CHEMISTRY. 
316 
it, but do not become fufliciently faturated to afford 
cryftals. 
Ammoniac precipitates the folution of gold in much 
greater abundance. This precipitate, which is of a brown 
yellow, and fometimes of an orange colour, has the pro¬ 
perty of detonating with a considerable.noife when gently 
heated: it is called fulminating gold. The ammoniac is 
abfolutely necelfary in the produftion of fulminating 
gold ; this preparation may be formed either by precipi¬ 
tating a folution of gold in nitro-muriatic acid, made 
with ammoniacal muriat, by the addition of fixed alkali, 
or by precipitating with ammoniac a folution of gold, 
made in aqua regia, compofed of pure nitric and muri¬ 
atic acids. The fulminating gold always weighs one- 
fourth more than the gold dilfolved in aqua regia. Tiie 
terrible elfefts of fulminating gold render it neceffary, to. 
aft with great caution in the management of this fubjeft ; 
it mull be carefully dried in the open air, without being 
brought near the fire, as a ftrong heat is not neceffary to 
produce the fulmination, and friftion alone is fufficient 
for this purpofe: the veffels which contain it ought net 
to be clofed with glafs Hoppers, but with cork; the moft 
dreadful accident's have fhewn, that glafs Hoppers, by the 
friftion they produce in the necks of the veffels, expofe 
the operator to great danger, from the fulmination of 
fuch particles of gold as may remain between the Hopper 
and the neck. If a very fmall quantity of this fulmi¬ 
nating gold be put on the blade of a knife, and gently 
heated, it catches fire, and gives a violent explofion. 
The oxygen of the oxyd of gold feizes on the hydrogen, 
and forms water, which, driven up fuddenly in vapour,occa- 
fions the explofion ; the azot is difengaged, and the gold 
remains prrre; it is found incruHed on the blade of the 
knife. Berthollet has proved, that, by dilciiling this fait 
in metal tubes, azot is produced, and the gold was re¬ 
duced to its metallic Hate. To deprive it of its fulmi¬ 
nating property, Darcet put fome to foak in oil, and 
then heated it in a crucible. It is foluble in an excefs 
of alkali. 
Gold is precipitated from its folutions by all bodies 
which have more affinities with oxygen than gold has. 
With fulphureous acid, fulphuric acid is formed, and 
the gold is precipitated. We mufi here obferve, that 
gold, precipitated from its folution by any intermedium 
whatfoever, is perfectly pure, even more fo than gold 
purified by the procefs of parting ; becaufe it is feparated 
from the filver it may contain in this lafi procefs, which 
may fall down in the form of a muriat, and takes place 
even during the folution of gold, as we have before re¬ 
marked. 
A plate of tin, plunged in a folution of gold, fepa- 
rates the gold in the form of a deep violet powder, called 
purple precipitate of Cajfms. This precipitate, wh cli is 
ufed in painting in enamel and on porcelain, is prepared 
by diluting a folution of tin in nitro-muriatic acid, with 
a. large quantity of uiftilled water, and pouring in a few 
drops of the folution of gokl; when the folutions are 
well faturated, a red or crimfon precipitate is imme¬ 
diately formed, which at the end of a few days becomes 
purple: this precipitate is light, land, as it were, mucila¬ 
ginous; it is'feparated from the liquor by filtration, 
waflied, and afterwards dried. The experiments of Pel¬ 
letier have proved why the precipitation of gold does 
not take place with the oxygenated muriat of tin. 
Lead, iron, copper, and filver, have likewife the pro¬ 
perty of feparating gold from its folvent; lead and filver 
precipitate it of a deep and dirty purple ; copper and iron 
leparate it with its metallic brilliancy. Alcohol, acetit 
of copper, and green fulphat of iron, precipitate the fo¬ 
lution of gold, becaufe thofe fubfiances are fufceptible of 
uniting to a greater quantity of oxygen, and they feize 
on that whicli was united to the gold, and by means of 
which it was held in folution. But the iuper-oxygenated 
oxyd of iron cauies no precipitate, the reafon of which 
mufi be apparent from what has been faid above. 
