Metals. MINER 
foda is added, for the purpofe of forming a triple fait with 
the palladium, which is foluble in alcohol. The folution, 
with the common lalt added, is now to be evaporated to 
dry nets with moderate heat. This refiduum H next to 
be walhed with repeated additions of alcohol, till the li¬ 
quor becomes colourlefs. The triple muriat of foda and 
palladium, and the fame of platinum, if that metal be 
prelent, are diffolved in the alcohol. The Jubilance which 
the alcohol leaves undiffolved is of a deep red colour, and 
contains the rhodium in the date of triple muriat of ioda 
and the latter metal. If the alcoholic folution ilill con¬ 
tains platinum, it may be feparated by muriat of ammonia. 
To the remaining folution now add prufiiat.ol potaih, 
which caufes an orange precipitate. This being wailied 
and expofed to a tolerable heat, lofes its water, and the 
acid aflumes a grey metallic appearance. This fubitance 
is laltly to be heated with fulphur and borat in a cru¬ 
cible, when it will afford a metallic button which is pure 
palladium. 
This metal is of a white colour, more of the appear¬ 
ance of platinum than any other metal. It is fomething 
harder than the above metal, being about the lliffnefs of 
jewellers’ gold. It is lefs malleable than filver or plati¬ 
num, owing probably to its greater hardnefs. Its fpecific 
gravity, according to Dr. Wollalton, varies from 11;3 to 
ji-8. When heated to about 30 0 of Wedgewood, it af- 
fiunes a blue colour, owing to its combination with oxy¬ 
gen, in which property it has ibme refemblance to iron. 
If, however, the heat be increafed, the oxygen flies off, 
and it re-affumes its original luftre. It does not fufe at 
the ordinary temperature of furnaces. Although its oxyd 
feems to be formed at a certain temperature in the open 
air, it has not been procured by thefe means. An orange 
oxyd is procured by precipitation from the acids, but not 
fufficiently pure to get the proportion of oxygen ; hence 
we are at prelent unacquainted with the oxyds of palla¬ 
dium. It does not combine with carbon, nor is it known 
to combine with hydrogen, nitrogen, or phofphorus. It 
combines with fulphur, forming a compound, fuiible. at 
a low red heat. The fulphur gradually efcapes, leaving 
the metal in a flate of purity. . . 
According to the experiments of Chevemx, it forms an 
alloy with gold of a grey colour ; lefs duftiie than either 
of the metals. Its fracture was cryltallized. Its fpecific 
o-ravity, 11-079. It forms an alloy with platinum in equal 
parts. The alloy is as fuiible as palladium. It is lefs 
malleable than that with gold. Its fpecific gravity was 
15-141. It forms an alloy with an equal part of filver, 
much harder than the latter metal, and whiter than pla¬ 
tinum. Its fpecific gravity was n'z. Its''hlloy with lead 
is very fuiible, hard, and extremely brittle: its fpecific 
gravity was 12. Equal parts of copper and this metal 
form an alloy of a yellow colour, harder than wrought 
iron: its fpecific gravity was 10 - 392 . 
The oxyd of palladium combines with the acids, form- 
ino- faline compounds which have not been much at¬ 
tended to. The fulphuric, nitric, and muriatic, acids, 
when boiled upon palladium, oxydate and dilfolve it; but 
the nitro-muriatic acid afits upon it with the greatell 
energy : all the folutions are of a red colour. The oxyd 
is not precipitated from thele folutions in a flate of purity 
by the earths and alkalies, owing to its forming infoluble 
triple falts with molt of thole laline bales. T. he weight 
of the atom of palladium is not yet known with precifion. 
Sir Humphrey Davy lias flated it to be about 17 times the 
weight of the atom of oxygen. 
Rhodium. —This new metal, found in crude platinum, 
was fo called from the role-colour of a dilute folution of 
the lalts containing it, by Dr. Wollalton, to vvliofe in¬ 
quiries we are indebted for proof of its exiflence, and an 
account of its properties. 
