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566
BOOK XII.
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greater part of the water has evaporated. The earthy sediment deposited
at the bottom of the caldron is composed of fatty and aluminous matter, which usually consists of small incrustations, in which there is not infrequently found a very white and very light powder of asbestos or gypsum. The solution now seems to be full of meal. Some people instead pour the partly evaporated solution into a vat, so that it may become pure and clear ; then pouring it back into the caldron, they boil it again until it becomes mealy. By whichever process it has been condensed, it is then poured into a wooden tub sunk into the earth in order to cool it. When it becomes cold it is poured into vats, in which are arranged horizontal and vertical twigs, to which the alum clings when it condenses ; and thus are made the small white transparent cubes, which are laid to dry in hot rooms. If vitriol forms part of the aluminous ore, the material is dissolved in
water without being mixed with urine, but it is necessary to pour that into the clear and pure solution when it is to be.re-boiled. This separates the vitriol from the alum, for by this method the latter sinks to the bottom of the caldron, while the former floats on the top ; both must be poured separately into smaller vessels, and from these into vats to condense. If, however, when the solution was re-boiled they did not separate, then they must be poured from the smaller vessels into larger vessels and covered over ; then the vitriol separating from the alum, it condenses. Both are cut out and put to dry in the hot room, and are ready to be sold ; the solution which did not congeal in is now general. One of the strongest reasons put forward was that alum does not occur
native in appreciable quantities. Apart from the fact that the weight of this argument has been lost by the discovery that alum does occur in nature to some extent as an aftermath of volcanic action, and as an efflorescence from argillaceous rocks, we see no reason why the Ancients may not have prepared it artificially. One of the earliest mentions of such a substance is by Herodotus (n., 180) of a thousand talents of stypteria, sent by Amasis from Egypt as a contribution to the rebuilding of the temple of Delphi. Diodorus (v., i) mentions the abundance which was secured from the Lipari Islands (Stromboli, etc.), and a small quantity from the Isle of Melos. Dioscorides (v., 82) mentions Egypt, Lipari Islands, Melos, Sardinia, Armenia, etc., " and generally in any other places where one finds red ochre {rubrica)." Pliny (xxxv., 52) gives these same localities, and is more explicit as to how it originates—" from an earthy water which exudes from the earth." Of these localities, the Lipari Islands (Stromboli, etc.), and Melos are volcanic enough, and both Lipari and Melos are now known to produce natural alum (Dana. Syst. Min., p. 95 ; and Tournefort, " Relation d'un voyage du Levant," London, 1717, Lettre iv., Vol. 1.). Further, the hairlike alum of Dioscorides, repeated by Pliny below, was quite conceivably fibrous kalinite, native potash alum, which occurs commonly as an efflorescence. Be the question of native alum as it may—and vitriol is not much more common—our own view that the ancient alumen was alum, is equally based upon the artificial product. Before entering upon the subject, we consider it desirable to set out the properties of the ancient substance, a complete review of which is given by Pliny (xxxv., 52), he obviously quoting also from Dioscorides, which, therefore, we do not need to reproduce. Puny says :— " Not less important, or indeed dissimilar, are the uses made of alumen ; by which
" name is understood a sort of salty earth. Of this, there are several kinds. In Cyprus there "is a white alumen, and a darker kind. There is not a great difference in their colour, " though the uses made of them are very dissimilar,—the white alumen being employed in a " liquid state for dyeing wool bright colours, and the dark-coloured alumen, on the other " hand, for giving wool a sombre tint. Gold is purified with black alumen. Every kind of " alumen is from a limus water which exudes from the earth. The collection of it commences " in winter, and it is dried by the summer sun. That portion of it which first matures is the " whitest. It is obtained in Spain, Egypt, Armenia, Macedonia, Pontus, Africa, and the " islands of Sardinia, Melos, Lipari, and Strongyle ; the most esteemed, however, is that of *' Egypt, the next best from Melos. Of this last there are two kinds, the liquid alumen, and " the solid. Liquid alumen, to be good, should be of a limpid and milky appearance ; when |
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