GOLD. 



perior quality to t}iat produced cither by melting the copper 

 and zinc, or by impregnating the copper witli zinc, by ce- 

 mentriiion and fufion with calamine; which is a nnethod foine- 

 times praclifed. A very ingenious artift, fays Dr. Lewis, 

 who now prepares a gold-coloured metal in grc ..' perfec- 

 tion, has a fine kind of brafs made on purpofe for this 

 ufe. The union of the copper and zinc in fulion, fucccx-Js 

 •bell and with leaft lofs ef the zinc, according to Dr Lewis, 

 by ufing a mixture of black flux and l)orax, or a compohtion 

 of twelve parts of greci: glafs powdered, fix parts of put- 

 afh, two of borax, and one of powdered cliarcoal : when this 

 ■flux is fiifed in the crucible, the copper and zinc are dropped 

 into it ; and when they appear perfectly melted, they are to 

 be vi-ell ftirrcd togetlter with an iron rod, and expeditiouflv 

 poured out. The fame flux will ferve for melting fevtral 

 frefli quantities of the metal. Dr. Hooke gives the follow- 

 ing receipt for making a gold-coloured metal : eight parts 

 of diftilled verdigris, i. e. of verdigris purified by folution 

 in dillilled vinegar and cryftallization, and four parts of 

 Alexandrian tutty, with two of nitre, and one of borax, 

 are directed to be mixed with oil to the confiilence of pap ; 

 then melted in a crucible, and poured into a flat mould firft 

 well warmed. A con:pofitiou of this kind is called auriim 

 Jophiflicum. 



The following method is recommended by Homberg for 

 giving a gold colour to copper, without the addition of 

 zinc ; make an amalgam of one part pure copper, and three 

 parts quickliber ; boil this in river-water for two hours, 

 then diilil off the quickfilver in a retort, and cohobate it 

 once ; take out the copper and fufe it, and it will be found 

 of a beautiful gold colour, more duftile than common cop- 

 per, and extremely well fitted for watch-work, gilding, and 

 the finer machines and utenfils. The celebrated Mr. Pott 

 affirms that a gold-coloured metal may be made from a 

 mixture of copper and tin, and diredls it to be compounded 

 in the follo«-ing manner; Take one half ounce of tin aflies, 

 and four htlf ounces of copper ; melt them wt-ll together 

 in a clofe luted crucible, with a ilrong fire ; or take one 

 half ounce of the pureft tin cut in pieces, and fixteen half 

 ounces of pure copper beaten into thin plates ; lay the tin 

 between the copper-plates, lute the crucible clofe, and melt 

 with a flirong fire. See Prince's Metal and Tombac. 



Silver is tarni(hed fuperficially, by certain vapours, as 

 that of putrified urine, to a colour fo like that of gold, 

 that feveral edifts have been iffued in France to prevent 

 frauds of this kind with regard to wire and laces. 



GoLD-co/oured Pigments. See Pigments. 



GoLD-ioloureel l^arni/h. See I^ACciUER. 



Gold, Croivn, See Coin and Standard. 



Gold, Dutch, is a kind of leaf ufed in gilding. Sec 

 which is copper gilt, or brafs beaten into leaves hke the 

 genuine gold-leaf. It is faid to be made from copper- 

 plates, by cementation with calamine, without fubfequent 

 f '.lion. Tlie thicknefs, compared with tliat of leaf-gold, is 

 as nineteen to fo-ar, and under equal furfaces it is confi- 

 derably more than twice as heavy as the gold. 



Gold, Farthing of. See Farthing. 



Gold, Fine or Pure, is that pur^-ed bv the fire of all its 

 impurities, and all alloy. The Latins call it aurum purum, 

 aunim primum, aurum obrixum, aurum coSnm. 



Ttie moderns frequently call it gold of liuenly-four carats ; 

 but, in reality, there is no fuch tliinir as gold lo very pure.; 

 and there is always wanthig at leaft a quarter of a carat. 

 Gold of twenty-two carats has one part of iDver, and an- 

 other of copper : that of twenty-three carats has half a 

 part, / e. half a twenty-fourth of each. 

