Online Encyclopedia

commerce, although both soda alum and ammonium alum are manufactured. The presence of sulphuric acid in potash alum was known to the alchemists. J. H. See also:

Pott and A. S. See also:

MARGGRAF, ANDREAS SIGISMUND (1709-1782)

Marggraf demonstrated that alumina was another constituent. Pott in his Lithogeognosia showed that the precipitate obtained when an alkali is poured into a See also:

SOLUTION (from Lat. solvere, to loosen, dissolve)

solution of alum is quite different from See also:

lime and See also:

CHALK

chalk, with which it had been confounded by G.

E. See also:

Stahl. Marggraf showed that alumina is one of the constituents of alum, but that this See also:

earth possesses See also:

PECULIAR

peculiar properties, and is one of the ingredients in common See also:

clay (Experiences faites sur la terre de l'alun, Marggraf's Opusc. ii.111). He also showed that crystals of alum cannot be obtained by dissolving alumina in sulphuric acid and evaporating the solutions, but when a solution of potash or See also:

AMMONIA (NH3)

ammonia is dropped into this liquid, it immediately deposits perfect crystals of alum (Sur la regeneration de l'alun, Marggraf's Opusc. ii. 86). T. 0. See also:

BERGMAN, TORBERN OLOF (1735-1784)

Bergman also observed that the addition of potash or ammonia made the solution of alumina in sulphuric acid crystallize, but that the same effect was not produced by the addition of soda or of lime (De confectione aluminus, Bergman's Opusc. i. 225), and that potassium sulphate is frequently found in alum. After M. H. See also:

Klaproth had discovered the presence of potassium in See also:

LEUCITE

leucite and See also:

LEPIDOLITE

lepidolite, it occurred to Li N.

See also:

VAUQUELIN, LOUIS NICOLAS (1763-1829)

Vauquelin that it was probably an ingredient likewise in many other minerals. Knowing that alum cannot be obtained in crystals without the addition of potash, he began to suspect that this alkali constituted an essential ingredient in the salt, and in 1797 he published a dissertation demonstrating that alum is a double salt, composed of sulphuric acid, alumina and potash (Annales de chimie, xxii. 258). Soon after, J. A. See also:

CHAPTAL, JEAN ANTOINE CLAUDE, COMTE DE

Chaptal published the See also:

ANALYSIS (Gr. avci and Meta, to break up into parts)

analysis of four different kinds of alum, namely, See also:

ROMAN

Roman alum, See also:

LEVANT

Levant alum, See also:

BRITISH

British alum and alum manufactured by himself. This analysis led to the same result as that of Vauquelin (See also:

Ann. de chim. xxii. 280). The word alumen, which we translate alum, occurs in See also:

Pliny's Natural See also:

HISTORY

History. In the 15th See also:

CHAPTER (a shortened form of chapiter, a word still used in architecture for a capital; derived from O. Fr. chapitre, Lat. capitellum, diminutive of caput, head)

chapter of his 35th See also:

BOOK

book he gives a detailed description of it. By comparing this with the See also:

account of vrrvnrrrtpia given by Dioscorides in the 123rd chapter of his 5th book, it is obvious that the two are identical. Pliny informs us that alumen was found naturally in the earth.

He calls it salsugoterrae. Different substances were distinguished by the name of alumen"; but they were all characterized by a certain degree of astringency, and were all employed in dyeing and See also:

MEDICINE

medicine, the See also:

LIGHT

light-coloured alumen being useful in brilliant dyes, the dark-coloured only in dyeing See also:

black or very dark See also:

COLOURS, MILITARY

colours. One See also:

SPECIES

species was a liquid, which was See also:

apt to be adulterated; but when pure it had the See also:

PROPERTY

property of blackening when added to See also:

POMEGRANATE

pomegranate juice. This property seems to characterize a solution of iron sulphate in water; a solution of See also:

ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary (potash) alum would possess no such property. Pliny says that there is another See also:

KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind of alum which the Greeks See also:

CALL (from Anglo-Saxon ceallian, a common Teutonic word, cf. Dutch kallen, to talk or chatter)

call schistos. It forms in See also:

white threads upon the See also:

SURFACE

surface of certain stones. From the name schistos, and the mode of formation, there can be little doubt that this species was the salt which forms spontaneously on certain slaty minerals, as alum See also:

SLATE (properly CLAY SLATE; in M. Eng. slat or sclat, from O. Fr. esclat, a small piece of wood used as a tile; esclater, to break into pieces, whence modern Fr. eclat, the root being seen also in Ger. schleissen, to split)

slate and bituminous shale, and which consists chiefly of the sulphates of iron and aluminium. Possibly in certain places the iron sulphate may have been nearly wanting, and then the salt would be white; and would See also:

ANSWER (derived from and, against, and the same root as swear)

answer, as Pliny says it did, for dyeing See also:

bright colours. Several other species of alumen are described by Pliny, but we are unable to make out to what minerals he alludes. The alumen of the ancients, then, was not the same with the alum of the moderns. It was most commonly an iron sulphate, sometimes probably an aluminium sulphate, and usually a mixture of the two. But the ancients were unacquainted with our alum.

