the bottom of the caldron. The caldron, being thus prepared, is entirely
filled through a launder with water, and this is boiled with a fierce fire
until it bubbles. Then little by little eight wheelbarrow loads of the
material, composed of roasted rock moistened with water, are gradually
emptied into the caldron by four workmen, who, with their shovels which
reach to the bottom, keep the material stirred and mixed with water, and
by the same means they lift the lumps of undissolved rock out of the
caldron. In this manner the material is thrown in, in three or four lots, at
intervals of two or three hours more or less ; during these intervals, the
water, 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 and
run 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, and
four feet wide. In these the water congeals and condenses into alum, in the
spring in the space of four days, and in summer in six days. Afterward the
holes at the bottom of the oak troughs being opened, the water which has
not 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 water
which is not altogether wanting in alum, is considered better than that which
has none at all. Then the alum is hewn out with a knife or a chisel. It is
thick and excellent according to the strength of the rock, either white or
pink according to the colour of the rock. The earthy powder, which remains
three to four digits thick as the residue of the alum at the bottom of the
trough is again thrown into the caldron and boiled with fresh aluminous
material. 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 of
Pope Pius η. (1614, p. 185), it appears that this Italian had been engaged in
dyeing cloth in Constantinople, and thus became aware of the methods of making
alum. Driven out of that city through its capture by the Turks, he returned to Italy and
obtained an office under the Apostolic Chamber. While in this occupation he discovered a
rock at Tolfa which appeared to him identical with that used at Constantinople in alum
manufacture. After experimental work, he sought the aid of the Pope, which he obtained
after much vicissitude. Experts were sent, who after examination " shed tears of joy, they
kneeling down three times, worshipped God and praised His kindness in conferring such a gift
on their age." Castro was rewarded, and the great papal monopoly was gradually built upon
this discovery. The industry firmly established at Tolfa exists to the present day, and is the
source 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 had
greater complaint than against the Turks. The history of the disputes arising over the
papal alum monopoly would alone fill a volume.
By the middle of the 15th Century alum was being made in Spain, Holland, and
Germany, and later in England. In her efforts to encourage home industries and escape the
tribute to the Pope, Elizabeth (see Note on p. 283) invited over " certain foreign chvmistes and
mineral masters " and gave them special grants to induce them to " seme in these
realmes." Among them was Cornelius Devoz, to whom was granted the privilege of " mining
and digging in our Realm of England for allom and copperas." What Devoz accomplished
is not recorded, but the first alum manufacture on a considerable scale seems to have been in
Yorkshire, by one Thomas Chaloner (about 1608), who was supposed to have seduced
workmen from the Pope's alum works at Tolfa, for which he was duly cursed with all the
weight of the Pope and Church. (Pennant, Tour of Scotland, 1786).
