noon besides. After being moistened for this length of time the rocks begin
to fall to pieces like slaked lime, and there originates a certain new material
of the future alum, which is soft and similar to the liquidae medullae found
in the rocks. It is white if the stone was white before it was roasted, and
rose-coloured if red was mixed with the white; from the former, white
alum is obtained, and from the latter, rose-coloured. A round furnace is
made, the lower part of which, in order to be able to endure the force of
the heat, is made of rock that neither melts nor crumbles to powder by the
fire. It is constructed in the form of a basket, the walls of which are two
feet high, made of the same rock. On these walls rests a large round caldron
made of copper plates, which is concave at the bottom, where it is eight feet
in diameter. In the empty space under the bottom they place the wood to be
kindled with fire. Around the edge of the bottom of the caldron, rock
is built in cone-shaped, and the diameter of the bottom of the rock structure
is seven feet, and of the top ten feet ; it is eight feet deep. The inside,
after being rubbed over with oil, is covered with cement, so that it may be
able to hold boiling water ; the cement is composed of fresh lime, of
which the lumps are slaked with wine, of iron-scales, and of sea-snails,
ground and mixed with the white of eggs and oil. The edges of the caldron
are surmounted with a circle of wood a foot thick and half a foot high,
on which the workmen rest the wooden shovels with which they cleanse
the water of earth and of the undissolved lumps of rock that remain at
crystallize out first, and subsequent condensation would yield aluminum sulphate. If
alkali were present, the alum would crystallize out either before or with the vitriol. Pliny's
remark, "that portion of it which first matures is whitest", agrees well enough with this
hypothesis. No one will doubt that some of the properties mentioned above belong peculiarly
to vitriol, but equally convincing are properties and uses that belong to alum alone. The
strongly astringent taste, white colour, and injection for dysentry, are more peculiar to alum than
to vitriol. But above all other properties is that displayed in dyeing, for certainly if we read
this last quotation from Pliny in conjunction with the statement that white alumen produces
bright colours and the dark kind, sombe colours, we have the exact reactions of alum and
vitriol when used as mordants. Therefore, our view is that the ancient salt of this character
was a more or less impure mixture ranging from alum to vitriol—" the whiter the better."
Further, considering the ancient knowledge of soda (nitrum), and the habit of mixing it
into almost everything, it does not require much flight of imagination to conceive its admixture to the " water," and the absolute production of alum.
Whatever may have been the confusion between alum and vitriol among the Ancients,
it appears that by the time of the works attributed to Geber (12th. or 13th Century), the
difference was well known. His work (Investigationes perfectiones, iv.) refers to alumen
glaciale and alumen jameni as distinguished from vitriol, and gives characteristic reactions
which can leave no doubt as to the distinction. We may remark here that the repeated statement apparently arising from Meyer (History of Chemistry, p. 51) that Geber used the term
alum de rocca is untrue, this term not appearing in the early Latin translations. During
the 15th Century alum did come to be known in Europe as alum de rocca. Various attempts have
been made to explain the origin of this term, ranging from the Italian root, a " rock, " to the
town of Rocca in Syria, where alum was supposed to have been produced. In any event,
the supply for a long period prior to the middle of the 15th Century came from Turkey, and
the origin of the methods of manufacture described by Agricola, and used down to the
present day, must have come from the Orient.
In the early part of the 15th Century, a large trade in alum was done between Italy
and Asia Minor, and eventually various Italians established themselves near Constantinople
and Smyrna for its manufacture (Dudae, Historia Byzantina Venetia, 172g, p. 71).
The alum was secured by burning the rock, and Iixiviation. With the capture of Constantinople by the Turks (1453), great feeling grew up in Italy over the necessity of buying this
requisite for their dyeing establishments from the infidel, and considerable exertion was
made to find other sources of supply. Some minor works were attempted, but nothing much
