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BOOK XII.

the bottom of the caldron. The caldron, being thus prepared, is entirelyfilled through a launder with water, and this is boiled with a fierce fireuntil it bubbles. Then little by little eight wheelbarrow loads of thematerial, composed of roasted rock moistened with water, are graduallyemptied into the caldron by four workmen, who, with their shovels whichreach to the bottom, keep the material stirred and mixed with water, andby the same means they lift the lumps of undissolved rock out of thecaldron. In this manner the material is thrown in, in three or four lots, atintervals of two or three hours more or less ; during these intervals, thewater, which has been cooled by the rock and material, again begins to boil.The water, when sufficiently purified and ready to congeal, is ladled out andrun off with launders into thirty troughs. These troughs are made of oak,holm oak, or Turkey oak ; their interior is six feet long, five feet deep, andfour feet wide. In these the water congeals and condenses into alum, in thespring in the space of four days, and in summer in six days. Afterward theholes at the bottom of the oak troughs being opened, the water which hasnot congealed is drawn off into buckets and poured back into the caldron ;or it may be preserved in empty troughs, so that the master of the workmen,having seen it, may order his helpers to pour it into the caldron, for the waterwhich is not altogether wanting in alum, is considered better than that whichhas none, at all. Then the alum is hewn out with a knife or a chisel. It isthick and excellent according to the strength of the rock, either white orpink according to the colour of the rock. The earthy powder, which remainsthree to four digits thick as the residue of the alum at the bottom of thetrough is again thrown into the caldron and boiled with fresh aluminousmaterial. Lastly, the alum cut out is washed, and dried, and sold.

Alum is also made from crude pyrites and other aluminous mixtures.It is first roasted in an enclosed area ; then, after being exposed for some

eventuated until the appearance of one John de Castro. From the Commentaries ofPope Pius ii. (1614, p. 185), it appears that this Italian had been engaged indyeing cloth in Constantinople, and thus became aware of the methods of makingalum. Driven out of that city through its capture by the Turks, he returned to Italy andobtained an office under the Apostolic Chamber. While in this occupation he discovered arock at Tolfa which appeared to him identical with that used at Constantinople in alummanufacture. After experimental work, he sought the aid of the Pope, which he obtainedafter much vicissitude. Experts were sent, who after examination “shed tears of joy, theykneeling down three times, worshipped God and praised His kindness in conferring such a gifton their age.” Castro was rewarded, and the great papal monopoly was gradually built uponthis discovery. The industry firmly established at Tolfa exists to the present day, and is thesource of the Roman alum of commerce. The Pope maintained this monopoly strenuously,by fair means and by excommunication, gradually advancing the price until the consumers hadgreater complaint than against the Turks. The history of the disputes arising over thepapal alum monopoly would alone fill a volume.

By the middle of the 15th Century alum was being made in Spain, Holland, andGermany, and later in England. In her efforts to encourage home industries and escape thetribute to the Pope, Elizabeth (see Note on p. 283) invited over “ certain foreign chymistes andmineral masters ” and gave them special grants to induce them to “ settle in theserealmes.” Among them was Cornelius Devoz, to whom was granted the privilege of “ miningand digging in our Realm of England for allom and copperas.” What Devoz accomplishedis not recorded, but the first alum manufacture on a considerable scale seems to have been inYorkshire, by one Thomas Chaloner (about 1608), who was supposed to have seducedworkmen from the Pope’s alum works at Tolfa, for which he was duly cursed with all theweight of the Pope and Church. (Pennant, Tour of Scotland, 1786).