They were acquainted with a crystallized iron sulphate, and distinguished it by the names of misy, sory, chalcanthum (Pliny xxxiv. 12). As alum and See also:

green See also:

VITRIOL

vitriol were applied to a variety of substances in common, and as both are distinguished by a sweetish and astringent taste, writers, even after the See also:

DISCOVERY

discovery of alum, do not seem to have discriminated the two salts accurately from each other. In the ;writings of the alchemists we find the words misy, sory, chalcanthum applied to alum as well as to iron sulphate; and the name at; amentum sutorium, which ought to belong, one would suppose, exclusively to green vitriol, applied indifferently to both. Various minerals are employed in the manufacture of alum, the most important being See also:

ALUNITE, or ALUMSTONE

alunite (q.v.) or alum-See also:

stone, alum schist, See also:

BAUXITE

bauxite and See also:

CRYOLITE

cryolite. In See also:

order to obtain alum from alunite, it is calcined and then exposed to the See also:

ACTION

action of See also:

air for a considerable See also:

time. During this exposure it is kept continually moistened with water, so that it ultimately falls to a very See also:

FINE

fine powder. This powder is then lixiviated with hot water, the liquor decanted, and the alum allowed to crystallize. The alum See also:

SCHISTS (Gr. vxq'ecv, to split)

schists employed in the manufacture of alum are mixtures of iron See also:

PYRITES

pyrites, aluminium silicate and various bituminous substances, and are found in upper See also:

BAVARIA (Ger. Bayern)

Bavaria, Bohemia, See also:

Belgium and See also:

Scotland. These are either roasted or exposed to the weathering action of the air. In the roasting See also:

PROCESS

process, sulphuric acid is formed and acts on the clay to See also:

FORM (Lat. forma)

form aluminium sulphate, a similar See also:

CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition of affairs being produced during weathering. The See also:

mass is now systematically extracted with water, and a solution of aluminium sulphate of specific gravity 1.16 is prepared.

This solution is allowed to stand for some time (in order that any See also:

CALCIUM [symbol Ca, atomic weight 40.0 (o= x6)]

calcium sulphate and basic ferric sulphate may See also:

SEPARATE

separate), and is then evaporated until ferrous sulphate crystallizes on cooling; it is then See also:

DRAWN

drawn off and evaporated until it attains a specific gravity of 1.4o. It is now allowed to stand for some time, decanted from any sediment, and finally mixed with the calculated quantity of potassium sulphate (or if ammonium alum is required, with ammonium sulphate), well agitated, and the alum is thrown down as a finely-divided precipitate of alum See also:

MEAL

meal. If much iron should be See also:

PRESENT

present in the shale then it is preferable to use potassium chloride in See also:

PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place of potassium sulphate. In the preparation of alum from See also:

CLAYS, PAUL JEAN (1819-1900)

clays or from bauxite, the material is gently calcined, then mixed with sulphuric acid and heated gradually to boiling; it is allowed to stand for some time, the clear solution drawn off and mixed with acid potassium sulphate and allowed to crystallize. When cryolite is used for the preparation of alum, it is mixed with calcium carbonate and heated. By this means, sodium aluminate is formed; it is then extracted with water and precipitated either by sodium bicarbonate or by passing a current of See also:

CARBON (symbol C, atomic weight 12)

carbon dioxide through the solution. The precipitate is then dissolved in sulphuric acid, the requisite amount of potassium sulphate added and the solution allowed to crystallize. Potash alum, K2SO4•Al2(SO4)s.24H20, crystallizes in regularoctahedra and is very soluble in water. The solution reddens litmus and is an astringent. When heated to nearly a red See also:

HEAT (0. E. haktu, which like " hot," Old Eng. hat, is from the Teutonic type haita, hit, to be hot; cf. Ger. hitze, heiss; Dutch, hitte, heet, &c.)

heat it gives a porous friable mass which is known as " burnt alum." It fuses at 92° C. in its own water of crystallization. " Neutral alum " is obtained by the addition of as much sodium carbonate to a solution of alum as will begin to cause the separation of alumina; it is much used in mordanting. Alum finds application as a See also:

MORDANT

mordant, in the preparation of lakes for sizing See also:

hand-made See also:

paper and in the clarifying of turbid liquids.

Sodium alum, Na2SO4•Al2(SO4),.24H2O, occurs in nature as the See also:

MINERAL

mineral mendozite. It is very soluble in water, and is extremely difficult to purify. In the preparation of this salt, it is preferable to mix the component solutions in the See also:

COLD (in O. Eng. cald and ceald, a word coming ultimately from a root cognate with the Lat. gelu, gelidus, and common in the Teutonic languages, which usually have two distinct forms for the substantive and the adjective, cf. Ger. Kolte, kalt, Dutch koude

cold, and to evaporate them at a temperature not exceeding 6o° C. too parts of water dissolve See also:

ITO, HIROBUMI, PRINCE (1841-1909)

Ito parts of sodium alum at o° C. (W. A. See also:

TILDEN, SAMUEL JONES (1814-1886)

Tilden, Jour. Chem. See also:

Soc., 1884, 45, p. 409), and 51 parts at 16° C. (E. Auge, Comptes rendus, 189o, to, p. 1134).

Chrome alum, K2SO4•Cr2(SO4)3.24H20, appears chiefly as a by-product in the manufacture of See also:

ALIZARIN, or I

alizarin, and as a product of the reaction in bichromate batteries. The solubility of the various alums in water varies greatly, sodium alum being readily soluble in water, whilst caesium and rubidium alums are only sparingly soluble.

End of Article: ALUM

Additional information and Comments

There are no comments yet for this article.

» Add information or comments to this article.

Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML.

Site content, images, and layout Copyright © 2006 - Net Industries, worldwide.
Do not copy, download, transfer, or otherwise replicate the site content in whole or in part.

Links to articles and home page are always encouraged.

[back]
ALTWASSER

[next]
ALUMINIUM (symbol Al; atomic weight 27.0)