ALUM 105 



powder ; and this again, when treated with potash, evolves ammonia, and assumes a 

 violet-blue colour. This solution of aloetic acid in ammonia is violet. 



AXiPACA. (Alpaga, Fr.) An animal of Peru, of the Llama species ; also the 

 name given to a woollen fabric woven from the wool of this animal, or a mixture of 

 silky goat's hair with the harsher fibre of sheep's wool. See LLAMA. 



AXiSTONTTE. A double carbonate of lime and baryta, crystallising in the 

 prismatic or orthorhombic system. It occurs at Fallowfiold, near Hoxham, in 

 Northumberland ; and at Bromley Hill, near Alston, in Cumberland. 



AXiirDEXi. The aludels of the earlier chemists were a series of pear-shaped pots, 

 generally made of earthenware, but sometimes of glass, open at both ends. Each 

 aludel had a short neck at top and bottom, so that a series of them could be fitted 

 together, by means of the neck, in succession. The earthenware pear-shaped vessels 

 in which the mercurial vapours are condensed, at Almaden, in Spain, are also known 

 as aludels. See MERCURY. 



AIiTTlVT. (Alun, Fr.; Alaun, Ger.) A saline body or salt, consisting of alumina, 

 or the peculiar earth of clay, united with sulphuric acid, and these again united 

 with sulphate of potash or of ammonia. In other words, it is a double salt, con- 

 sisting of sulphate of alumina and sulphate of potash, or sulphate of alumina and 

 sulphate of ammonia. The common alum crystallises in octahedrons, but there is a 

 kind which takes the form of cubes. It has a sour or rather subacid taste, and is 

 peculiarly astringent. It reddens the blue colour of litmus or red cabbage, and acts 

 like an acid on many substances. Other alkalis may take the place of the ammonia 

 or potash, and other metals that of the aluminium. 



Alum was known to the ancients, who used it in medicine, as it is now used, and 

 also as a mordant in dyeing and calico-printing, as at the present day. Old historians 

 do not describe correctly, either the mode of obtaining it or its exact characteristics, 

 so that it is confounded with sulphate of iron, with which it seems generally to have 

 been mixed. But that some qualities were made with very little iron in it, is clear 

 from the fact that it was employed when white for dyeing bright colours. (Pliny, 

 xxxv. 15.) It is said by Pliny that the purchasers tested it with tannin (pomegranate 

 juice), in order to see if it blackened. He says that the white kind blackened as well 

 as the black ; but in all probability this was a test applied by the dyers to see which 

 blackened least, so as to obtain, a good mordant for reds. Pliny's description, 

 although confused, leaves this fact perfectly clear that there woro men in whose 

 minds the knowledge was much clearer than in his, or a manufacture of such magni- 

 tude could not have existed. There is mention of some being made from stone, and 

 crystallising in fine hairs, but the characteristics given do not enable us to decide 

 that this was either alum or the peculiar sulphate of alumina which takes that form. 

 The alum was sometimes boiled down to dryness, and heated till it was spongy or 

 like pumice-stone. It was used as burnt alum. 



The ancients used it also for preventing the combustibility of wood and wooden 

 buildings. But although the knowledge of it was very accurate, their writers always 

 imagine that sulphate of iron was a kind of alum, because it is said that the black alum 

 was used for dyeing dark colours. They used iron as a mordant, and found its character 

 by galls or by pomegranate juice, which contains tannin. Their alum was chiefly a 

 natural production, and they removed the fine efflorescing crystals which first 

 appeared, or which gradually are raised above the rest, as the finest kind. ' It was 

 produced in Spain, Egypt, Armenia, Macedonia, Pontus, and Africa; the islands 

 Sardinia, Melos, Lipari, and Stromboli. The best was got in Egypt, the next in 

 Melos." The word is probably Egyptian, as it was best and most abundantly 

 obtained in Egypt. It is not probable that it was the double salt in all cases, but 

 simply a sulphate of alumina. Pliny, indeed, says that a substance called in Greek 

 vypa, or watery, probably from its very soluble nature, and which was milk-white, 

 was used for dyeing wool of bright colours. This may have been the mountain 

 butter of the German mineralogists, which is a native sulphate of alumina, iron, &c., of a 

 soft texture, waxy lustre, and unctuous to the touch. The stypteria of Dioscorides 

 and the alumen of Pliny -comprehended, no doubt, a variety of saline substances 

 besides sulphate of iron and alum. 



It seems to have come to Europe in later times as alum of Pocca, the name of 

 Edessa, or that place where the Italians first learnt the art ; but it is not impossible 

 that this name was an Italian prefix, which has remained to this day under the form 

 of Bock alum, Allume di rocca. The East has always had some manufactures 

 of it, and Phocis, Lesbos, and other places, were able to supply the Turks with 

 alum for their magnificent Turkey red. It was also made at Foya Nova, near 

 Smyrna, and at Constantinople. The Genoese and other trading people of Italy 

 imported alum into Western Europe for tho use of the dyers of red cloth. 



A Genoese merchant, Bartholomew Perdix, who had been in Syria, observed a 



