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riatt 1. CoralPiMSt kc. fig. u Phil. Traiif. vol. lili. 

 p. 427. 



AGARICUS S'l'ias, in Jucieiit Gtcgraphy, a gulj))! of 

 India, on this Cde the Gan^^cis, according to PtoUniy. 



AGARON, in NuturarBijhry, a name given iiy Adan- 

 f'.n to a fpecies of voluta; the ifpidula oi Gnuhn's edi- 

 tion of th,- L:;ina-an Syllcin. 



^AGARRA, in yhcliit G.csrafhy, a town of Snfinna, 

 m Alia } placed by Rolemy in lon^. Ss*" 40' ; and lat. 

 33" 20'. 



AG.-\RUM, a pr&mcntor)' of Atiatic Sarmatia, near 

 the river jigiirus, which rail from north to fouth, and dif- 

 chargrd ilfclf into the Pi:!us Maolis. According to Ptolemy, 

 itwa's lituated in long. 63°, and lat. 49° 40'. Ovid. (Pont. 

 jv. 10.) c.'ills the river, Sagaris ; and it is now Sa^ir. 



AGASUS, a -port mentioned by Pliny, fituate between 

 the promontoiy of Garganus and the river Cerbalus; and 

 fiippofed to be the fame with Por:o Greco. Agafus, or Agafla, 

 was alfo a town of Macedonia in Europe. 



AGASYLLIS, in the MaUria Mcdka, a name given 

 by fome of the ancient Greek writers to gum ammoniac ; 

 and by Diofcoridcs, to the tree which produces that gum. 

 By their dcfcription of this medicine, it appears not to have 

 been the fame which we know by this name. 



AG ATA,iny/««V«/ Geography, a fmall town and bilhop's 

 fee of Naples in the Principato Ultra. 



AGATE, A'/a.'!i<i yichaUs, of Theophrallus and Pliny ; 

 Agalh, Fr. Achat, Germ. Agakr, Swed. This wcid 

 is ufed by modern m.ineralogiils not as denominating any 

 particular fpecies of ftone, but a filiceous mixture of quartz, 

 hornftone, flint, calcedony, amethyll, jafper, carnelian, cr 

 heliotrope, aggregated into binary or more complex combi- 

 nations. It has nevertlielcfs feveral peculiar charaftcrs by 

 which it may readily be dillinguillied from other minerals. 

 Although it confifts of paits differing in colour and tranf- 

 parency, yet thefe poffefs a certain uniformity of arrange- 

 ment, and Hide into each other by fuch nice gradations as 

 (how them to have been all of limultaneous formation ; and 

 hence it differs from filiceous Breccia, in which angular 

 fragments of filiceous pebbles are cemented by a filiceous 

 paite : for in all thefe the cement, whether quartz, calce- 

 dony, or flint, is wholly diftinft from the fragments that it 

 inveils, and the arrangement of the whole is merely cafual. 

 As it differs in tlie colour of its conftituent parts, fo it does 

 in their tranfparency ; it is never wholly opaque like jafper, 

 nor tranfparent as quartz cr^-ftal : it takes a very high 

 polifh, and its opaquer parts ufually preient the appearance 

 of dot-s, eyes, veins, zones, bands, or ramifications. Its 

 colours are yellowifh, reddiih, bluifh, or milk white, honey- 

 orange, or ochre yellow, fleih blood, or brick red, reddifii 

 brown, violet blue, and brownilli green. Specific gravity 

 from 2.55 to 2.7. It gives fire with fteel very plentifidly. 



It is found in the form of irregular rounded nodules, 

 from the fize of a pin's head, to more than a foot in dia- 

 meter; orin ftrata, and fometimes, though rarely, ilalaftltic. 

 Several varieties of agate are diftinguiflied by the lapidaries : 

 the finer femi-tranfparent kinds, confilling principally of cal- 

 cedony, are called oriental : in the banded agates the co- 

 lours are difpofed in ftrait parallel lines or bands ; while in 

 the fortification agate, the mofl beautiful of all the varie- 

 ties, they are arranged in waved and angular concentric 

 zones : the landfcape agate, by the name alone, fulKciently 

 declares its irregular appearance : the n.ofs agate, or Mochoa 

 ftone, is filled with dendritical cryftailizations of iron ore, 

 fo nearly refembling fome kinds of mofs, as to have been 

 aftually mifi;aken for real vegetables by Daubenton. 