Sulphuric ether is another means of recovering gold 
from its nitro-murihtic folution; thus general Lamotte 
prepared his drops. A-folution of gold applied to bones, 
ivory, feathers, and vegetable matters, as linen, &c. 
leaves a purple-red fpot not to be effaced ; on the fkin it 
will leave purple fpots, which lafi feveral days; they 
turn, by degrees, brown, and almofi black. 
The name of gold in rags, is given to the following 
preparation: Very fine clean rags are fleeped in a folu- 
tion of gold, and afterwards dried and burnt in a cruci¬ 
ble : the afiies, which are of a dark purple colour, are 
ufed to gild fmall pieces of copper and filver; it is gene¬ 
rally rubbed on with a bit of cork, and the gold, being 
fo minutely divided, eafily adheres. 
Gold is applied to a great number of ufes; its fcarcity 
and price in a great meafure prevent its being made into 
utenfils or veflels; but, as its brilliancy and colour are 
very agreeable, methods have been found of applying it 
to the fur face of a great number of bodies, wlfi-ch it at 
the fame time defends from the impreffions of the air. 
This art, in general called gilding, is performed in a va¬ 
riety of methods. , Leaves of gold are often applied on 
wood by means of fome glutinous fubfiance. A powder 
of gold is prepared by triturating the clippings of gold 
leaf with honey, walking the pafie with water, and dry¬ 
ing the particles of gold which precipitate. Shell-gold 
is an oxyd of gold, mixed with a mucilaginous water, or 
folution of gum. Water-gilding is done by previoufly 
cleaning a piece of copper, intended to be gilt, with fand 
and weak aqua-fortis, called aqua fecunda, after which 
the piece is plunged in a diluted folution of mercury; 
the mercury which precipitates caul'es the amalgam of 
gold to adhere, which is fpread on the piece, after hav¬ 
ing w.ifhed it with water to carry off the acid ; when the 
amalgam is uniformly fpread, the piece is heated on 
charcoal, to volatilize the mercury, and the work is 
finilhed by covering it with gilder’s wax, compofed of red- 
bole, verdegris, alum, or martial vitriol, incorporated 
with yellow wax, and heated once more to burn oft’ the 
wax. The other ules of gold, for toys, laces, See. are 
fufliciently known without enumeration. As to the me¬ 
dicinal virtues attributed to gold, it is admitted, by all 
phyficians of reputation, that they are imaginary, and 
that the effefts of the different kinds of potable gold pro- 
pofed by the alchemifts, arile from the fubfiances in which 
the metal has been mixed or dilfolved. 
Of PLATINA. 
Platina, which has not been known as a peculiar metal 
above half a century, has been hitherto found only in 
the gold mines of America, more efpecially in thofe of 
Santa Fe near Carthagena, and in the bailiwick of Choco 
in Peru. The Spaniards give it this name from the word 
plata, which fignifies filver in their language, by way of 
companion to that metal, whofe colour it imitates. The 
name of white gold, however, appears to agree better with 
its properties than that of little filver, becaule it in Lift 
refembles gold much more than liiver in moft of its. pro¬ 
perties. Some toys made of platina were in exiftence 
before the time we have cited ; but, as this metal cannot 
be melted and wrought alone, it is probabie that the 
fnuft-boxes, heads of canes, and other uteniiis of this 
kind, which were fold under the name of platina, were 
ailoys of this metal, with certain metallic fubfiances, 
which might give it fufibiiity. The platina, in minera- 
logical collections, has the form of fmall grains, its plates 
of a bluifh black, whofe colour is intermediate between 
thofe of filver and iron. Thefe grains are mixed with 
many foreign fubfiances; they contain 1 until particles of 
gold, blackilh ferruginous fandy grains, which by the 
magnifier appear fcorified, and certain particles ot mer¬ 
cury. If the grains of platina be examined under the 
magnifier, Tome appear angular, others round and flat, 
like a kind of button. When beat on the anvil, moft of 
them are flattened, and appear duftile; fome break into 
feveral 
