C H £ M I 
the water, which fupports part of its weight, and hin¬ 
ders it from breaking} then turn up the mat rats quickly 
and dextroufly, that the water may not efcape in 1'uffi- 
cient quantity to fill the crucible and run over the brim. 
Pour the water out of the crucible ; and road the fphal 
piece .of gold once more in the crucible, covered, amidft 
burning coals, or under the muffle of a cupelling furnace. 
The gold, which, on coming out of the aqua-forris, 
was of the brown hue of oxyd of copper, extremely fra¬ 
gile, and diminifhed in volume, becomes duftile, and re¬ 
covers its colour and metallic brilliancy by this opera¬ 
tion. By the weight of the gold, the quantity of alloy 
it originally contained is known. To aieer-tain with pre- 
cilion the quantity of bafer metal which the gold may con¬ 
tain, a given mais of gold is fuppofed to contain twenty- 
four parts, called carats-, and, for great exaflnefs, each 
carat is divided into thirty-two parts, called thirty-ie- 
co-nds of a carat: if the gold after the afflay has loft: one 
■grain out of twenty-four, it is gold of twenty-three ca¬ 
rats; if it has loft one grain and a half, it is gold of twen¬ 
ty carats fixteen thirty-feconds, and fo fbrth. The weight 
ufed in the allay of gold is called the affay ‘weight , and 
ufuafly confifts of twenty-four grains ; it is divided into 
twenty-four carats, which are likewife fubdivided into 
thirty-two parts: an allay weight, which weighs twelve 
grains, is likewile ufed, but divided into twenty-four 
carats, and the carat into thirty-two thirty-feconds. ' 
Hitherto -we have principally confined ourfelv.es to the 
alloy of copper with gold and filver; but there are other 
mixtures which require Tome Consideration. It Icrae- 
times happens that a large quantity of filver contains but 
a 1’mail quantity of gold: this is called -gilding, and the 
allay is called an affay of gilding. And Sometimes it hap¬ 
pens, alfo, that a large quantity of gold contains a.fmall 
quantity of filver. If-thole two metals alone were mix¬ 
ed, the procefs would be very Ample: it would only be 
neceffliry to diffolve the firft in pure aqua-fortis ; and to 
add lilver to the fecond, and then cupel it with lead. 
But there is ahnoft always a certain quantity of copper 
in both mixtures, which muff be feparated by cupella- 
tion. If it be gilding, which is to be allayed, it will not 
be neceflary to add lilver, fince the greater part of the 
mafs is lilver already ; but, having determined the quan¬ 
tity of lead neceflary to be added, by the ufual methods, 
■proceed to cupellation, as di-refted in the affay of filver, 
but not with fuch a heat as directed in the .afflay of gold. 
The firft part of the allay being finiftied, weigh the but¬ 
ton, which will lliew the quantity of alloy it contained. 
Then flatten it under the hammer, and re-roaft and boil 
with aqua-fortis, as direfled before in the affay of gold, 
taking care to let the liquor fettle after each boiling, 
otherwise the gold, being in fmall quantity, will be pre¬ 
cipitated in a powder; and, the lair time, give the cru¬ 
cible tw r o or three flight knocks, to forward 7 the precipi¬ 
tation, and detach any fmall particles that might adhere 
in the inequalities of the veffel. Then pour off the water 
very gently and carefully; and road the gold again as 
before direfted. The weight of gold makes known that 
of the filver, fince you have only to fubtraft that from 
the weight of the original mafs. In the fecond cafe, of 
a large quantity of gold containing a fmall quantity of 
filver, firft try the mafs by the touchltone, and add as 
much filver as is neceflary to complete the inquartation ; 
then cupel with the proper quantity of lead, according 
to the foregoing calculations: weigh the metallic but¬ 
ton, and proceed in the ufual way of affaying gold, hav¬ 
ing regard, in weighing the refults, always to deduft the 
quantity of filver added at the beginning of the operation. 
