus of the ancients; in others stands the
name _Scapsiler_ on the west bank of the sea Bouron; and it is not
improbable that these may be all derived from the old _Scaptesyle_ or
_Scapta Hyla_, where, according to the account of Theophrastus, Pliny
and others, there were considerable mines.
Another alum-work, no less celebrated in the fifteenth century, was
established near the city _Phocæa Nova_, at present called _Foya Nova_,
not far from the mouth of the Hermus, in the neighbourhood of Smyrna.
Of this work, Ducas, who had a house there, has given a particular
description, from which we learn that in his time, that is under the
reign of Michael Palæologus, it was farmed by Italians, who sold the
produce of it to their countrymen, and to the Dutch, French, Spaniards,
English, Arabs, Egyptians, and people of Syria. This author relates
very minutely in what manner the alum was made, but that work has been
long since abandoned[516]: alum however made in the neighbourhood is
still exported from Smyrna[517]. It is much to be wished that ingenious
travellers would examine the alum-works in Thrace, around Smyrna,
and in Turkey in general, and give an accurate description of them
according to the state in which they are at present[518].
The oldest alum-works in Europe were established about the middle
of the fifteenth century, but where they were first erected cannot
with certainty be ascertained; for it appears that several were set
on foot in different places at the same period. Some affirm that the
first alum made in Europe was manufactured in the island Ænaria, or
Pithacusa, at present called Ischia, by a Genoese merchant, whom
some name Bartholomew Perdix, and others Pernix. This man, who is
praised on account of his ingenuity and attachment to the study of
natural history, having often travelled through Syria, learned the
method of boiling alum at Rocca; and on his return found alum-stones
among the substances thrown up by the eruption of a volcano which had
destroyed part of the island, and gave occasion to their being first
employed in making that salt. Such is the account of respectable
historians, Pontanus[519], Bizaro[520], Augustine Justinian[521], and
Bottone[522], who wrote much later. Bizaro says that this happened in
the year 1459, which agrees perfectly with the account of Pontanus; for
he tells us that it was under the reign of Ferdinand I., natural son of
Alphonsus, who ascended the throne in 1458. Besides, the earthquake,
which had laid waste the island one hundred and sixty-three years
before, took place in 1301, which makes the time of this invention to
fall about the year 1464. So seems Bottone also to have reckoned, for
he mentions expressly the year 1465.
The alum-work which is situated about an Italian mile northwest from
Tolfa, and six from Civita Vecchia, in the territories of the Church,
is by some Italian historians reckoned to have been the first. However
this may be, it is certain that it is the oldest carried on at present.
The founder of it was John di Castro, a son of the celebrated lawyer,
Paul di Castro[523], who had an opportunity at Constantinople, where
he traded in Italian cloths and sold dye-stuffs, of making himself
acquainted with the method of boiling alum. He was there at the
time when the city fell into the hands of the Turks; and after this
unfortunate event, by which he lost all his property, he returned to
his own country. Pursuing there his researches in natural history,
he found in the neighbourhood of Tolfa a plant which he had observed
growing in great abundance in the aluminous districts of Asia: from
this he conjectured that the earth of his native soil might also
contain the same salt; and he was confirmed in that opinion by its
astringent taste. At this time he held an important office in the
Apostolic Chamber; and this discovery, which seemed to promise the
greatest advantages, was considered as a real victory gained over the
Turks, from whom the Italians had hitherto been obliged to purchase all
their alum. Pope Pius II., who was too good a financier to neglect such
a beneficial discovery, caused experiments to be first made at Viterbo,
by some Genoese who had formerly been employed in the alum-works in
the Levant, and the success of them was equal to his expectations.
