GOLD. 



■with a folution of muriate of gold, tlie fait 13 decompofcd, 

 and the gold, reduced to the metallic Hate, attaches itfelf to 

 the filk. It is decompofed alfo by phofphorus. If a ftick 

 of phofphorus be introduced into » faturatod folution of 

 muriate of gold, the fait is decompofed, and the gold, being 

 reduced to the metallic Hate, forms a cylindrical covering to 

 the phofphorus, which may be feparated by diffolving the 

 latter in hot water. A fimilar effett is produced by burn- 

 ing fulphur, by fulphurated and phofphorated hydrogen 

 gafes, and by fiilphurous acid. If a folution of muriate of 

 gold be cautioufly added to fulphurous acid, a fine pellicle 

 of gold appears on the furface, which is inllantly precipitated 

 in the form of fmall grains. Thefe, and many other experi- 

 ments equally curious and interefting, were firil defcribed 

 by the lady above-mentioned, and tiie rationale of tlie fubjeS 

 is thus explained. All the fubflances which have been 

 enumerated have a flronger affinity for oxygen than gold, 

 fo that the oxyd of gold, in combination with tlie acid, is 

 decompofed ; the oxygen combining with the hydrogen, 

 and forming v/ater, or witli the phofphorus or fulpliur, 

 and forming fulphuric or phofphoric acid. 



The muriate of gold is foluble in ether, and form* with 

 it a folution of a golden yellow colour, which floats on the 

 top of the fluid. By the addition of ether to a folution of 

 gold, and agitating the m.ixture, as foon as it is left at reft, 

 the two liquids feparate, the ether rifes to the top, and 

 aiTumes a yellow colour, while the nitro-muriatic acid re- 

 mains below and becomes white. By a procefs of this kind 

 a tinfture of gold was prepared, called " potable gold " 

 The folution of gold in ether is not permanent : it is quickly 

 reduced to the metallic flate, and is fometimes found cry- 

 ftaUized on the furface. The etherial folution is ufed by 

 Mr. Stodart for defending lancets, and other furgical inftru- 

 ments, from injury by a moift atmofphere. 



The muriate of gold is decompofed by all the alkalies 

 and eartlia, and is reduced to the flate of yellow oxyd. 



Moft of the metals decompofe the muriate of gold : cop- 

 per, iron, zinc throw down the gold in its metallic ftate : 

 other metals, as lilver or lead, in the ftate of purple oxyd. 

 The precipitate obtained by means of tin is valued for the 

 beauty of the colour which it gives to glafs or enamel. 

 This preparation is known to artifts by the name of the 

 " Purple powder of Caffius," and it may be obtained by 

 various proceffes. That which is commonly reforted to, is to 

 difTolve pure gold in a nitro-muriatic acid, which is compofed 

 of three parts of nitric and one of muriatic acid. A folu- 

 tion of tin is to be prepared by diffolving the motal, in fmall 

 portions at a time, in an acid containing two parts of nitric 

 and one of muriatic acid, previoufly diluted with an equal 

 weight of water. This folution, after it is faturated, is 

 largely diluted, perhaps with a hundred parts of diflilled 

 water : to this the folution of gold equal in quantity to 

 half the quantity of folution of tin, is added, and the preci- 

 pitate is obtained after it is allowed to fubfide, which is to 

 be wadied and dried. This is the only known preparation 

 capable of giving a red colour to glafs ; and if the experiment 

 be performed with accuracy and judgment, the glafs fo 

 treated ferves as a capital imitation of the ruby. The 

 procefs is, however, attended with confidcrable difficulty, 

 owing to the colour of the precipitate being various, from 

 circumftances not eafily difeovered. According to Pelletier, 

 it is a compound of oxyds of tin and gold; and its formation 

 is swing to the ftrong attraction of the tin for the oxygen, 

 with which it is difpofed to combine in large quantities. 