Agates are foimd, for the moft part, in argillaceous por- 

 phyry, occafionally in gypfum, near the river Wolga they 



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occur between the ftrata of fecondaiy limeftone, and certain 

 rocky tracts in Siberia confill almoll entirely of a pudding- 

 ftone, of which agates and calcedony form an effential con- 

 llitUvUt part. The aigiUaceous porphyry being a rock 

 that is eailly difintegrated by the aftion of the air and moif- 

 t'uc, the agates and other liliceous pebbles that it contains 

 Tail out and are walhcd by the rains into the beds of rivers ; 

 here, by friiiion upon each other, t'.ic afperities on their fur- 

 face are worn off, and in this ilate they are generally found 

 on the fea-(hore and in gravel beds. The mofl beautiful 

 agates that this ifland produces, are commonly known by 

 the name of Sccich pMLs; thefe are met with in various 

 parts of Scotland, but principally in the vicinity of Dunbar. 

 The agates of (iennany are the largeft, efpecially thofe 

 from Kunerfdorf in Saxony. The Dutchy of Deuxponts, 

 the Palatinate, Plcffe, Thuringia, Wirtemburg, Bavaria, 

 Bohemia, and Sik-fia alfo furnifli them in great abundance. 

 The river Achates in Sicily was of old celebrated for thefe 

 pebbles, and hence they have acquired their name : the 

 other parts of Eui-ope, where they are found, are principally 

 Tufcan)', Candia, and Iceland. Some cxquifitely fine fpe- 

 cimens have been brought from Siberia, and the ifland of 

 Ceylon ; and they have lately been difcovered in great 

 plenty in the bed of a river at the eaflern extremity of the 

 fettlement at the Cape of Good Hope. 



The ufes of agate are principally for ornamental works ; 

 the engraved gems, thofe precious remains of ancient art 

 are principally agate, and much ingenuity has been fliewn in 

 the accommodation of the natural veins and marks to the 

 figures engraven upon them ; it is alfo mvich ellecmed by 

 modern lapidaries for feals. Small mortars are made of 

 agate, and are ufed by the enameller, and in the laboratory 

 for grinding fubflances that are too hard to be triturated 

 any other way. 



A dark i1:ain approaching to red, or red purple, may be 

 communicated to agate, by heating it in warm aflies, and 

 then moiftening its furface with nitro-muriat of gold, or 

 nitrat of filver ; when the ftone is become dry, it muft be 

 fet for a day or two ip a dark moift place, and then expofed 

 to the full fun : by this method tlie moft delicate zones 

 and ramifications, which are not vifible in the natural uate 

 of the ftone, are made to appear in a very beautiful manner ; 

 this tinge is, however, deftroyed by nitrous acid, or a mode- 

 rate heat : and thus artificial trains may be diftinguiflied 

 from the native col;)U"3. A deep black is given to agate 

 by foaking it when heated, in boiling nitrat of copper, and 

 then heating it nearly to redncfs in a covered crucible. 

 Mochoa ilones are imitated by fpreading a folution of ni- 

 trated copper over the furface of a plain agate, and then 

 fetting a fmall iron nail on its head in the middle ; the ni- 

 trous acid unites with the iron, and depofits the copper in 

 beautiful arborefcent radiations from the centre ; the nail 

 muft then be removed, and the furface carefully wafted, by 

 dipping the ftone in warm water ; afterwards on the appli- 

 cation of a moderate heat, the copper becomes black. — 

 This depofition, however, being merely fuperficial, requires 

 to be covered with a plate of polifted ciyllal, in the man- 

 ner of a doublet. If the ramifications are required to be 

 very fine, the agate fhould be moiftened with a dilute nitrat 

 of filver fujierfaturated with the metal, or a folution of 

 lunar cauflic in water, a fmall piece of zinc is to be placed 

 in the middle till the ramifications are fufficiently far ad- 

 vanced ; the ftone muft then be waflied carefully in warm 

 water, and afterwards expofed to fulphurated hydrogen gas, 

 till the filver is become black. 



Agate is faid to be imitated very fuccefsfully in glafs ; 

 and Nt-ri, in his " Art de la Verrerie," gives three different 

 receipts for this puipofe : of thefe the following is recom- 

 mended 



