106 



ALUM 



Btone suitable for alum in tho inland Ischia ; ho burnt it, and obtained a good result, 

 being the first who introduced tho manufacture into Europe. This was in tho year 

 1459 ; about the same time John di Castro learnt tho method at Constantinople, and 

 manufactured alum at Tolfa. This discovery of the mineral near Civita Vecchiu was 

 considered so important by John di Castro, that ho announced it to the Popo as a 

 great victory over the Turks, who annually took from tho Christians 300,000 pieces 

 of gold for their dyod wool. A statue wag erected to tho ' Discoverer of Alum.' 

 Beckman. 



The manufacture of alum was then made a monopoly of the Papal Powers, and 

 instead of buying it as before from the East, it was considered Christian to obtain it 

 only from the States of tho Church, and, as such, was made compulsory in tho West. 

 The manufacture then went to Spain, to a spot near Carthagena. Germany began 

 so early as 1554 to make alum, although Basil Valentine seems to have known of its 

 existence there somewhat sooner. Tho first establishment known was at Oborkauf- 

 ungen in Ilesse-Cassol, where it still exists. It was not introduced as a manufacture 

 into England until the year 1600, when Sir Thomas Chalonor, tho son of Queen 

 Elizabeth's minister of that name, found that his own estate of Guisborough, in 

 Yorkshire, contained alum. This ho is said first to have observed from tho 

 vegetation, which had a very weak green. Di Castro had first been led to it 

 by the appearance of tho holly, but neither can be said to bo decisive tests of its 

 presence, nor are the geological features of Tolfa and Guisborough at nil alike. The 

 violent denunciations of the Pope did not prevent tho manufacture from growing to 

 unexpected magnitude in England. The mines of tho same district have over since 

 sent out alum, which is now known as Whitby alum, and oven those at Guisborough 

 itself are now at work, although for seventy years of tho period since their discovery 

 they wore disused. The manufacture was begun at Hurlet, in Scotland, by Nicholson 

 and Lightbody, in 1766, abandoned, and resumed by Macintosh and "Wilson in 1797. 



The chemical composition of alum varies with the nature of tho bases present, but 

 all alums are constructed on a common type, expressed by the general formula 

 MO. SO 3 . M 2 3 . 3S0 3 + 24HO. They are, therefore, double sulphates, containing both 

 a protoxide and a sesquioxide, combined with a constant number of molecules of water. 

 The protoxide is generally an alkali usually potash or ammonia but other alums 

 are known, though at present of no importance in the arts, in which the metal of tho 

 protoxide is silver, thallium, caesium, or rubidium. On the other hand, the sesqui- 

 oxide, though generally alumina, may take the form of sesquioxide of iron, of 

 manganese, or of chromium. It is desirable to exhibit this relation between some of 

 the more important alums ; and, as the formulae representing these double salts aro 

 s.omewhat complex, it may be useful to compare their symbolic expressions con- 

 structed with both the old and tho new atomic weights : 



The composition of pure potash~alum may bo represented centesimally and atomi- 

 cally as follows : 



Per Cent. Per Cent. 



Potash . . 9-89 or 1 atom 47 1 



-i'S: iTS 



Water . . 45-49 24 216 J 

 Its specific gravity is 1*724. 



100 parts of water dissolve, at 32 degrees Fahrenheit, 

 50 

 86 

 122 

 158 

 212 



Those Tables of Poggiale should be ro-examinod, and gradations made more useful 

 for this country. 



18-32 or 1 atom 27 

 36-21 1 172 

 45-48 1 ,, 216 



3-29 alum 



9-52 



22-01 



30-92 



90-67 



357-48 



