C H E M 
■nitric acid will take a blue or red tinge, (hewing tliat it 
contains copper. It is neceflary allb to examine the pu¬ 
rity of the nitric acid ; for, if it contains fulphuric or 
muriatic acid, a white precipitate, tiioreorlef’s abundant, 
will be formed. A large matrafs fhould be ufed, for the 
adtion of the nitric acid upon the filver is very ftrcng 
and rapid; and a large quantity of nitrous gas is difcii- 
gaged, even without the afiiltance ol heat. This folution 
is exceedingly caullic, tinges the epidermis of a black 
colour, and entirely corrodes it. When highly charged 
with the metal, it depofits fender brilliant cryitals, re- 
fembling thofe of boracic acid; when half evaporated, 
it affords, by cooling, fiat cryftals, which are either hex- 
.agonal, or triangular, or. fquare, and appear to be form¬ 
ed of a great number of ffriall needles, placed one befide 
the other. Thef'e are called the nltxal of fiver, or lunar 
ayfals. The fait is quickly altered' by the contaft of 
light, and blackened by combuftible vapours. It deto¬ 
nates on heated charcoal, and leaves a white powder, 
which is pure (liver. It is very fufible : if it be expofed 
to heat in a crucible, it firfl: fwells up and lofes the water 
of cryftallization, after which it remains in fufibn ; and, 
if fuffered to cool in this ftate, it appears to be a grey 
mafs, and forms a preparation known in pharmacy and 
furgery by the name of lapis infernalis. It is not necef- 
fary in making this preparation to ufs the cryftallized ni¬ 
trat of filver, which is difficult and expenfive to obtain; 
as it is fufficient to evaporate a folution of filver in the 
nitric acid to drynefs, and to put this refidue in a cruci¬ 
ble or filver ladle, as Baume advifes, and to heat it flovt- 
■ 3 y tiil it is in an undifturbed fufion, in which ftate it mult 
be poured into a mould, to give it the form of final) cy¬ 
linders. If the cylinders of lapis infernalis be broken, 
they are found to be of a needle-formed texture, radiat¬ 
ing from the'axis of each cylinder. Nitrat of filvet mult 
not be too long heated to make the lapis infernalis, as 
by that means a part of the fait would be decompofed, 
and a button of filver would be found at the bottom of 
the crucible. To afcertain what pafles in this operation, 
Fourcroy diftilled this fait in the pneumatic apparatus; 
they afforded nitrous gas, and vital air, mixed with a 
fmali quantity of azotic gas ; the filver was recovered in 
the matrafs, entirely reduced. The glafs was opake like 
enamel, and of a beautiful ma'rron brown colour. Nitrat 
of lilver, expofed to the air, does not attract moifture; 
it is very foluble in water, and may be difl'olved by twice 
its weight of cold water, but boiling water will diflolve 
almoft its own weight. 
Take filver of twelve carats fine, diflolve it in very 
pure nitric acid, and then precipitate it by lime in the 
oxyd ftate; (train, and dry the precipitate with a gentle 
heat, or in the fun. Pour ammoniac over this dried oxyd 
of filver, and by fpontaneous evaporation you ha ve ful¬ 
minating fil-ver, or anunoniacal oxyd of fiver. Great care 
mull be taken in the preparation of this oxyd, for it de¬ 
tonates with extreme facility, owing to the decompofition 
of the ammoniac ahd the oxyd; for the hydrogen of the 
ammoniac combines with the oxygen of the oxyd, and 
the azot is di fen gaged. We are indebted to Berthollet 
for this experiment. 
Put a folution of filver in nitric acid into a gbfs; drop 
in fome fulphuric acid, and a white pulverulent precipi¬ 
tate is produced immediately; this is fulphat of filver. 
The fame decompofition takes place with any other ful- 
phat. In this cale there are two decompofitions, and two 
frefh combinations : the nitric acid, feparated from the 
filver, unites with the bafe oft the fulphuric falts. The 
muriatic acid, and its combinations, prefent the lame 
phenomena. If a hydro-fulphure be poured into a folu¬ 
tion of nitrat of lilver, the lilver is precipitated black. 