The alum, which was afterwards manufactured in large quantities, was
sold to the Venetians, the Florentines, and the Genoese. The Pope
himself has left us a very minute history of this discovery, and of the
circumstances which gave rise to it[524]. Some pretend that Castro was
several years a slave to a Turk who traded in alum[525]; others affirm
that he had even been obliged to labour as a slave in alum-works[526];
and others, that he learned the art of boiling alum from a citizen of
Corneto, a town in the dominions of the Pope, and from a Genoese, both
of whom had acquired their knowledge in the Levant[527]. But as I do
not wish to ascribe a falsehood to the Pontiff, I am of opinion that
the history of this discovery must have been best known to him. He has
not, indeed, established the year with sufficient correctness; but we
may conclude from his relation that it must have been 1460 or 1465. The
former is the year given by Felician Bussi; and the latter that given
in the history of the city of Civita Vecchia.
The plant which first induced John di Castro to search for alum was
that evergreen, prickly shrub, the _Ilex aquifolium_, or holly, which
in Italy is still considered as an indication that the regions where
it grows abound with that salt. But though it is undoubtedly certain
that the quality of the soil may be often discovered by the wild plants
which it produces, it is also true that this shrub is frequently found
where there is not the smallest trace of alum; and that it is not to be
seen where the soil abounds with it, as has been already remarked by
Boccone[528] and Tozzetti[529].
Among the earliest alum-works may be reckoned that which was erected
at Volterra, in the district of Pisa, in 1458, by a Genoese named
Antonius[530]. Others say that it was constructed by an architect of
Sienna; but this opinion has perhaps arisen only from the work having
been farmed by a citizen of Sienna, or built at his expense. On account
of this alum-work an insurrection of the inhabitants of Volterra broke
out in 1472; but it was at length quelled by the Florentines, who took
and plundered the city[531]. Brutus, who wrote his History of Florence
in the year 1572, says that this alum-work was carried on in his time:
but this is certainly false; for Raphael di Volterra[532], who died
in 1521 in his native city, expressly tells us that in his time alum
was no longer boiled there; and this is confirmed by Baccius[533], who
also lived in the sixteenth century. At present no remains of it are
left; so that Tozzetti was not able to discover the place where the
alum-stones were broken[534].
It appears from what has been said, that the art of boiling alum in
Europe was first known in Italy, but not before the year 1548. That
document therefore of the year 1284, quoted by Tozzetti, and in which
alum-works, _alumifodinæ_, are mentioned, must, as he himself thinks,
be undoubtedly false[535].
The great revenue which the Apostolical Chamber derived from alum,
induced many to search for aluminous minerals, and works were erected
wherever they were found. Several manufactories of this substance
were established therefore in various parts, which are mentioned by
Baccius[536], Biringoccio, and other writers of the sixteenth century.
The pope however understood his own interest so well, that he never
rested until he had caused all the works erected in the territories of
others to be given up, and until he alone remained master of the prize.
He then endeavoured by every method possible to prevent foreigners from
acquiring an accurate knowledge of the art of boiling alum; and at the
same time found means, by entering into commercial treaties with other
nations, and by employing the medium of religion, which has always the
greatest effect on weak minds, to extend his commerce in this article
more and more. The price was raised from time to time, and it at length
became so high that foreigners could purchase this salt at a cheaper
rate from the Spaniards, and even when they sent for it to Turkey. His
Holiness, that he might convert this freedom of trade into a sin, and
prevent it by the terror of excommunication, artfully gave out that
he meant to set apart the income arising from his alum-works to the
defence of Christianity; that is, towards carrying on war against the
Turks. Prohibitions and threats now followed in case any one should be
so unchristian as to purchase alum from the Infidels; but every person
was at liberty to make what bargain he could with his Holiness for this
commodity.
In the year 1468 Pope Paul II. entered into a commercial treaty
respecting alum with Charles the Bold, duke of Burgundy; but in 1504
Roman alum had risen to such an exorbitant price, that Philip the Fair,
archduke of Austria, caused a council of inquiry to be held at Bruges,
by which it appeared that this article could be purchased at a much
cheaper rate in Turkey. Commissions therefore were sent thither for
that purpose; but scarcely was this known at Rome, when a prohibition,
under pain of excommunication, was issued by Pope Julius II. This
pontiff however was not the only one from whom such prohibitions
proceeded: bulls of the like kind were issued also by Julius III., Paul
III., Paul IV., Gregory XIII. and others[537].
