A History of Inventions, Discoveries, and Origins. Johann Beckmann

Чтение книги онлайн.

СКАЧАТЬ 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.

502 Noct. Att. lib. xv. c. 1.

503 The halotrichum of Scopoli. The first person who discovered this salt to be vitriolic was Henkel, who calls it Atlas-vitriol. [The mineral halotrichite is, in a chemical sense, a true alum in which the sulphate of potash is replaced by the sulphate of the protoxide of iron. It is composed of one atom of protosulphate of iron, one atom of sulphate of alumina, and contains, like all the true alums, twenty-four atoms of water.]

504 Wecker De Secretis, lib. ix. 18, p. 445.

505 One instance of its being used for this purpose is found in Ammianus Marcellinus, lib. xx. c. 12.

506 [This cannot be correct; for Geber, who is supposed to have lived in the eighth century, was acquainted with three kinds of it, and describes the method of preparing burnt alum.]

507 Joh. Serapionis Arabis de simplicibus medicinis opus, cap. 410.

508 Reisebeschreibung, ii. p. 408, 409.

509 This singular appellation occurs in Valentini Historia Simplicium, and several other works.

510 Jul. Cæs. Scaligeri Exot. exercitat. Franc. 1612, 8vo, p. 325.

511 СКАЧАТЬ