 -Bouteroue maintains, that the electrum of the ancients 



was gold of nineteen carats; or four parts gold, and a fiftk 

 filver. 



From an ordinance of king John of ranee, it app»ar» 

 that the gold then ftruck at Paris was of ninet<tn caratt 

 one-fifth ; and yet it is added that it was tlie bell ai:d lincft 

 gold t/.-n known on earth. See Standai.d. 



Gold, Fulminating, aurum fulminans, a precipitate of 

 gold from its M;iro-niuriiitic folution by ammonia, which 

 pofTenes a moll remarkable exploCvc property. See At uiv. 



It is prepared by diluting a folution of muriated g' Id 

 witli fix or eight times its bulk of dillilled water, adding 

 drop by drop liquid ammonia, til! the precipitation ccsft-s ; 

 then let the ) ellow powder thus obtained be ferarated by 

 a filter, \yell waflied in hot water, and afterwards drier'. 

 The fulminating gold, thus procured, will exceed the weight 

 of the original gold by about 33 parts in ico. If a finall 

 quantity, e. g. half a grain, of this powder be held over a 

 candle, in a fpoon or on the blade of a knife, it prefintly 

 explodes \\-ith a ver)- loud report, 'i'his powder (hould be 

 very cautioudy ufed ; the temperature requifite for its ex- 

 plofion is ftated at above 250' of Fahrenheit. Before it 

 explodes, its yellow colour changes to black, and at the 

 moment of its decompofition an inftantancous fla(h is ob- 

 ferved. The principal energy m explofion is directed down- 

 wards, infomuch that two or three grains of it exploded on 

 a moderately tliick (heet of copper will burft a hole in it. 

 This fait is decompofed by an electrical Ihock, but it can- 

 not be ignited by a fpark from eledricity or from flint and 

 fteel. It will vehemently explode by fudden friclion, and 

 therefore, in order to avoid dangerous accidents of this 

 kind, it fliould never be kept in a ground-lloppered bottle. 

 The facility of its explofion is very much incrcafed by high 

 drying ; fo that if it be heated till it becomes black, and if 

 immediately removed from the fire, it will frequently go 

 off by a mere touch. If the fulminating gold be mixed 

 with four or five times its weight of chalk, or fulpnat of 

 potalh, or with any pulverulent fubllance neither fufible nor 

 decompofable at a moderate temperature, and expofed gra- 

 dually to a low heat, it will be quickly decompofed, le.iv- 

 ing merely the purple oxyd of gold. Tlie fame effed may 

 be produced by very cautioully heating the fulminating 

 gold without any addition, removing it from the fire when 

 it has changed its colour, and when cold heating it again, 

 and proceeding in this way till the powder becomes purple, 

 in wiiitli rtate it will have entirely loil its explofive facultv. 

 A fimilar change occurs by melting fuljihur at th.e lowcil 

 poflible heat, and dropping in the ^Imiiiating gold by half 

 a grain at a time, well mixing it ; the fulphur may then be 

 burnt off without danger, and minute grains of metallic 

 gold will be left beliind. " The true theory of the de- 

 compofition of fulminating gold was partially difcovered 

 by Bergman, and has fince been fully ilhiftratcd by Berlhol- 

 let. The former of thefe able chemills Ihewid tliat this 

 fait when decompofed in clofe veffels was reduced to gold, 

 partly in the metallic ftate and partly in that of purple 

 oxyd, and at the fame time a gas was cxtricat.d in bulk, 

 about a thoufand times a« great as that of the original fulmi- 

 nating talt, and wJiicli extinguiflicd flame and aniinal life, was 

 not ablorbed by water, and gave no prccipitr.te with lime- 

 water. BerthoUi't, by decompofiiig the fame fubllance in a 

 copper tube, connected with 3 jar inverted in mercury, 

 obtained azotic gas and a few drops of water, and the 

 gold was reduced to the metallic appeanmce. Now as am- 

 monia is compofed of hydrogen and a/.ot, and as the affi- 

 nity of gold for oxygen is very flight, it is inanifcil that 

 the decompofition and explofion, under the circumilance* 

 already mentioned, are occjlioned bv tlu* oxvvva of the 



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Told 



