Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/685

Rh A L U A L V 647 eeem to be partly impregnated with sulphate of iron. They are dissolved in hot water, and the solution poured into troughs, and allowed to crystallise a second time. These second crystals, though much purer, are not quite free from sulphate of iron ; but the separation is accom plished by washing them repeatedly with cold water ; for sulphate of iron is much more soluble in that liquid than alum. These second crystals are now dissolved in as small a quantity of hot water as possible, and the concentrated liquid poured while hot into large casks, the surface of which is covered with two cross beams. As the liquor cools, a vast number of alum crystals form on the sides and surface. The casks are allowed to remain till the liquid within is supposed to be nearly of the temperature of the atmosphere. This, in winter, requires eleven days ; in summer, fourteen or more. The liquid, after standing eleven days in summer, has been observed to be still above blood heat. The hoops are then removed, precisely as in the manufacture of alum from alum-slate. There always remains in the boilers a yellowish sub stance, consisting chiefly of peroxide of iron. This is exposed to a strong heat in a reverberatory furnace, and it becomes red. In this state it is washed, and yields more alum. The red residue is ground to a fine powder, and dried. It then answers all the purposes of Venetian red as a pigment. By altering the temperature to which this matter is exposed, a yellow ochre is obtained instead of a red. In France, where alum ores are by no means abundant, alum is manufactured from clay. This method of making the salt was first put in practice by Chaptal when pro fessor of chemistry at Montpellier. His methods have been since gradually improved, and brought to a state of considerable perfection. The first process tried was this : The clay was reduced to a fine powder in a mill, and then mixed with sulphuric acid. After remaining some days, it was exposed for twenty-four hours to a temperature of about 130. It was then lixiviated, and the liquid mixed with urine or potash. This method being found incon venient, was abandoned for the following: The clay being well ground, was mixed with half its weight of the saline residue from a mixture of sulphur and nitre. This residue is little else than sulphate of potash. The mixture was formed into balls about 5 inches in diameter, which were calcined in a potter s furnace. They were then placed on the floor of a chamber in which sulphuric acid was made. The acid vapour caused them to swell, and to open on all sides. In about a month they were sufficiently penetrated with the acid. They were then exposed to the air, under shades, that the saturation might become more complete. Finally, they were lixiviated, and the liquid being evapo rated, yielded pure alum. This process was considerably improved by Berard, of the Montpellier alum work. Instead of exposing the calcined balls to the fumes of sulphuric acid, he sprinkled them with a quantity of sulphuric acid of the specific gravity 1 367, equal to the weight of the clay employed; but it is obvious that the proportion must vary with the nature of the clay. The solution takes place with the greatest facility, and crystals of alum are obtained by evaporating the liquid. Another process was put in practice by Chaptal, in the neighbourhood of Paris. A mixture is made of 100 parts of clay, 50 parts of nitre, and 50 parts of sulphuric acid of the specific gravity 1 367 ; and this mixture is put into a retort and distilled. Aquafortis comes over, and the residue in the retort being lixiviated with water, yields abundance of excellent alum. For chemical constitution and relations of the alums, eee CHEMISTRY. ALUMBAGH, the name of a large park or walled enclosure, containing a palace, a mosque, and other build ings, as well as a beautiful garden, situated about 4 miles from Lucknow, near the Cawnpore road. It was converted into a fort by the mutineers in 1857; and after its capture by the British was of importance in connection with the military operations around Lucknow. See LUCKNOW. ALUMINIUM, a metallic substance, first separated from the chloride by Wohler in 1828. It remained a laboratory product until Deville, about 1858, succeeded in improving the mode of production, so as to render the operations capable of management on the manufacturing scale. Tho process consists in heating to a red heat a mixture of the double chloride of aluminium and sodium, or the double fluoride of aluminium and sodium (cryolite), with the metal sodium. A vigorous action takes place, chloride of sodium being formed and the metal aluminium separated. On the large scale the reduction is effected by throwing a mixture of 10 parts of the double chloride, 5 parts of cryolite, and 2 parts of sodium on the hearth of a reverberatory furnace. Immediately after the action, the fused metal and slag, consisting of common salt and fluoride of aluminium, are run out, and a new quantity of the previous mixture intro duced. The various patents that have been secured with reference to this manufacture have all regard to the saving of the metal sodium. The metal aluminium may be separated from the double chloride by electrolysis. For this purpose the fused salt has the electric current from ten cells of a battery passed through it, carbon poles being used. The metal appears at the negative pole in large globules, which may be collected and melted together under a layer of fused salt. Aluminium is a white metal resembling silver in appear ance. It is very malleable and ductile, and may be beaten and rolled into thin sheets, or drawn into fine wire. By hammering in the cold it becomes as hard as soft iron, but may be softened again by fusion. Being highly sonorous, it has been used for making bells. It is veiy light, being only 2 times heavier than water, and is thus four times lighter than silver. After fusion it has a specific gravity of 2 &quot;56; by hammering this may be increased to 2 67. It melts at a red heat, and is n on- volatile at very high temperatures. The metal conducts heat and electricity as well as silver. Aluminium does not oxidise in air, even at a red heat, has no action on water at ordinary tempera tures, and is not acted upon by sulphuretted hydrogen or sulphide of ammonium, and thus preserves its lustre where silver would be tarnished and blackened. It is not at tacked by nitric acid, even when concentrated, and is not soluble in dilute sulphuric acid, but is readily soluble in dilute or concentrated hydrochloric acid with evolution of hydrogen. Solutions of caustic potash or soda dissolve the metal with great ease, forming aluminate of potash or soda, and giving off hydrogen. Aluminium forms alloys with most metals. The copper alloy called aluminium- bronze is the most important because of its colour, hard ness, and malleability, and is largely used for articles of jewellery, for mounting sextants and other astronomical instruments, and for making balance beams. ALUTA, an affluent of the Danube. See ALT. ALVA, a village in Stirlingshire, Scotland, situated at the foot of Craigleith, one of the Ochil range, 7 miles N.E. of Stirling, with which it is connected by railway. Besides the parish church, there are places of worship belonging to the Free and United Presbyterian churches. Yarn spin ning and the manufacture of shawls and tweeds are carried on to a considerable extent. Population in 1871, 4096. ALVA, or ALBA, FERNANDO ALVAREZ DE TOLEDO, Duke of, born in 1508, was descended from one of the most illustrious families in Spain. His grandfather, Ferdinand