308 Metals. MINERALOGY. Metals. 
which, on being heated, becomes white, and acquires me¬ 
tallic luftre. This metal, like gold and platinum, has fo 
little attraction for oxygen, that it may be obtained by 
expofing the cryftals of its muriat to a ftrong heat. In 
this ftate it is deemed pure iridium. It is a white metal, 
having the appearance of platinum. Owing to its great 
infufibility, we are not acquainted with fome of its phyfi- 
cal properties, fuch as its malleability, See. It had not 
been fufed by Mr. Tennant nor the French chemills. It 
has, however, fince been made to affume the liquid form, 
by means of the very intenfe heat produced by the large 
galvanic battery lately exhibited at the Royal Inftitution 
by Dr. Davy. This heat was fo great, that at the fame 
time the earths alumine and zirconia were fufed, and 
charcoal was volatilized. 
Iridium forms malleable alloys with feveral of the me¬ 
tals, a prefumptive proof that it is itfelf malleable. Mr. 
Tennant found that it did not combine with arfenic, but 
that it eafily united with lead ; from which, like the no¬ 
ble metals, it may be feparated by cupellation. It forms 
malleable alloys with copper and filver. Its alloy, with 
gold, differs little from pure gold, even when the iridium 
is in coniiderable quantity. It appears to Hand next 
above gold and platinum in its affinity for oxygen. It 
may be inferred, from the change of colour in the acid fo- 
lution, that it admits of at leall two ftages of oxydation. 
When the metal is in its pure ftate, it is not aCted upon 
by any acid except the nitro-muriatic ; and even this acid, 
according to Fourcroy and Vauquelin, diffolves only 
? i_th of its weight. Its combinations with the other acids, 
and with combuftible bodies, have not been attended to. 
Specific gravity, 19MJ. 
Osmium. —We have juft noticed, that, when the black 
powder, which remains after difi'olving platinum from the 
grains as they come from South America, is alternately 
treated with an alkali and an acid, two folutions are ob¬ 
tained. The acid folution contains the iridium, while 
the alkali contains the metal called ofmium. For the 
difeovery of this metal we are indebted to Mr. Tennant. 
Fourcroy and Vauquelin had previoufly made fome expe¬ 
riments upon the black powder above alluded to; but it 
feems they had confounded the two metals which it af¬ 
forded. 
The alkaline folution from the black powder contains 
the oxyd of ofmium, to which it gives a yellow colour. 
In order to obtain the oxyd pure, the alkaline folution 
muft be put into a retort. When fulphuric acid is added, 
and heat applied, the oxyd comes over, diffolved in water, 
to which it gives a ftrong fmell and a fweetiffi tafte. If 
the black powder be heated with nitre in a retort, at a 
temperature a little fhort of rednefs, the oxyd of ofmium 
rifes and condenfes in the neck of the retort, in the form 
of oil. On cooling, it concretes into a femi-tranfparent 
mafs. This tiibftance is foiuble in water, and polfeffes 
fimilar properties to that obtained from the alkaline folu¬ 
tion. It holds its oxygen with fo little affinity, that, if 
mercury be ffiaken with either the alkaline or the aqueous 
folution, the metal is fet free, and forms an amalgam with 
the mercury. If the mercury be diftilled from the alloy 
without contact with the air, the ofmium remains in a 
ftate of purity. 
Ofmium is of a dark blue-grey colour, having metallic 
luftre. This laft property, together with its forming an 
ailoy with mercury, lufficiently prove its metallic nature ; 
and its fpecific gravity is 19'15. When heated in the 
open air, it appears to evaporate. It is not, however, the 
pure metal which evaporates; but this occurs in confie- 
quence. of its combining with the oxygen of the atmo- 
fphere, fince the metal is not volatile when .the oxygen is 
excluded. When it is heated ever fo ftrongly in a clofe 
crucible lined with charcoal, it does not fule. The moft 
remarkable property of this metal is its not being oxyd- 
ated by any of the acids, although it eafily combines with 
the oxygen of the atmofphere, and with that afifing from 
the decompofition of nitric, above ftated. It is not Id's 
curious that it ffiould be oxydated and diffolved by potaffi. 