Gold is not altered by the molt concentrated fulphuric 
acid, even though heated. The nitric acid appears ca¬ 
pable of diflldving a fmall portion of this metal; feyeral 
chemilts think that this folution is produced rather me¬ 
chanically, than by a true combination. Deyeux, mem¬ 
ber of the College of Pharmacy in Paris, has obferved, 
that the nitric acid diflblves gold only when it is iinoking, 
S T R Y. ' 315 
and charged with nitrous gas; he thinks that the acid 
in this ftate is not pure, and affirms that it is loaded 
with gas, 'and by that means converted into a kind of 
aqu.t regia. The muriatic acid alone, and in a ftate of 
purity, does not fenfibly acf on gold. Scheele and Berg¬ 
man have difcoyf red, that this acid, when oxygenated, 
difl'olves gold abfolutel-v in the fame manner as aqua re¬ 
gia, and forms with this metal the fame fait which is 
ufually obtained with the mixed acid employed to dif- 
lolve it. The folution appears to take place in conic - 
quence of the excefis of oxygen united to the muriatic 
acid ; it is made without feniible eftervefcence, a circu.m- 
ftance common to all metallic iblutions in the oxygenated 
muriatic acid. If gold leaf be (hut up in dole veffcls 
with oxygenated muriatic acid gas, the gold foon dilap- 
pears, and is converted into ayeilow fluid. On opening 
the veffel, it will be found that the gas has been abforbed. 
Scherer obferved, that concentrated oxygenated muriatic 
acid occafioned an immediate inflammation, on coming 
into contaft with gold leaf. 
Aqua regia, or nitro-muriatic acid, has been confidered 
as the true fol-vent of gold ; it does not, however, diffolve 
it better than the oxygenated muriatic acid. As foon as 
the nitro-muriatic acid comes in con tad with the metal, 
it attacks it with an eff-.rvefcence which is fo much the 
ftronger, as the acid is more concentrated, the tempera¬ 
ture higher, and the gold more minutely divided. The 
operation may be baldened by a .gentle'heat, or at Jeaft its 
commencement may be forwarded.; the. bubbles fuc- 
ceed each other without intenpiiffion till a portion of the 
metal is diffo.lved, after which this appearance gradually 
ceafes, and cannot be renewed but by agitation or heat; 
nitrous-gas is difengaged during this folution. The ni¬ 
tre-muriatic .acid,'when Iht-u rated. with as much gold as 
it is capable of taking up, is, of a yeliow colour, more or 
let’s deep, confiderabiy caullic, corrodes animal matters, 
and tinges them of a deep purple colour. By cautious 
evaporation it.affords cryftals of a beautiful gold colour, 
refejnbl.ing topazes, and appearing to confift of truncated 
odfahedrons, and fometimes tetrahedral prifims. This 
cryftallization is not eatily effe&ed. Bergman confiders 
this fait as-a true muriat of gold : if the cryftals be heat¬ 
ed, they melt and affume a red colour. This f.ilt ftrongly 
attradds the moifture of the air. When a folution of gold 
is diftilled, a beautiful red liquor is obtained, which is 
found to confild of the muriatic acid, charged with a fmall 
portion of gold. The alchemifts, whole labours with gold 
were immenfely great, gave the name of the red lien to 
this liquor. Some cryftals of gold, of a reddilh yellow 
colour, are likewile lublimed In this procels; but the 
greateil part of the metal remains at the bottom of the 
retort, and requires only to be fufed, in order to regain 
all its properties. According to Vauquelin, the chromo- 
muriatic acid has the property of dillolving gold. 
The folution of gold is decompofed by a great number 
of intermediums. Lime and magnefia precipitate gold 
in the form of a yellowilh powder, which becomes darker 
by expofure to the air. Alkalis decompole the muriat of 
gold, forming triple falts. Fixed alkalis exhibit the fame 
phenomenon; but it muft be obferved, that the precipi¬ 
tate is afforded very llowly, and that the folution affumes 
a reddilh colour, if more alkali be added than is necel- 
fary; becaufe the excels of this lalt re-diffolves the pre¬ 
cipitated gold. The precipitate of gold may be reduced 
by heat alone, in doled velfels, this oxyd readily fuller¬ 
ing the oxygen to become difengaged in the form of vital 
air. It is, neverthelefs, capable of being fufed with vi¬ 
treous matters, and communicating a purple colour to 
them; for the precipitate of gold, formed by the mix¬ 
ture of a folution of gold and the liquor of Hints, is ufed 
in enamels and porcelain. Gold precipitated by fixed 
alkalis has likewife a property very different from that 
of gold in its. metallic ftate; it is foiuble in the pure ful¬ 
phuric, nitric, and muriatic, acids ; all thefe acids, heat¬ 
ed on the yellowilh precipitate of gold, readily diffolve 
