ex 



an 



ALU 



efpecially as the roch alum is the kind ufcj in modicine, 

 and the Brunfwick imitation of it contains arjhiic. The 

 external appearance of the two forts differs but little. The 

 taile of the Brunfwick alum is Icfs llyptic tlian that of the 

 roch alum, it u Ids foluble in water, and when heated to 

 rednefs, it lofcs only 37.5 per cent, of its original weight, 

 while the other U)fes 50 per cent. The roch alum, when 

 pofed to the blow-pipe, becomes opaque, fwells, foajr.s, 

 d is converted into a fpungy white mafs. The r.runfwick 

 alum, on the contrary, fwells'lcfs, fcarcely foams at all, but 

 melts, and becomes of a green colour, exhaling at the fame 

 time an arfenical vapour. Again, the precipitate from a fo- 

 lution of roch alum by potalh or foda, being mixed with bo- 

 rax, fufes before the blow-pipe into a white or yellov.ilTi 

 vvhi'te ; whereas the Brunfwick, by the fame treatment, af- 

 fords a violet-coloured globule : and in laft it is nothing 

 more than common alum, containing a little cobalt and arftnic. 



^ 7. Compar'ifan of Engl'ifi, Roman, Levant, and French 

 Alum. 



The Roman alum, manufaftured at La Tolfa, is the 

 purcft and deareft of a,il ; it is in pieces about the fize of a wal- 

 nut, Ihewhig more or leis of its cryftalline form, and is opaque, 

 on account of a farinaceous tffloi sfccnce with which it is co- 

 vered. Tlie Levant or roch alum appears in fragments of 

 nearly the fame i'lze as the former, but in which the cryftal- 

 line form is more dbfcure ; it is externally of a dirty rofe- 

 colour, and internally exhibits the fame tinge, but clearer. 

 Smyrna is the place whence it is ufually (hipped for Europe ; 

 but' it was anciently made at Roccha, or Edefia, in Syria, 

 whence its commercial name roch-alum. The French alum, 

 that is, Chaptal's, defcribed in (■ 5. is in fmall, clear, colour- 

 lefs cryftals. The Englifh is in large, irregular mafles, confi- 

 derably harder than the others. Equal portions of all thete 

 ■kinds,'being expofed in a muffle to a red heat, were weighed 

 after the intumefcence was over, and the lofs by calcination 

 in the Roman alum was 50 per cent. ; in the Levant alum 

 40 per cent. ; in the French alum 57 per cent. ; and in the 

 EngUfh 47 per cent. Of pure water, at 144° Fahr. Roman 

 alum required 14 times its weight for folution ; Levant 

 alum required 1 2 parts ; French alum 1 3 parts ; and Englifh 

 15 parts. 



Equal parts of thefe four kinds of alum being dijTolvcd fe- 

 pnrately in water, the fame quantity of pruffiated lime was 

 added to each folution. That of the Enghfh alum became 

 fllfhtly blue at the end of a few minutes, as was alfo that of 

 the French alum, though the tint was rather lighter; after 

 iQjme time the Roman alum became faintly blue ; but the 

 •folution of Levant alum was only lightly yellow, the natural 

 colour of the pruffnted lime. After two days an inap- 

 preciable quantity of blue precipitate was depofited from the 

 £n;rhih alum, rather lefs from the Roman and French, and 

 only a few atoms from the Levantine ; the three firlf folu- 

 tions were of a bluifh green tint, but the laft was a very di- 

 lute yellow. 



Equal parts of the four forts were diffolved feparately in 

 pure water, and their earthy bafe was precipitated by an ex- 

 cefs of ammonia. The precipitate from the Roman alum 

 was of a pure dead white ; that of the Levantine and 

 Trench was nearly equal to the Roman ; but that of the 

 Englifh was of a juft perceptible bluifli tint. By calcina- 

 tion in a red heat, they all at firft became blackiih, and 

 ended with being perfectly white. 



