In England the first alum-work was erected at Gisborough in Yorkshire, in the reign of queen Elizabeth; though Anderson539 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 established540. 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 them541.
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 Andrarum542 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 Gateshead543. 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.]
FOOTNOTES
487 Called by the Greeks στυπτηρία.
488 [It is scarcely necessary to observe, that many of the compounds of sulphuric acid with metallic oxides were formerly commonly termed vitriols from their glassy appearance; thus, the green vitriol, or briefly vitriol, is the sulphate of the protoxide of iron, white vitriol is sulphate of zinc, and blue vitriol is the sulphate of copper. Sulphuric acid is still more generally known by the name of oil of vitriol and vitriolic acid, from its having been originally obtained by distilling green vitriol.]
489 [There can be little doubt however that even Pliny was acquainted with our alum, but did not distinguish it from sulphate of iron, for he informs us that one kind of alum was white and was used for dyeing wool of bright colours.—Pereira’s Materia Medica, vol. i.]
490 [The alums, for at present several kinds are distinguished, are not merely combinations of sulphuric acid and the earth alumina, but double sulphates, the one constituent being sulphate of alumina, the other either sulphate of potash, sulphate of ammonia, sulphate of soda, &c. The alum of this country generally contains potash, that of France ammonia, or both potash and ammonia, hence the name potash-alum, ammonia-alum, &c.]
491 [Although native alum is not abundant, there is no question of its occasional occurrence.]
492 Plin. lib. xxxiv. c. 12. The same account is given by Isidor. Origin. lib. xvi. c. 2, and by Dioscorides, lib. v. c. 114. The latter, however, differs from Pliny in many circumstances.
493 Those who are desirous of seeing everything that the ancients have left us respecting their alum may consult Aldrovandi Museum Metallicum, Lugd. 1636, fol. p. 334.
494 Herodot. lib. ii. c. 180.
495 Diodor. Sic. lib. v. ed. Wesselingii, i. p. 338.
496 Tournefort, Voyage i. p. 63. Some information respecting the same subject may be seen in that expensive but useful work, Voyage Pittoresque de la Grèce, i. p. 12.
497 Diodor. Sic. lib. c. Strabo, lib. vi. edit. Almel. p. 423.
498 Copious information respecting the Spanish alum-works may be found in Introduccion à la Historia Natural de Espagna, par D. G. Bowles: and in Dillon’s Travels through Spain, 1780, 4to, p. 220.
499 The derivation of the Latin name alumen, which, if I mistake not, occurs first in Columella and Pliny, is unknown. Some deduce it from ἅλμη; others from ἄλειμμα; and Isidore gives a derivation still more improbable. May it not have come from Egypt with the best sort of alum? Had it originated from a Greek word, it would undoubtedly have been formed from στυπτηρία. This appellation is to be found in Herodotus; and nothing is clearer than that it has arisen from the astringent quality peculiar to both the salts, and also from στύφειν, as has been remarked by Dioscorides, Pliny, and Galen.
500 Etymol. p. 779.
501 Plin. lib. xxxiv. c. 12.