A L T A L U 643 cattle, and sheep; and the town contains some highly reputed ale breweries, besides paper manufactories and an iron foundry. The church, a fine old building, was the scene of a fierce conflict between the royalist and parlia mentary troops in 1643. Population in 1871, 4092. ALTON, a town in Madison county, Illinois, United States, stands on a high bluff on the left bank of the Mississippi, 21 miles above St Louis, and 3 above the mouth of the Missouri. It is a place of considerable importance, and carries on a thriving export trade in the produce of the surrounding country grain, hay, fruit, coal, and lime. It has an excellent wharf, and good means of communication by railway, the two great lines from Chicago and Indianopolis having their junction at Alton. The town contains a Roman Catholic cathedral, about ten other churches belonging to various sects, and several schools. It has also a printing trade, with daily and weekly newspapers. Population in 1870, 8665. ALTONA, the richest and most populous city of the Prussian province of Schleswig-Holstein, is situated on the north bank of the Elbe, so close to Hamburg that the two cities are virtually one. The rise of Altona to its present position has been rapid, at least for a continental city, and is mainly due to the fostering care of the Danish govern ment, who established it as a rival to Hamburg. In 1640, when it became the property of Denmark, it was a small fishing village; in 1871 it contained 74,131 inhabitants. After the war of 1864 it ceased to belong to Denmark, and eventually became part of Prussia, although, with Hamburg, it is not included in the Zollverein. It carries on a large trade with Britain, France, the West Indies, and other countries; but it has by no means succeeded in depriving Hamburg of its commercial pre-eminence great part of the business of Altona being, indeed, transacted on the Hamburg exchange. Tobacco is probably the chief manufacture, but there are also breweries, tanneries, oil- works, soap-works, and linen factories. Altona is a well- built modern town, really dating from 1713 (when the Swedes burnt it to the ground), with a higher situation than that of Hamburg, and consequently a purer and healthier atmosphere. It contains an observatory of some celebrity, several churches, two synagogues, a gymnasium, and an infirmary. It is the terminus of the Altona-Kiel Railway, which places it in connection with the principal towns of Schleswig-Holstein. ALTO ON A, a town of the United States, in Blair county, Pennsylvania, on the Central Railway, 244 miles west of Philadelphia, situated near the eastern base of the Alle- ghany Mountain, where the railroad begins to ascend it. It contains extensive locomotive and railway carriage manu factories belonging to the Pennsylvania Central Railway Company. Near Altoona is the famous " Horse Shoe Bend," where trains of but ordinary length are seen to be moving in opposite directions at the same time. The line of railway, in its ascent between Altoona and Cresson, winds round the side of the mountain, affording some of the finest mountain scenery on the continent. Population in 1870, 10,610. ALTO-RILIEVO (high relief] is the term applied to sculpture that projects from the plane to which it is attached to the extent of more than one-half the outline of the principal figures. It is thus distinguished from basso-rilievo, in which there is a greater or less approximation to the pictorial method, the figures being made to appear as pro jecting more than half their outline without actually doing so. See RELIEF and SCULPTURE. ALTRINGHAM, or ALTRINCHAM, a market town in the north of Cheshire, 8 miles south of Manchester, with which it is connected by railway. It is a neat, clean place, surrounded by villas of Manchester manufacturers, who are attracted by its healthy climate and pleasant situation. It has no parish church, but there is a chapel of ease belonging to the parish of Bowdon, in which it is situated, and also a Roman Catholic and several dissenting places of worship. Yarn, worsted, and cotton are the chief manufactures; and large quantities of fruit and vegetables are sent to the Manchester market. Population in 1871, 8478. ALUM, a compound salt employed in dyeing and various other industrial processes. It is soluble in water, has an astringent, acid, and sweetish taste; reddens vege table blues, and crystallises in regular octahedrons. When heated, it liquefies; and if the heat be continued, the water of crystallisation is driven off, the salt frothes and swells, and at last a white matter remains, known by the name of burnt alum. Its constituents are sulphuric acid, alumina, an alkali, and water. The alkali may be either potash, soda, or ammonia. Hence there are three distinct species of alum, depending upon the nature of the alkali which each con tains. Potash alum (in which the alkali is potash) is the common alum of this country, although both soda alum, and ammoniacal alum are manufactured. The term alum is now used in chemistry as a generic one, and is applied to the class of double salts formed by the union of the sulphates of alumina, chromium, or iron with the sulphates of the alkalies. The composition of the ordinary potash alum is represented by the formula A1K(S0 4 ) 2 - 12H 3 0. The progress made by chemists in the discovery of the constitution of alum was very slow. The species first investigated was potash alum. That it contained sulphuric acid as a constituent was known even to the alchemists. Pott and Marggraff demonstrated that alumina was another constituent. Pott, in his Lithogeognosia, showed that the earth of alum, or the precipitate obtained when an alkali is poured into a solution of alum, is quite different from lime and chalk, with which it had been confounded by Stahl. Marggraff went much farther. He not only showed that alumina is one of the constituents of alum, but that this earth possesses peculiar properties, is different from every other substance, and is one of the ingredients in common clay (" Experiences faites sur la Terre d Alun," Marggraff s Opusc. ii. 111). Marggraff showed likewise, by many experiments, that crystals of alum cannot be obtained by dissolving alumina in sulphuric acid, and evaporating the solutions. The crystals formed are always soft, and quite different in their appearance from aluin crystals. But when a solution of potash or ammonia is dropt into this liquid, it immediately deposits perfect crystals of alum (" Sur la Reg6n6ration de 1 Alun," Marg graff s Opusc. ii. 86). He mentions likewise that manu facturers of alum in general were unable to procure the salt without a similar addition, that at first it had beer customary to add a quantity of putrid urine, and thai afterwards a solution of carbonate of potash was sub stituted in its place. But siibscquent chemists do not seem to have paid much attention to these important observations of Marggraff: they still continued, without any rigid examination, to consider alum as a sulphate of alumina. Bergmann indeed had observed that the addition of potash or ammonia made the alum crystallise, but that the same effect was not produced by the addition of soda or of lime ("De Confectione Aluminis/ Bergmann s Opusc. i. 225). He had observed likewise that sulphate of potash is fre quently found in alum. He decomposed the solution of alum by means of ammonia, evaporated the filtered liquid to dryness, and exposed the residue to a red heat. A quantity of sulphate of potash often remained behind in
the crucible (ibid., p. 326). From these facts he drew
