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BOOK XII.

the vessels and vats is again poured back into the caldron to be re-boiled.The earth which settled at the bottom of the caldron is carried back to thetanks, and, together with the ore, is again dissolved with water and urine.The earth which remains in the tanks after the solution has been drawn offis emptied in a heap, and daily becomes more and more aluminous in thesame way as the earth from which saltpetre was made, but fuller of its juices,wherefore it is again thrown into the tanks and percolated by water.

Aluminous rock is first roasted in a furnace similar to a lime kiln. Atthe bottom of the kiln a vaulted fireplace is made of the same kind of rock;the remainder of the empty part of the kiln is then entirely filled with thesame aluminous rocks. Then they are heated with fire until they are redhot and have exhaled their sulphurous fumes, which occurs, according to theirdivers nature, within the space of ten, eleven, twelve, or more hours. Onething the master must guard against most of all is not to roast the rockeither too much or too little, for on the one hand they would not soften whensprinkled with water, and on the other they either would be too hard orwould crumble into ashes ; from neither would much alum be obtained, forthe strength which they have would be decreased. When the rocks are cooledthey are drawn out and conveyed into an open space, where they are piled oneupon the other in heaps fifty feet long, eight feet wide, and four feet high,which are sprinkled for forty days with water carried in deep ladles. Inspring the sprinkling is done both morning and evening, and in summer at

“rubbed, it should be without roughness, and should give a little heat. This is called“ phorimon. The mode of detecting whether it has been adulterated is by pomegranate“juice, for, if genuine, the mixture turns black. The other, or solid, is pale and rough“ and turns dark with nut-galls ; for which reason it is called paraphoron. Liquid alumen is“ naturally astringent, indurative, and corrosive ; used in combination with honey, it heals“ ulcerations. . . . There is one kind of solid alumen, called by the Greeks schistos,

‘ ‘ which splits into filaments of a whitish colour ; for which reason some prefer calling it“ trichitis (hair like). Alumen is produced from the stone chalcitis, from which copper is also"made, being a sort of coagulated scum from that stone. This kind of alumen is less" astringent than the others, and is less useful as a check upon bad humours of the body. . .

" The mode of preparing it is to cook it in a pan until it has ceased being a liquid. There“ is another variety of alumen also, of a less active nature, called strongyle. It is of two kinds.“ The fungous, which easily dissolves, is utterly condemned. The better kind is the pumice-" like kind, full of small holes like a sponge, and is in round pieces, more nearly white in colour," somewhat greasy, free from grit, friable, and does not stain black. This last kind is cooked" by itself upon charcoal until it is reduced to pure ashes. The best kind of all is that called“ melinum, from the Isle of Melos, as I have said, none being more effectual as an astringent,"for staining black, and for indurating, and none becomes more dry. . . . Above all other" properties of alumen is its remarkable astringency, whence its Greek name. . . . It is

“injected for dysentry and employed as a gargle.” The lines omitted refer entirely tomedical matters which have no bearing here. The following paragraph (often overlooked)from Pliny (xxxv., 42) also has an important bearing upon the subject:—“ In Egypt they" employ a wonderful method of dyeing. The white cloth, after it is pressed, is stained“ in various places, not with dye stuffs, but with substances which absorb colours. These“ applications are not apparent on the cloth, but when it is immersed in a caldron of hot“ dye it is removed the next moment brightly coloured. The remarkable circumstance“ is that although there be only one dye in the caldron yet different colours appear in the" cloth.”

It is obvious from Pliny’s description above, and also from the making of vitriol (seeNote 11, p. 572), that this substance was obtained from liquor resulting from natural orartificial lixiviation of rocks—in the case of vitriols undoubtedly the result of decompositionof pyritiferous rocks (such as chalcitis). Such liquors are bound to contain aluminumsulphate if there is any earth or clay about, and whether they contained alum would be aquestion of an alkali being present. If no alkali were present in this liquor, vitriol would