IS* 



ALl'M. 



ALl'M. 



the approach** to cities, u the sepulchre* were always without the 

 wall*. The Appuu Way WM the must magnificent of these streets 

 of tomb* in toe iieighU>iirlitl of Home, ami unmt liave. exhibited, 

 liUrally. thoiuoixU of sepulchral monument.-*. Though generally the 

 work of Greek artiste, ana often interesting from being copies of better 

 work* now lost, the haste and inattention with wliirli Midi prodiKiouH 

 number* were executed, tended to degrade the Ktyle of their sculpture. 

 In these rilifvi, even in tin- U'ttvr |xvi!neu, buildings and other 

 objects are oocasioually introduced behind the figured, thus .,; 

 ing the spurious style of relief in which the effects of perspective are 

 attempted to be expressed : a great variety, of various degree* of 

 excellence, are to be seen in the British Museum. The greater part of 

 what are called Roman baasi-rilievi are of this kind, and may be con- 

 sidered a middle style between the pure Ureek rilievo ami the modern 

 Italian. It was from antique sarcophagi, fine in execution, but with 

 these defects in style, that Niccola da Pisa, in the 13th century, lii -' 

 caught the spirit of ancient art. Many of the works from which he l- 

 believed to have studied are still preserved in Pisa. D'Agincourt gives 

 representation of one of the beet In imitating the simplicity of 

 arrangement, and, in a remote degree, the purity of forms which these 

 works exhibited, the artist was not likely to correct the defects alluded 

 to, which had been already practised in Italy and elsewhere. Various 

 degrees of relief, background figures and objects, and occasional at- 

 tempts at perspective, are to be found in the works of the Pisani and 

 their scholars, yet their works, which are to be regarded as the infancy 

 of Italian art, and which undoubtedly are rude enough in workman- 

 ship and imitation, are purer in style than those of the succeeding 

 Florentine masters, who attained so much general perfection in sculpture. 

 The rilievi of Donatello are mostly in the style called by the Italians 

 ttiafciat'i, the flattest kind of mezzo-rilievo, according to the definition 

 before given, which he probably adopted, as he worked in bronze, from 

 the facility of casting ; yet in such a style, commanding little distinct- 

 ness from its inconsiderable projection, he introduced buildings, land- 

 scape, and the usual accessories of a picture. But this misapplication of 

 ingenuity was carried still farther by Lorenzo Ghiberti, in the celebrated 

 bronze doors of the baptistery, or church of Son Giovanni, at Florence, 

 which exliibited such skilful compositions, in which the stories are so 

 well told, and in which the single figures are so full of appropriate 

 action. In these works the figures gradually emerge from the itiacciato 

 style to alto-rilievo. They ore among the best specimens of that mixed 

 style, or union of basso-rilievo with the principles of pointing, which 

 the sculptors of the fifteenth century and their imitators imagined 

 to be an improvement on the well-considered simplicity of the ancients. 

 In these and similar specimens, the unreal forms of perspective build- 

 ings, and diminished or foreshortened figures, which in pictures create 

 illusion, when aided by appropriate light and shade and variety of hue, 

 are unintelligible or distorted in a real material, where it is imme- 

 diately evident that the objects are all on the same solid plane. Even 

 Vasari, who wrote when this mixed style of rilievo was generally prac- 

 tised, remarks the absurdity of representing the plane on which the 

 figures stand ascending towards the horizon, according to the laws of 

 perspective ; in consequence of which, " we often see," he says, " the 

 point of the foot of a figure, standing with its back to the spectator, 

 touching the middle of the leg," owing to the rapid ascent or fore- 

 shortening of the ground. Such errors, he adds, are to be seen " even 

 in the doors of San Giovanni." Lorenzo Ghiberti, like other Floren- 

 tine sculptors, first learnt the practice of his art from a goldsmith, and 

 the designs of the artists who competed with him for the honour of 

 executing the doors of San Giovanni were submitted to the judgment 

 of goldsmiths and painters as well as sculptors. 



The taste of the Florentines in basso-rilievo was thus greatly influ- 

 enced by the prevalence of a style most applicable to the precious 

 metals, in which a general sparkling effect is best insured by avoiding 

 uniformly violent relief, which projects considerable shadows, and 

 especially by avoiding unbroken flatness. The background is thus 

 filled with slightly relieved distant objects, so as to produce everywhere 

 a more or less roughened or undulating surface. The same end seems 

 to have been attained in the antique silver vases, by the introduction 

 of foliage. The style continued to be practised with occasionally 

 greater absurdities than those before alluded to, and pcrhajw less 

 redeeming excellence, till the close of the last century. The sculptor 

 Falconet says of the antique, bassi-rilievi, that " however noble their 

 composition may be, it does not in any way tend to the illusion of a 

 picture, and a basso-rilievo ought always to aim at this illusion." II.- 

 leaves no doubt as to the literal meaning he intends by citing the 

 Italian writers who applied the term yaadru indiscriminately to picture 

 and basso-rilievo. Sculpture in this country was indebted principally 

 to FUxm&n for the revival of a purer taste in the application of basso 

 rilievo to architecture. In works of decoration, intended to be executed 

 in the precious metals, in which, as before observed, moderately embossed 

 and general richness of surface U so desirable-, in order to display the 

 material as well as the work, he, however, united hi* own purity of 

 taste and composition with an approach to the mixed style of relief 

 practised by the Florentine master*, who, in this branch of sculpture, 

 perhaps never equalled hix shield of Achilles. 



