GOLD. 



The brown cubic crytlals from Ccrcfof, in Siberia, wliicli 

 contain grains of gold, arc- confid'-rcd by fome as dcuonipoU 

 ed, by others as hepatic pyrites, and by fome as brown iron 

 (lone in fuppofititious cryilals. Whatever they may be, lliey 

 are certainly not what Werner means by hepatic pyrites. 



^. The native gold of Tranfylvania is often accompanied, 

 and fomctimes incrulled, by particles of a pale yellow earthy 

 fubttance, whicli was conlidered by Hacquet as an oxyd of 

 gold. Muller and others have deftribcdit as iron-ochre, from 

 which, howevei-, it appears to differ both in colour and 

 conlillence. It is almoft always to be met with in the fpe- 

 cimens of native gold from Veredipatak, but fometimes in 

 fuch fine particles as to appear merely as a taruilh on the 

 metal. It is to this dull probably that tiie gold ore, called 

 Spanilh fnuff, owes its mat, yellowifh-brown colour. It de- 

 ferves further examination. 



4. The grey metallic fubflance occurri)ig as acicular 

 indeterminate cryftals, along with the gold of Siberia, ni 

 quartz, and which has been defcribed as tellurium, as grey 

 copper ore, &c. appears to be native bifmuth. 



For the chemical charaaers of gold, and the ufcs to \\ hich it 

 is applied, fee the fequel of this article. 



Extraction of Gold — Tiiis metal is obtained feparate from 

 foreign fubftances, with which it is mixed by amalgamation 

 with quickfdver. After it has been freed, by pounding and 

 wafliincr, from the ftony matter, it is triturated with about 

 ten times its weight of mercury. The more fluid part of 

 the amalgam is forced through leather, while that which is 

 more confiftent, and which contains the cliief part of the 

 gold, remains. This is fubjected to dillillation, the quick- 

 iilver is leparated and evaporated, and the gold remains in a 

 ftate of fulion. When this metal is found in other ores, they 

 are firft roafted, to dii'perfe the volatile principles, and to 

 oxidize the other metals. The gold, which is but little 

 fubjeft to oxyddtion, is extrafted by amalgamation, by cu- 

 pellation, or other methods adapted to each ore, according to 

 its properties or conftituent parts. The metal obtained in 

 thefe ways is always more or lefs alloyed, particularly with 

 filver and copper. The firfl; ftep in its purification is tlie 

 proeefs of Cupellation, to which article in our Cyclopxdia 

 the reader is referred for accurate information on this part of 

 the fubjcd. 



The gold, after it has been fubmitted to tliis proeefs, is 

 often alloyed with filvcr, which, being nearly as diflicult of 

 oxydation, is not removed by the action of lead, and hence 

 the neceffity of the operations denominated Parting and 

 Quartation, which may be explained in a few words. 



In Parting, the metal is rolled out very thin, and cut into 

 fmall pieces, which are digeftcd in diluted nitric acid mo- 

 derately hot. The acid lias an aftion upon, and difiolves 

 the filver, leaving the gold undiffolved in a porous mafs. 

 When, however, the proportion of filver is very fmall in 

 comparifon of the gold, the latter fometimes protefts tlie 

 former from the action of the acid ; in fuch cafes tl;e pre- 

 vious flep of Quartation is employed, which is lo named on 

 account of the proportion of materials employed, T/'t. three 

 parts of filver, with one of gold, and then lubjecting the 

 alloy, rolled out, to the operation ot the acid. Sometimes 

 tliey are melted together, and fulphur thrown in, the ful- 

 phur combines witli the filver, and the gold falls to the bot- 

 tom. It is obferved bv Lagrange, that rolling and annealing 

 are operations very necelTary to the fuccefs ot the parting 

 proeefs, and which recjuire fome precautions. I ft. The 

 plate mufl not be too thin, left it lliould break in confequcnce 

 oi the motion communicated to it bv the action of tlie acid ; 

 : if it is too thick the acid could not penetral? to its centre. 



zdly. The annealing of the plate, at the fame time that it gives ■ 

 pliability, facilitates its being rolled without cracking ; it alfo 

 opens the pores of the metal, wliich the rolling may have 

 prelfed together, and by thefe means favours the adtion of 

 tlie acid. 



