BOOK XII. 569 



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 oU. 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 fordysentry, 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, sombre 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 admix- 

 ture 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 perfecHones, iv.) refers to alumen 

 glaciate 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 state- 

 ment 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, 1729, p. 71). 

 The alum was secured by burning the rock, and lixiviation. With the capture of Constan- 

 tinople 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 