ALUM. (KO, HU. + ALp,, 88O. + 24 oq > or (NII.O, 80. + A1.O,, 

 880, + 24 aq.) Alum as met with in commerce is a double salt, one of 

 the constituents of which is sulphate of alumina, and the other cither 



sulphate of potash r sulphate "f ammonia. These two descriptions of 

 alum arc distinguished respectively by the name* potath alum, and 

 ammonia alum. Potash alum is occasionally met with n* a natural 

 product in volcanic districts. It is there formed l>y t! 

 milplmric acid upon lavas and trachyte* containing potash ami alumina. 

 I'mler them circumstances it is found at Auvergne in the .South of 

 France, in Sicily and the adjoining volcanic islands, also in the 

 1, ui ln l of N'aple-. a: tin' ilrotto ill Alume |(':i)K> Miseno), and at 

 Solfataro. The alum forum an encrustation on the surface of tin: 

 volcanic rocks, and being dissolved in water, it is recrystalUse< I 

 the mechanical impurities have been removed by subsidence. His then 

 sent into the market as Roman alum. 



Such natural alum constitutes, however, but a very small pro] 

 of that used in the arts. For several centuries alum has been made in 

 thin country, from deposits found at Whitby in Yorkshire, and at 

 Hurlett and C'ampsie near Glasgow, and known as Alum Schiit or Mm, 

 Shale. This material contains, amongst other ingredients, alumina, iron 

 pyrites, and a bituminous or coaly matter. The following U the process 

 employed for obtaining alum from this m ' 



1. A thin layer of brushwood is laid upon the ground, and on tin ; 

 alum schist U piled in a pyramidal form to the height of 90 or 100 

 feet. The brushwood U then ignited, and the combustion gradually 

 communicates itself to the coaly matter of the schist, which is present 

 in sufficient quantity to afford heat enough for the calcination of the 

 whole mass. Great care is taken to cause the combustion to proceed 

 very slowly, otherwise the mass would become partially fused, and the 

 objects of the operation be defeated. From one to two years are there- 

 fore required for the burning of one of these heap*. During th< 

 nation the bisulphide of iron (iron pyrites) is decomposed, and eoim it' d 

 at the expense of atmospheric oxygen into protosulphate of iron MIX! 

 free sulphuric acid, the latter uniting immediately with the alumina of 

 the shale to form sulphate of alumina. These chemical change- may 

 be thus expressed : 



3rcS, + O,, + Al,0, = A1,O,, SSO, + SFcOSO,. 



Iron pyrites. Alumina. Sulphate of Protosulphate 



alumina. of Iron. 



2. When the whole moss has been exposed to the necessary t*-m|H' 

 rature, and has again become nearly cold, it is sprinkled with water 

 from time to time, so as to moisten it thoroughly without interrupting 

 the circulation of air through its interstices ; the object being to oxidise 

 the protosulphate of iron and to convert it as far as possible into 

 insoluble basic persulphate. A certain portion of the iron, how ever, 

 still remains as neutral persulphate, but this probably sutlers double 

 decomposition with the silicate of alumina in the shale, producing 

 soluble sulphate of alumina and insoluble silicate of iron. The mass is 

 now lixivated with water in stone cisterns, when sulphate of alumina 

 nearly free from persulphate of iron dissolves out. 



3. The aluminous liquor thus obtained is now concentrated by 

 evaporation until it attains a density of about 1'4. This operation i- 

 performed in brickwork cisterns lined with lead, thirty-six feet lon^. >-i-\ 

 feet wide, and two or three feet deep, heated by the reverberatory Maine 

 from a furnace placed at one end and fed with highly bituminou 

 Much soot is deposited in the pans, but it subsides, leaving the liquor 

 above it clear. The latter is then run off into tanks and allow id 

 to cool 



4. The cool concentrated liquor is now ready for conversion into 

 alum, which is effected by adding to it a sufficient quantity of a satu- 

 rated solution of sulphate of potash or sulphate of ammonia ; in tin; 

 former case potash alum is produced, whilst in the latter ammonia alum 

 is the result. As sulphate of ammonia is now, in almost all localities, ;i 

 more abundant and consequently cheaper salt than sulphate of potash, 

 it has almost entirely superseded the last-named salt in the alum manu- 

 facture, nearly all the alum now met with in commerce being ammonia 

 alum. A.-< alum is far less soluble ill eold water than sulphate of 

 alumina, it is precipitated in the form of a granular ciy*t,dline powder. 

 termed "alum-meal," when either of the .-ulphatcs just mentii 

 added to the concentrated solution of sulphate of alumina. Tim- tin 

 alum at the moment of its production becomes separated from a numbi-i 

 of other salts, such as the sulphates of iron, lime, magnesia. &<., whieh 

 remain in solution, and the remaining operation* have for their object 

 the rendering of this separation more complete by removing the impure 

 liquor from the interstices of the alum-meal, which is ell,,i,.| In 



ing the latter twice with small quantities of cold water and then i. 

 crystallising it from a boiling saturated solution. The latter op< 

 is performed in vessels termed roorhinrj codtt, which consist of a sufficient 

 number of staves, six feet long, lined with lead, and fitting tightly 

 around a circular flagstone, four to five f<-. t in di.-un. ter, which thus 

 forms the bottom of a cask or vat ; the staves are held together by 

 strong iron hoops, which can be tightened or relaxed at pleasure by 

 crews joining their extremities, thus permitting the casks to l>c put 

 together or taken to pieces with great facility. Into these casks the 

 boiling saturated solution of alum i run ; and as it cools most rapidly 



it is in contact with the staves, a thick crystalline 

 of alum soon attaches to the sides of the cask, and in three or lm 

 days becomes strong enough to retain the interior liquor without the 

 assistance of the stave*, which ore accordingly removed to facilitate the 