 When the folutions, above defcribed, are mixed, the oxyd 

 of tin, which is nearly at the minimum of oxydizement, at- 



trafts part of the oxygen of the oxyd of gold : the tw/» 

 oxyds thus brought to itatcs of oxydizement, different from 

 thofe in which they exifted in the feparate folutions, and 

 probably likewife exerting mutual affinities, are no longer 

 foluble, and are precipitated in combination. Muriate of 

 gold is decompofed by fome other metallic ialts, in coiife- 

 quence of fimilar aiStions ; the oxygen of the oxyd of gold 

 being attracted by the oxyd of the other metal, which 

 hence paffes to a higher ftate of oxydizement. Thofe which 

 have a ftrong tendency to exift in fuch a ftate, are capable 

 even of completely de-oxydizing the oxyd of gold. Ex- 

 ample. — If a folution of the green fulphate of iron be added 

 to the folution of muriate of gold, the gold is precipitated 

 in very minute particles in th'_- metallic (late, ivhile the iron 

 paffes to the ftate of a red fulphate. A folution of muriate 

 of gold, when concentrated by evaporation, yields beautiful 

 yellow cryftals, not unlike topazes. 



Gold, as we have fcen, does not combine v.ith fulphui- 

 by fufion, and on this is founded a method of freeing it from 

 filvcr or other metals, the alloy being fufed with fulphui-, 

 the filvcr, &c. unite with the fulphur, leaving the gold fepa- 

 rate. But gold and fulphur may be united by the medium 

 of an alkali. Example. — Let a fulphuret of potafii be fufed 

 with one-eighth of its weiglit of gold-leaf, and the combina- 

 tion is even foluble in water, the folution being of a given 

 colour. 



AUoxs of Gold. — Gold form.s alloys with the greater 

 number of the metals, which proditce on the m.etal fo ailovcd 

 a very particular change in its properties. An exter.iive 

 and accurate ferics of experiments on thefe alloys was made 

 by Mr. Hatchet, with the view of determining foine im- 

 portant and interefting facls relating to the ufe of gold as .1 

 coin. Of thefe v.-e fliall give a brief ab.'lraft, referring our 

 readers for a more particular account to the TraufaiSlioriS of 

 the Royal Societv for the year 1803. 



The cliief enquiry of Mr. Hatcliet, as conneftcd with the 

 allovs of gold, was, whether foft and ductile gold, or gold 

 made as hard as is compatible with the procefs of coiiiim.-, 

 fuffers moft by wear. His experiments were intended ti> 

 examine the effects v.hitli various metals produce upon gold, 

 when combined with it in given proportions, beginning with 

 T^'-,th, which is the ftandard proportion of aliov, and gradually 

 dccrcafing to -f-^'y^ part of mafs. Tlie refults drawn from 

 the trials were, that fine gold, alloyed with filvcr, with 

 copper, and with tin, did not fufFer any lofs during the 

 experiment. The gold alloyed with lead only loil three 

 grains, chiefly by vitrification ; with iron it loft 12 grains, 

 which formed fcoria ; with bifmuth it loft 12 grains, chiefly 

 by vitrification ; with zinc it loft a pennyweight by volati- 

 lization ; and wi»h arfenic, it not only loft tlie whole quan- 

 tity of alloy, but alfo two grains of tlie gold which were 

 carried off in confeqnence of the rapid volatilization of the 

 arfenic. Hence it was inferred th.at only two metals are 

 proper for the alloy of gold coin, namely, filver and copper ; 

 as all the others either confiderably alter the colour, or 

 diminifli the duftihty of gold. In refpcft to the latter 

 qu:;lity, the different alloys employed in this feries of ex- 

 periments appear to affeft gold nearly in the following 

 dccrcafing order: i. Bifmuth. 2. Lead. 3. Antimony. 

 4. Arfenic. 5. Zinc. 6. Cobalt. 7. Manganefe. 8. Nickel. 

 9. Tin. 10. Iron. li.PIaiina. 12. Copper, and, 13. Silver. 

 The three firil have nearly the fame effeil on gold, and 

 bifmuth is found to render .gold brittle when the propor- 

 tion of that metal is to gold only as i to 1920'; even' the 

 vapour arifing from bifmuth, lead, and antimony in fufion-, 

 produces thele changes. 



■ The' 