The proeefs recommended by Bergman is this: firft to 

 difTolve It in nitro-muriatic acid ; the filver is dcpofited f pon- 

 taneoufiy in the form of muriate of filver, which is infoluble ; 

 tlie gold is precipitated in fine powder by the fulphate of 

 iron. Kacli of the above-mentioned procefles is performed in 

 fuch a manner as to lead to an eflimate of the quantity of 

 gold, and alio of the difTerent metals with which it is al-' 

 loycd. 



Gold, it is faid, by fome able French chemifls, as I,^ 

 Sage and Rouelle, exills in the vegetable kingdom, it 

 having, in experiments inftituted for the purpofe, been ex- 

 tracted from the aihes of certain plants ; the quantity, how- 

 ever, being, of courfe, too trifling to be fought after for 

 pradtical purpofes, it is fufficient merely to mention the 

 fart in this place. 



Gold, Chetnical Properties of. — Gold melts at the tcinpera- 

 ture of 32"'of the fcale of Wedgeuood ; and what is very 

 remarkable is, that it is more difficult of fufion in the ftate 

 of filings and grains, than in larger mafTes ; and that the 

 fmall fragments, even after they are fufed, remain in feparate 

 globules : and in order to make tlicm run into one mafs, a 

 little nitre or borax is thrown into the crucible. Gold, 

 w hich has only been fubjedted to a degree of heat barely ne- 

 celTary for its fufion, is brittle after cooling. To preferve 

 itsdurtility, which, as will be i'een farther on, is one of the 

 more important meeh,*nicnl properties of gold, the tempe- 

 rature mull be railed much liigher. It is brittle alfo when 

 it is too fuddenly cooled alter fufion. By an incrcafe of tem- 

 perature while the gold is in tufion, it becomes convex on 

 the furface, and when it cools, it finks, circumflances which 

 are afcribcd to the expanlion and contrattion of the metal. 

 When it is gradually and flowly cooled, it cryflallizes in the 

 form of quadrangular pyramids, or regular octahedrons. If 

 the heat be continued while it is in pcrfeft fufion, it feems to 

 undergo akindot ebullition. Thiscircumftance wasnoticedby 

 Homberg and Macquer,as well in tiie application of the burn-' 

 ing-glafs, as when a fmall globuleof the metal wasatledon by 

 the blow-pipe. Macquer afTcrts that it rofe in vapour to tlie 

 height of five or fix inches, and attached itfelf to the furface 

 of a filver plate, which it completely gilded. 



The flrongeMl: heat of a furnace, which has been applied 

 to gold in fufion, has been found incapable of producing tlie 

 fmallefl change or the leaft tendency to oxydation ; but, by 

 the aftion of a very powerful buriiing-glafs invented bv 

 Tfchirnhaufen, and whicii has been defcribed under tiie arti- 

 cle KvUN'lNo-GLAS.s, Hoiiiberg found that gold, placed 

 in its focus, not only rofe in vapour, but that it was covered 

 with a violet-coloured vitreous oxyd. The experiment was 

 frequently repeated, lo as to afcertain the fatt moll coir.plete- 

 Iv. The fame thing has been done by means of the elettnc 

 difcliarge, by wliicli gold-leaf, placed between two cards, 

 has been converted into a violet-coloured powder. Tliefe iiu 

 flances of real oxydation were, at firft, regarded, by fome 

 who witnefltd the experiments, as merely minute nieclianical 

 divifions of the metal, but this apparent objetlion has been 

 removed by the experiments of Van Marum on thecombulli- 

 bility of gold by means of the large eleftrieal machine at 

 Haerlem. A llrong elertrical fiiock was paffed througli a 

 golden w ire fufpended in tlie air. It kindled, burned with a 

 ])erceptible green flame, and was reduced to fine powder, 

 whicli was diflipated in tlie air. A fimilar oxydation iias 

 been obferved to take place on the gilding in the inlide of 



houlvii, 