Hence is apparent the fuperiority of the Roman alum, 

 and the inferiority of the Englifh, when ufed as mordants 

 for the moft dehcate colours : for other colours, and for the 

 various uies befldes to which alum is applied, each kind may 



3 



ALU 



be ufed indifferontly- The Englifh poffefTes lefs water of 

 cryllaUization than the Roman or French ; and a given 

 weight of it will go fuith^r than the fame quantity of any 

 of the reft, as i 2 per cent, is to be deducted from tlie I^e- 

 vantine, on account of the reddilh inloluble fediment with 

 which it is contaminated. 



^ 8. H'ljlorlcal notice of the introJudlon of alum-t7iaJ:in^ tnt» 

 Europe. 



The ancients appear to have been acquainted only with 

 the native plume alum, which they procured from Lipari, 

 and the nelghbourir.g volcanic iilands. In the 12th, i3tii, 

 and 14th centuries it was manufactured at EdeiTa (Rcccha) 

 in Syria, in the vicinity of Conftantinople, and at FhocCEa 

 (I'oya nova), not far from Smyrna. Bartholomew Perdix, a 

 Genoefe merchant, who had often vifited Roccha, difcovered, 

 about the year 1459, a vein of alum ore in the illand 

 Ifchia, and there eltablidied the firft European manufactory 

 of alum ; foon after John de Callro difcovered the body of 

 ore at La Tolfa. Eftablilhrnents were then made at Viterbo, 

 Volaterra, and ot";er places in Italy with fuch fuccefs, as 

 induced Pope Pius IL to prohibit the importation of Ori- 

 ental alum. In the i6th century this art was introduced 

 into Germany and Spain ; and a little before its conclulioii 

 the Englifh alum-works at Whitby were inftituted by Sir 

 Thomas Chaloner, who had the lionour of being perfonxlly 

 excommunicated by the reigning pope on this very account. 

 The earlieft of the Swedilh works dates no higher than 1 637. 

 Macqufr's Chymifches v.brterbuch von Leonhardi, art. 

 Alaun. Annales de Chimie, vcls. viii. xiv. xxii. xxix. Plinii. 

 Hift. Nat. lib. XXXV. c. 52. Bergman's Eflays, vol. i. Me- 

 moi'res de I'Acad. Royale, vol. v. Eiicyciopedie Method. 

 art. Aiiui. 



Alum, in Chem'flry, Materia Medlca, &c. See SuL- 

 PHAT of Alum'tne. 



ALUMINE. — Pure earth of alum Pure clayet 



OR argillaceous earth. Jilum'ine. — Terre d'alun. — 

 Terre argilleufe, Fr. — Thon-erde, Germ. 



The word alumine has been adopted, without alteration, 

 from the modern French nomenclature, by the majority of 

 Englifh chemiils, as the technical name of pure argillaeeou* 

 earth, on account of its being generally procured by the 

 decompofition of alum, when required to be in a ilate of ex- 

 treme purity. 



Next to filex and lime, alumine appears to be the moil 

 commonly occurring earth in thofc ftony or earthy maffes, 

 of which the globe, as far as we are acquainted with it, 

 is princpially compoied. It forms the eilentia', though f e - 

 dom the grcateft part of all kinds of cl'iys, giving to them 

 the property of ductility or plaflicity when mixed with wa- 

 ter. When in a ftate of more intimate combination witli 

 illex it lofes its quality of plailicity, and gives to the mine- 

 rals in which it enters, the charadters of opacity, of hard- 

 nefs inferior to tliat required for ftriking fire with fteel, of 

 that odour known by mineralogifts under the name of 

 earthy, and of that abfence of cryilalUne form which is 

 called amorphous ; fuch are the immenfe mafTes of flate and 

 argillaceous Ichiftus that abound in almoft all mountainous 

 trails, the boles, the colorific earths, the toadftones and 

 clay porphyries. Alumine, however, occafionally, though 

 very rarely, enters in large proportion into eryllallized mi- 

 nerals, and then in its external charaAers of hardncfs, tranf- 

 parency and luftre approaches very nearly to filex : fuch is 

 the adamantine fpar, inferior only in hardnefs to the dia- 

 mond, and which contains from 80 to 90 per cent, of alu- 

 mine : fuch alfo is the fapphire, which by the analyiisof 

 Klaproth appears to contain no lefs than 98 per cent, of 



pure 