Moll metallic matters are capable of decompofing the 
nitric folution of filver, becaule they have a (tronger affi¬ 
nity than that metal with oxygen. The arfeniat of pot- 
alh, difl'olved in water, produces a reddilh precipitate in 
the nitric folution, which confifts of filver united with 
: S T R Y. 3 it 
arfenic acid; this precipitate relembles the red ore of lil¬ 
ver; but, if the folution of filver is not perfectly faty- 
rated, the precipitation does not take place. Silver.may 
be precipitated in its metallic ftate by molt metals ; but 
we {hall more particularly attend to the feparation of this 
metal by mercury or by copper, becaufe of the pheno¬ 
mena the firll prefents, and the utility of the latter. 
Silver feparated from the nitric acid by mercury is int 
its metallic ftate, and the flowmefs of its precipitation 
produces a peculiar fymmetrical arrangement, known by 
the name of Arbor Diana, or the philofdphical tree. There 
are many procefies for obtaining this cryftallization. Le- 
mery diredls one ounce of fine filver to be difl'olved in 
nitric acid of moderate ftrength : this folution is to be 
diluted with about twenty ounces of diftilled water, and 
two ounces of mercury are to be added : in forty days a 
very beautiful vegetation is formed. Homberg has pre- 
fcribed a much lhorter procefs : according to this chemift, 
an amalgam of four drachms of leaf filver, with two 
drachms of mercury, mull be made in the cold, this 
amalgam is to be difl'olved in a fufficient quantity of ni¬ 
tric acid, and a pound and a half of diftilled water muft 
be added to the folution. A little ball of the foft amal¬ 
gam of filver mull be put into an ounce of this liquid, 
and the precipitation takes place almoft inftantly. The 
precipitated filver, united to a portion of the mercury, 
difpofes itfelf in fibres of a prifmatic appearance on the 
furface of the amalgam : other fibres appear and infert 
themfelves in the foregoing, fo as to exhibit a vegetation 
in the form of a bufh. Lal'tly, Baume has defcribed a 
method cf obtaining the arbor Dianoe, which differs in 
fome refpedts from that of Homberg, and fucceeds with 
greater certainty; he directs fix drachms of the folution 
of filver, and four of the folution of mercury, in the 
nitric acid, both well faturated, to be mixed, and five 
ounces of diftilled water to be added to thisriiquor. The 
mixture muft be poured into an earthen veil'd,-upon fix 
drachms of an amalgam of filver, made with feven parts 
of mercury and one part of filver. Thef'e two methods 
fucceed much more quickly than that of Lemery, by the 
reciprocal adtion and affinity between the metallic fub- 
ftances. In fad, the mercury contained in the folution 
attracts that of the amalgam ; the filver contained in the 
latter adts likewife on that which is held in folution, and 
from thef'e attractions a quicker precipitation of the filver 
takes place. The mercury, which compof’es a part of 
the amalgam, being more abundant than is neceflary to 
precipitate the filver from the folution, produces likewife 
; a third eft'edt of confiderable importance ; it attradls the 
filver by the affinity and tendency it has to combine with 
that metal, and it eft'edtually combines with it; fince the 
vegetations of the arbor Diante are a true bi ittle amalgam 
of a cryftallized form. This cryftallization fucceeds' 
much better in conical veffels, or glafles, than in round 
or open veffels, fuch as the cucurbit recommended by 
Baume. It may likewife be obferved, that it is neceflary 
to place the veil'd in which the experiment is made, in 
a fituarion where it may not be lhaken, or agitated, as 
i'uch circuiriflances would effedhially prevent the fymetri- 
cal arrangement of the cryftallization. 
Copper plunged in the folution of filver, precipitates 
this metal likewife in a brilliant and metallic form. This 
procefs is ufually employed to feparate the filver from its 
folvent, after the procefs of parting. Plates of copper 
are immerfed in the folution, or the folution itfelf is 
oured into a vefftel of copper; the filver immediately 
ecomes feparated in wbitifli grey flocks. When the li¬ 
quor becomes blue, and is deprived of all its filver, it 
is decanted off; the filver, after being wafhed feveral 
times in water, is melted in a crucible and cuppelled, in 
order to feparate it from the portion of copper with which 
it united during the feparation. The filver afforded by 
this operation is the pureift of all; it is twelve penny¬ 
weights fine. From thef'e two precipitations of filver by 
mercury and copper, we fee, that metals feparated from 
their 