This metal is thus procured : Some crude platinum 
being digelted in moderately-dilute nitro-muriatic acid, 
a brownilh-red folution is obtained. From this the pla¬ 
tinum is to be feparated, for the moil part, by muriat of 
A L O G Y. Metals. 507 
ammonia, and the refidual liquor is to be heated with 
zink; by this treatment a black powder will be obtained, 
and the fupernatant fluid will confifl of the muriats of 
zink and iron. This.black powder, by cligeflion in very • 
dilute nitric acid, will be freed from the copper and lead 
which it ufually contains, and the refidueisto lie digefled 
in dilute nitro-muriatic acid, till every thing foluble is 
taken up. To this folution a little common lalt is to be 
added, and the whole evaporated todrynefs; after which, 
by repeatedly waffling with warm alcohol, the foda-mu- 
riats of platinum and palladium will be diffolved, leaving 
behind a pure foda-muriat of rhodium. This fait is rea¬ 
dily foluble in hot-water, and depofits on cooling rhoni- 
boidal cryflals of a bright rofe-colour. Sal ammoniac oc- 
calions no turbidnefs in the folution ; but, if a few drops 
of muriat of platinum are added to the mixture, an im¬ 
mediate yellow precipitate is thrown down. Neither pruf- 
fiat of potaih, nor hydro-fulphuret of ammonia, nor the 
carbonated alkalies, produce any precipitate ; but the 
pure alkalies throw down a yellow oxyd, foluble either in 
alkalies or acids. The muriat of this metal is an uncryf- 
tallizabie fait of a rofe-colour, and foluble in alcohol ; 
with nitre, or the muriats of ammonia or foda, are formed 
cryflallizable triple falts infoluble in alcohol. Nitrat of 
rhodium is alfo uncryftallizable. It appears not to be de- 
compofable by filver ; but is fo by copper, mercury, and 
molt of the other metals. 
The foda-muriat of this metal affords a black powder 
by digellion with zink ; which, w-hen heated with borax, 
acquires a white metallic lullre, but is infulible by any 
heat that has hitherto been applied. It is, however, fu- 
fible either with arfenic or fulphur, and may be again fe¬ 
parated from thofe fubllances by heat; but it does not ac¬ 
quire by' this treatment any degree of malleability. It 
combines with mod metals; and with filver and gold forms 
very malleable alloys, which are unaltered by a high heat, 
but become encrufled with a black oxyd when llowly 
cooled ; an alloy of fix parts of gold and one of rhodium 
differs but little in colour from fine gold, but is much 
more difficultly fuiible. The fpecific gravity of rhodium 
appears to be fomewhat more than xi. That of an alloy 
confining of one part rhodium and about two parts -lead, 
was 11-3 ; which is lo nearly that of lead itfelf, that each 
part of this compound may be confidered as having about 
the fame fpecific gravity. The atom of rhodium is Hated 
by Berzelius to weigh 14-903. 
Iridium. —This metal was difcovered by Mr. Smithfon 
Tennant in 1803, and an account of it was publifhed in the 
Phil. Tranf. for 1804. It appears that, previous to its 
publication, the fame difcovery was made, to a certain 
degree, by Defcotils, which was afterwards taken up and 
enlarged upon by Fourcroy and Vauquelin. 
Mr. Tennant found that the fmall black fcales exilting 
in crude platinum, and which are left after the platinum 
has been diffolved, contained two metals which had not 
been previoufly noticed. (See p. 479.) He fubjefiled the 
above fubitance to the alternate afilion of potaih and 
muriatic acid, by which means he obtained two folu¬ 
tions. The black fcales were heated to rednefs in a fil¬ 
ver crucible, with their own weight of potaih. When the 
heated mafs has water added to it, the. potaih diffolves in 
combination with one of the metals, the folution being of 
an orange-colour. The refiduum being treated with mu¬ 
riatic acid, a folution was obtained, which at firlt was 
blue, then became olive-green, and ultimately of a red 
colour, confilling of the acid united to the oxyd of the 
other metal. By this alternate treatment, the oxyd of 
ofmium, tlte other metal alluded to, was diffolved in the 
potaih, and the oxyd of iridium in the muriatic acid. The 
acid folution, on being evaporated to drynefs, afforded cry f- 
tals of an ofitohedral form, which was, no doubt, a pure 
muriat of iridium. The folution of thefe cryftals is of a 
deep red colour. When a plate of zink, or any other me¬ 
tal having a greater affinity for oxygen than itfelf, is 
placed in the iblution, a black powder is precipitated, 
which. 