But these means, like all those founded on the simplicity of others,
could not be of long duration; and as soon as men became a little more
enlightened, they learned to know their own interest, and to discover
the selfishness of the Pope’s bulls. Unless Biringoccio, who visited
a part of the German mines, be under a mistake, the first European
alum-work out of Italy was erected in Spain; and is that still carried
on with considerable profit at Almacaron, not far from Carthagena[538].
In the beginning of the sixteenth century very large quantities of alum
were brought to Antwerp, as we learn from Guicciardini’s Description of
the Netherlands.
At what time the first alum-work was erected in Germany, I am not
able to determine; but it appears that alum began to be made at
Oberkaufungen in Hesse in the year 1554. For the alum-work at Commotau
in Bohemia, the first letters-patent were granted in 1558. An alum-work
was established at Lower Langenau in the county of Glatz in 1563; but
it was soon after abandoned. Several other manufactories of alum are
mentioned by Agricola, such as that of Dieben or Duben, in the circle
of Leipsic, and those of Dippoldiswalda, Lobenstein, &c.
In England the first alum-work was erected at Gisborough in Yorkshire,
in the reign of queen Elizabeth; though Anderson[539] says in 1608.
Sir Thomas Chaloner, who had an estate there, conjecturing from the
nature of the plants which grew wild that there must be minerals in the
neighbourhood, after making some search, at length discovered alum.
As there was however no one in England at that time who understood
the method of preparing it, he privately engaged workmen belonging to
the Pope’s alum-works; and it is said, that as soon as the Pontiff
heard this, he endeavoured to recall them by threats and anathemas.
These however did no injury to the heretics; and in a little time the
alum-work succeeded so well, that several more of the same kind were
soon after established[540]. But what more dishonoured the Pontiff’s
denunciations was, that in later times the proprietors of the English
alum-works farmed those of the Apostolic Chamber, and increased in
various ways the benefit derived from them[541].
At what period alum-works were established in other countries I
have not been able to learn. I however know that one was erected at
Andrarum[542] in Sweden in 1630.
[The process for obtaining alum from the alum-stone of Tolfa, which
is also found in Hungary, Auvergne, and other parts of the world, and
which contains _all_ the ingredients requisite for the production of
alum, has been fully described. The greater portion however of the
alum manufactured in this country is obtained from alum-slate,--a
bituminous schist containing iron-pyrites (sulphuret of iron) diffused
in extremely fine particles throughout its mass. Many of these schists
crumble to pieces when they are exposed to the air; the sulphur of the
pyrites becomes gradually converted by the absorption of oxygen from
the atmosphere into sulphuric acid, while, at the same time, the iron
is peroxidized, and having in this state no very great affinity for the
sulphuric acid, parts with the greater portion of it to the clay, which
is thus converted into sulphate of alumina. Many of these schists are
of such a loose texture, and contain the pyrites in so fine a state
of division, that the requisite heat is generated by the rapidity
with which the several chemical changes proceed; others, from their
compactness and deficiency in combustible matter, require calcining
by a slow smothered fire. When the calcination is complete, the mass
is lixiviated, the solutions are run into cisterns for evaporation,
and when they have attained a certain strength, are precipitated with
sulphate or muriate of potash or ammonia. The precipitated alum is
washed, drained, and separated from various impurities by re-solution
and crytallization, and is then fit for the market.
A very interesting process has recently been patented by Dr. Turner of
Gateshead[543]. It consists in fusing felspar, which is a silicate of
potash and alumina, with more potash. On treating the fused mass with
water, it is separated into two parts; the first, a solution containing
silicate of potash, from which the potash may be obtained by passing
through it a stream of carbonic acid gas, or by filtering it through a
bed of caustic lime; the second, an insoluble residue, consisting of a
silicate of alumina and potash. On digesting this with sulphuric acid,
the silica is separated and a solution of alum obtained.]