154 ALUM,

time that modern alum came into use; but it wasagain revived when it was discovered that alumcould be manufactured from aluminous mineralscontaining sulphur compounds. This circumstancehas served in some measure to strengthen the opinionthat the alum of the ancients and of the modems issynonymous, although the former was found andthe latter was extracted by a chemical process. Somehistorians of the fifteenth century speak of the alumworks as if the manufacture in Europe was only arevival.

Alum owes the high estimation in which it is heldto its value as a mordant in dyeing.

Alum works existed many centuries ago at Boha,or Koccha, in Mesopotamia , whence the old name ofItoch alum is applied to this salt. This is the opinionof Leibnitz , who states that alumen roccx was thatkind first procured from Bocca, and that the namewas subsequently given to every good species ofalum. A few are of opinion that alum obtainedfrom alum-stone has been so called to distinguish itfrom the alum from schists (schist was employed formaking alum in the time of Agricola), whichusually contains more iron than the former; andothers assert that alum acquired the name rocca fromthe aluminous rocks of Tolfa.

At a later date alum was manufactured nearSmyrna, and in the fifteenth century there werealum factories in the vicinity of Constantinople ,where John di Castro learned his art, as will behereafter noticed.

The inhabitants of Genoa , and other commercialpeople of Italy , imported alum from the above placesinto Western Europe for the use of dyers of redcloth. When these countries were taken by theTurks the Italians sought for and discovered alumin-ous minerals in their own soil, which caused theabandonment of many of the Turkish alum works.

Ddcas describes very minutely the alum works atFoya Nova, near Smyrna. Francis and Griffithstate that in Phocis, lying close to Ionia, there is amountain rich in aluminous mineral. The stonesfound at the summit are first calcined in the fire,and then reduced to powder by throwing them intowater. The moist mass is put into a kettle, a littlemore water added, and the whole having been madeto boil, the powder is lixiviated, the thick part whichfalls to the bottom in a cake is preserved, and thehard and earthy portions are discarded. The cake isafterwards allowed to dissolve in vessels for fourdays, at the end of which the alum is found in crys-tals around their edges, and their bottoms are alsocovered with the salt; the remaining liquor is pouredinto a kettle, diluted with water, and more powderadded, then boiled as before, and put into propervessels to crystallize. The alum obtained in thismanner is preserved as an article very necessary fordyers. Captains of ships bound from the Levant toEurope consider alum as a very convenient anduseful cargo for their vessels.

The alum works near Civita Yecchia are, by Italian historians, asserted to have been the first in Europe ;they are the oldest carried on at present. They

-History.

were founded by John di Castro, who learned theprocess near Constantinople . He was there tradingin Italian cloths and dyestuffs at the time the superbcity fell into the hands of the Turks; after this hereturned to his own country, and having found, inthe neighbourhood of Tolfa, a plant which he hadobserved growing abundantly in the aluminous dis-tricts of Asia , he conjectured that the virgin’soilmight also contain the same salt, and the astrln-gency of its taste proved he was correct. On thisdiscovery factories were immediately erected, theproduce of which was sold to the Venetians , theFlorentines, and the Genoese . The stones were firstcalcined, a large quantity of water was then thrownover them, and when they were entirely dissolvedthe lie was boiled in great leaden caldrons; afterwhich it was run into wooden vats and allowed tcevaporate spontaneously, the result being exceedinglygood alum. Pope Pius II . employed more than 800persons in preparing it. The plant which first inducedCastro to search for alum was the prickly evergreen,Ilex aquifolium, which in Italy is still considered asan indication that the regions where it thrives aboundwith alum. This shrub is, however, frequently foundgrowing where there is not the slightest trace of thissalt.

It appears, from all that can be learned, that theart of boiling alum was first understood in Italy , butnot previous to 1548. The great revenue which theApostolic Chamber derived from alum induced manyto seek aluminous minerals, and factories were builtwherever such w r ere found. Alum works soonappeared in Germany ; and in 1554 at Oberkau-fungen, in Hesse , a factory was in full operation.In 1566 letters patent were granted in England toCornelius de Vos, a Dutchman, for making “allomand copperas.” A bill passed the House of Commons confirming this grant, which it appeared De Vos hadassigned to Lord MouNtjoye. Nothing is known ofhis or Lord Mountjoye’s subsequent proceedings.Shortly after this date, however, an alum factory waserected at Gisborough, in Yorkshire , in the reign ofQueen Elizabeth, by Sir Thomas Chaloner , who,observing the trees tinged with an unusual colour,made him suspicious of its being owing to some mineralin the neighbourhood. He ascertained that the strataabounded with an aluminous salt. At that time theEnglish being strangers to the methods of managingit, there is a tradition that Sir Thomas was obligedto seduce some workmen from the Pope ’s alumworks, then the greatest in Europe .

Before entering minutely into the fabrication ofalum, it will be proper to state how and where thesalt is obtained. The greater portion of the alum inthis country is manufactured from alum shale, abituminous slaty clay containing iron bisulphide dif-fused in very fine particles throughout its mass ; ithas a bluish or greenish-black colour, and eliminatessulphurous acid when burned, acquiring thereby analuminous taste. Many of the alum slates crumbleto pieces, or suffer disintegration, on exposure tothe air; their sulphur becomes gradually convertedinto sulphuric acid by absorbing oxygen from the