180 AMMONIA.
to extract which it is pulverized and passed througha sieve. The fluoride may be used to prepare alu-minium.
Cryolite, i.e., aluminium ancl sodium fluoride (Al 2 E 6 ,6NaF), occurs in great abundance at Evij-tok in Greenland . It is now very largely usedfor the preparation of aluminium. The mineral ispowdered, mixed with half its weight of commonsalt, and either placed in alternate layers with 2parts of sodium in a crucible, or roasted with thesame quantity of sodium in a furnace.
The chief advantage in using cryolite is, that thecostly and troublesome process of preparing thedouble chloride of aluminium and sodium is thusobviated, The metal is, however, less pure. Manypatents have been taken out for improved processes,but they all apply to mechanical contrivances foreconomizing the sodium.
Gerhard proposed to decompose aluminiumfluoride or cryolite by a current of hydrogen at ared heat. The aluminium fluoride, or cryolite, wasplaced in shallow earthenware dishes, alongside ofwhich were like dishes containing iron filings, in anoven which had previously been heated to redness.A current of hydrogen was then admitted and theheat increased. Hydrofluoric acid gas was givenoff and absorbed by the iron filings. This processwas, however, ultimately abandoned by its inventor,who reverted to the rise of sodium.
No processes of aluminium smelting, except thoseof reduction by sodium, have been thoroughly suc-cessful. The progress of the manufacture of alum-inium therefore depends on still more economicalmethods for producing the alkaline metal beinginvented. Mr. J. Lothian Belt, of Newcastle-on-Tyne , manufactured aluminium on the large scalefor several years, but has of late relinquished theundertaking on account of the limited market forthe metal.
Properties. —The physical properties of alum-inium are very characteristic. Its specific gravity is2 - 56; after hammering, 2’57. This low specificgravity, being nearly that of the flux employed infusing it, materially enhances the difficulty of itsproduction. Aluminium is next highest in densityto the metals of the alkaline earths. It is malleable,ductile, and sonorous. A bar of aluminium, whenstruck, emits a clear musical ring; when cast intothe shape of a bell and struck the sound is, however,anything but musical; it more resembles that of acracked pot. The fusing point of aluminium isintermediate between silver and zinc, but nearer tothe latter. It resembles silver in its excellence as aconductor for electricity. Its capacity for heat isvery great, about six times that of silver. Itschemical characteristics are such as could not havebeen predicted. Instead of reassuming oxygen, likethe metals of the alkalies and alkaline earths, withan energy proportioned to the extreme tenacity ofthat element when in the state of oxide, aluminiumis almost as indifferent to oxygen as are gold andplatinum. It is not affected by sulphur as is silverand lead, nor is it acted on, except very slowly, by
nitric and sulphuric acids in the cold. Its only sol-vents are hydrochloric acid and aqueous solutions ofpotassium and sodium hydrates. The strong affinitybetween this metal and oxygen before its separation,contrasted with its apparent total indifference after-wards, suggests the possibility that, at the instantof its coming in contact with air, aluminium mayreceive a fine coating of oxide, a film of transparentsapphire, from the atmosphere, which protects itfrom all further action. This conjecture is ren-dered probable by the result obtained on exposinga leaf of aluminium to the oxidizing flame of theblowpipe. The result of the combustion, thoughapparently a mass of alumina, shows by its metalliclustre, when rubbed in an agate mortar, that theoxygen has not penetrated below the surface.
Alloys. —Aluminium forms alloys with nearly allmetals. With zinc and iron it forms brittle com-pounds. With silver it also forms a brittle alloy,unless the proportion of silver be very small—3 to 5per cent. Silver alloys are used for making manyornamental articles, and are said not to be tarnishedby sulphuretted hydrogen.
Aluminium Bronze .—This is the most importantof the aluminium alloys. It is a definite compound of copper and aluminium, which has the formulaCugAl. This substance is somewhat largely usedas a substitute for gold, which it closely resemblesin colour. It takes a high polish, is very malleablethough hard, and possesses a tenacity equal to thatof steel.
AMMONIA. — Ammoniacal Gas. — Ammoniaque ,French; Ammoniak , German. Ammonia is synony-mous with the alkaline air of Priestley, volatilealkali, &c. Formula, NH 3 .
Gaseous ammonia was probably known to the an-cients, though no record of the fact remains to proveit; still, as the manufacture of ammoniacal salts was asource of trade among the Egyptians, it is very pro-bable the pungency of the gas was familiar to them.Ammonia was noticed by Raymond Lully in thethirteenth century, who prepared it from urine; thename he gave to it was mercurius vel spiritus animalis.Basil Valentine , in the fifteenth century, separatedammonia from sal-ammoniac; he termed it spirillaurinse.
The scientific development of this compound re-mained for Dr. Black, who in 1756 first isolatedthe gas, and proved its distinction from the sesqui-carbonate, (NII 4 ) 4 II 2 (C0 3 ) g ; Priestley afterwards,in 1774, with greater accuracy, in a more lengthenedinvestigation, prepared it in a pure state, and dis-covered more of its properties, and noticed its decom-position by the electric spark. Sciif.ele, in 1777,discovered that ammonia contained nitrogen. Berg-MANN gave it its present name, ammonia, in 1782;and its true chemical composition was worked out byBerthollet in 1785, and corroborated by his son in1808.
Ammonia, though not very extensively dissemi-nated in nature, is to be met with in a great manyvegetable products; the decomposition of animalmatter, either by putrefactive fermentation or de-