Although the oxyd of this metal is foiuble in water, and 
its affinity for oxygen fmall, it does not change vegetable 
blues, nor exhibit any other acid properties. 
The folution of oxyd of ofmium, like that of gold and 
filver, ftains the {kin permanently. An infufion of galls 
changes it to a purple colour, which ultimately becomes 
blue. If ether or alcohol be added to the aqueous folu¬ 
tion, the oxyd is decompofed, and the metal precipitated : 
a fimilar effeCf would no doubt take place by palling hy¬ 
drogen or fulphuretted hydrogen gafes through the folu¬ 
tion. This oxyd is decompofed by all the metals except¬ 
ing gold and platinum. The other metals, being immerfed 
in the folution of this oxyd, foon deprive it of its fmell, 
while the ofmium is precipitated in the metallic form. 
We are indebted to Mr. Tennant for thefe obfervations, 
which he made out at the time he difeovered the metal. 
It is to be regretted tljat no new faCts have been added, 
by which we might know the proportion of its combina¬ 
tions with other bodies. 
Potassium and Sodium. —Thefe are the names of two 
new metals difeovered by the decompofition of potaffi and 
foda. This grand difeovery of the decompofition of al¬ 
kalies was made by Mr. (now Dr. Sir Humphrey) Davy, 
and firft explained by him in his LeCtures at the Royal 
Inftitution in June 180S. r 
Potafli and foda, in their dry ftate, are non-conduCtors, 
but, when moiftened, have the property of conducting 
electricity. In both inftances Mr. Davy clearly produced 
metalline fubftances, by bringing them within the aCtion. 
of the Voltaic battery. Oxygen was given out at the po- 
fitive fide of the battery, and at the negative little glo¬ 
bules of the metallic bafe were inftantly formed. The 
metalline bafes of the alkalies he named Potajjium and 
Sodium, choofing the termination um, in compliance with 
the prefent nomenclature of metals, in order that they 
might agree with Platimm, Plumb«»i, Sec. See. Thefe 
new metals, to appearance, are precifely like mercury, 
but very different from that metal in their various pro¬ 
perties. He ffiowed the great inflammability of the new 
metals, by touching them with the fmalleft quantity of 
water, when they inftantly took fire. They are both 
malleable at the common temperature, and may belpread 
into very thin leaves on a plate of glafs, by mere preffure. 
So great, however, is their attraction for the oxygen of the 
atmofphere, that they almoft inftantly become tarniflied. 
Before the difeovery of thefe new metals, only two bodies 
of this clafs, viz. iron and platinum, were capable of being 
welded, and that at a very great heat, whereas feparate 
parts of the potaffium and fodiurn can be united readily 
at the common temperature of the atmofphere. 
Mr. Davy’s brilliant difeovery was no {ooner known 
at Paris, than the French chemifts eagerly haftened to ex¬ 
plore the new track. The refearches of Meffieurs The- 
nard and Gay-Luffac (communicated to the National In- 
ftitute, and publifhed in the Mem. de la Soc. d’Arcueil 
in 1809) appear to have been conducted with uncommon 
ingenuity and luccefs. By fufing with intenfe heat, in a 
clean gun-barrel, the cauftic potaffi in contaCt with iron 
filings, and condenifng the fublimate by the application 
ofexceffive cold at the other extremity of the barrel, they 
procured a quantity of the fluid metal at a much lefs ex- 
penfe, and in far greater quantity, than can be obtained 
by the ordinary Galvanic procefs ; and thus they were 
enabled to examine the combinations of this new fub- 
ltance on a pretty large feale. The metal of foda was 
procured in a fimilar manner. And it was difeovered, 
that the aCtion of thefe metals, among other (hiking ef¬ 
fects, occafions the decompofition of ammoniac and of the 
acid of borax. 
Few difcoveries in modern times have fo powerfully ex¬ 
cited the attention of the lcientjfic world, as that of the 
metallic nature of potafli, foda, Sec. though this difeovery 
has not hitherto been attended with any beneficial prac¬ 
tical application. It can however fcarcely be doubted, 
. that 
