A L U 



A'Luaf . (alumen, Lat. alun, Fr. allume, 

 It.) A triple sulphate of alumina 

 and potassa. Alum is both native 

 and factitious. The common mode 

 of obtaining alum is by roasting 

 and lixiviating certain clays con- 

 taining pyrites ; to the leys a 

 certain quantity of potassa is added, 

 and the triple salt is obtained by 

 crystallization. Alum has a sweet- 

 ish astringent taste. It dissolves 

 in five parts of water at a tem- 

 perature of 60, and the solution 

 reddens blues. 



A'LTJM-STONE. The shale from which 

 alum is extracted. An enormous 

 bed of alum-shale exists near 

 Whitby, in Yorkshire ; from this 

 bed, alum has been manufactured 

 ever since the days of Queen 

 Elizabeth. The depth to which 

 this stratum reaches, says Mr. 

 Winch, has never been ascertained, 

 but, to give an idea of its thickness, 

 I need only mention that the cliffs 

 at Bowdly are 600 feet high, 400 

 of the lower part being an entire 

 mass of shale ; and to what depth 

 it may extend below the level of 

 the sea, remains to be proved. 

 ALTJ'HINA. \ This substance obtained 

 A'LTJMINE. > the name of alumina 

 A'RGIL. ) from its forming the 

 base of common alum, and that of 

 argil from the Lat. argilla, clay, on 

 account of its being a constituent 

 of clays ; clays are termed argil- 

 laceous substances. It is found in 

 the greatest purity in corundum 

 and its varieties ; it is a sesqui- 

 oxide of aluminium. Pure argil- 

 laceous earth, or alumina, is a 

 substance which in a mixed state 

 is well known, but pure and un- 

 mixed, is one of the rarest sub- 

 stances in the mineral kingdom. 

 This earth is soft, smooth, and 

 unctuous, to the touch. Combined 

 with other earths, or rocks, it 

 communicates to them some of 

 these properties ; such rocks are 

 termed argillaceous. Alumina con- 



L 15 ] A L U 



stitues some of the hardest gems, 

 such as the ruby and sapphire, the 

 latter being crystallized alumine. 

 According to the analysis of Kla- 

 proth, the sapphire contains 95 per 

 cent, of pure clay. Alumina was 

 considered an elementary substance 

 till Sir Humphry Davy's electro- 

 chemical researches led to the 

 opinion of its being a metallic 

 oxide. Next to silicium, aluminum 

 would appear to be the most im- 

 portant base of the earths on the 

 face of the glode. Its collective 

 amount is by no means so great as 

 that of silicium, but it is quite as 

 widely spread. There is scarcely 

 one among the mechanical rocks 

 that does not contain alumina. It 

 constitutes the base of the various 

 clays, and must be regarded as a 

 very abundant and important con- 

 stituent part of rocks. It contains 

 46-8 per cent, of oxygen. De la 



ALTJ'MINITE. Sub- sulphate of alumine. 

 A white mineral, dull, opaque, and 

 having an earthy fracture. This 

 mineral occurs massive, in veins, 

 and in tabular and tuberose masses; 

 the former frequently attaining a 

 length of several feet, and the latter 

 a weight equal to three or four 

 pounds. It appears to have been 

 of stalactitical origin, and is sup- 

 posed to result from the decompo- 

 sition of iron pyrites, and the re- 

 action of other substances. It is 

 infusible at 166 of Wedgewood, 

 but fuses rapidly when exposed to 

 the stream of the hydro-oxygen 

 blow-pipe. According to the anal- 

 ysis of Stromeyer, it consists of 

 alumine 30, sulphuric acid 25, 

 water 45. 



A'LTJMINOUS. Having the properties 

 of alum; containing alum; re- 

 sembling alum. 



ALTJ'MINUM. The metallic base of 

 alumina. The metal itself has not 

 yet been obtained in a separate 

 state, but the analyses to which 



