2 'jo CHEMISTRY. 
of iron, brittle, which being broken exhibits a foliaceous 
texture like fern-leaves, of an iron-grey colour, without 
much metallic brilliancy. The fpecific gravity of this 
very pure cobalt, according tb Hauy, is 8-5384; and this 
metal, though entirely deprived of iron, is ftill ftrongly 
attracted by the magnet. As this gentleman has not let 
down the other charafferiftics of this metal thus purified, 
our following remarks mull be taken to refer tb cobalt 
procured by the ufual methods. 
In the arts, and in the large works, cobalt is not ex¬ 
tracted in the metallic form : after pounding and walking 
the cobalt ore, it is roafted in a furnace, which terminates 
in a long horizontal flue, that ferves inftead of a chimney. 
In this flue, the oxyd of arfenic, being fubiimed, becomes 
condenled into the iemi-vitrified fubilance, which is im¬ 
properly called white arfenic. If the ore contain bifmuth, 
this very fufible metal is collected at the bottom of the 
furnace ; the cobalt remains in the Hate of an obfcure 
grey oxyd, called zaffre. The zalire, in commerce, is 
never pure, but is mixed with three times its weight of 
pulverifed flints. In this ftate, if it be expofed to a flxong 
Are, it melts into a glafs, of a dark blue colour, called 
fmalt. This is reduced to powder in mills, and mixed with 
watej\ The firft portion which falls down is the largeft 
grained, and is called coarfe fmalt ; the turbid water being 
decanted off, affords a fecond precipitate; and this de¬ 
cantation is repeated four times in the whole: the laft de- 
polition, which is finer than the reft, is improperly called 
azure of four fires. This azure is ufed in many arts to 
give a blue colour to metals, glaffes, See. 
The zaft're of commerce, fufed with three times its 
weight of black flux, a fmall quantity of tallow and ma¬ 
rine l'alt, affords the femi-metal, known by the improper 
name of regulus of cohalt. The reduCtion of zaffre is 
very difficult. A large quantity of flux mult be ufed, 
and the crucible muft be kept a confiderable time in a 
white-red heat, that the matter may become very fluid, 
and that the fcoria may be completely fufed into a blue 
glafs ; at this period the cobalt links to the bottom, in 
the form of a button ; this is what modern chemifts call 
metallic cobalt. 
Cobalt, expofed to heat, does not melt till it is well 
ignited. This metal appears to be very fixed in the 
fire, and it is not know-11 whether it can be volatilized 
in clofe vefl’els. If it be fulfered to cool flowly, it cry- 
ftallizes in needle-formed plifms, placed one on the 
other, and united in bundles. It confiderably refembles 
mafles of bafaltes, which are feparated from each other, 
as Mongez obferves. To fucceed in this cryrtallization, 
the cobalt muft be melted in a crucible till it appears to 
boil ; and, when the furface of the femi-metal becomes 
fixed, on withdraw-ing it from the fire, the veffel is to be 
inclined. The metal, which ftill remains fluid, runs out 5 
and that portion which adheres to the fides of the kind 
of geodes, formed by the cooling of the furface of the 
cobalt, is found to be covered with cryftals. 
Cobalt, melted and expofed to the air, becomes cover¬ 
ed with a dull pellicle, which is an oxyd of the femi- 
metal, formed by its combination with oxygen. A larger 
quantity of the oxyd of cobalt may be more eafily had, 
by expoling the pulverized femi-metal, in a fhallow veffel, 
under the muffle of a cuppelling furnace, and ftirring it 
up, from time to time, to renew the calcining furface. 
This powder, after remaining ignited forfome time, lofes 
its brilliancy, increafes in weight, and becomes black. 
This black oxyd requires a molt violent heat to convert 
it into glafs, which is then of a deep blue colour. 
Cobalt becomes flightly tarnifhed by expofure to air, 
and is not attacked by water. It does not unite with ful- 
phur without difficulty ; but, with the addition of an 
alkali the combination is very ftrong, fo that they cannot 
be feparated without folution in acids. For this purpofe 
melt in a crucible equal parts of the calcined ore of co¬ 
balt, potafh, fulphat of lime,' and rofin ; when the mix¬ 
ture is melted, let it grow cold, and a confiderable quan¬ 
tity of cobalt will be found combined with the fulphure 
formed during the operation; this combination generally 
fwims above the fcoria; the remainder, collected at the 
bottom of the crucible, feetns compofed of feveral me¬ 
tallic fubftances feparated from the cobalt. This fulphu- 
rated cobalt diflolves eafily in nitric acid, and throws 
down a w'hite powder containing fulphur, and fome other 
metallic fubftances. 
To obtain phofphorated cobalt, melt a mixture of one 
part of phofphorated glafs, one part of metallic cobalt 
in powder, and one-eighth part of charcoal. The pro¬ 
duct of this fufion is a layer of phofphdrated cobalt covered 
with a beautiful blue glafs. This phofphonuion may be 
produced by making cobalt red-hot in a crucible, and 
throwing in little bits of phofphorus up to the point of 
faturation. Phofphorated cobalt differs from common 
cobalt in colour; it is white, more inclined to blue ; it 
is brittle, and in, breaking thews a cryftalline form. It 
lofes its brightnefs. Under the blow-pipe, the phofpho¬ 
rus burns on the furface, and the refldue is a fmall vitreous 
globule of a dark blue colour. 
The aCtion of barytes, magnefia, and lime, on cobalt, 
is not known. Alkalis diflolved in water manifeftly alter 
it; but thefe changes have not been accurately deferib- 
ed. This metal diflolves in all the acids, but with dif¬ 
ferent phenomena, according to its own ftate and that of 
the acid. It is not foiuble in fulphuric acid, unlefs it be 
concentrated and boiled. This folution is made in a 
glafs phial or retort; putting in one part of cobalt in 
powder, and pouring over it three parts of concentric 
fulphuric acid. Place the retort in a fand-bath, fit on a 
receiver, and proceed to diftillation, firft with a gentle 
fire, which is to be increaled by degrees till the acid 
boils; a quantity of fulphurous gas pafles over. When 
the acid is almoft entirely evaporated, the refidue muft 
be waffled ; a portion diflolves in the water, and commu¬ 
nicates a rofy or greenilh colour; it is the fulphat of co¬ 
balt. The other part coniifts of cobalt, oxydated by the 
acid, wliofe oxygen has combined with the metal. Beaume 
affirms, that by fufficiently evaporating the fulphuric fo¬ 
lution of cobalt, two forts of cryftals are obtained by 
cooling; the one white, fmall, and cubical; the other 
greenifh, quadrangular, fix lines in length, and- four in 
breadth. He conliders thefe laft as the fulphat of cobalt. 
The former are produced by certain foreign matters 
united to the cobalt. The cryftals of the fulphat of co¬ 
balt moll commonly obtained have the form of fmall 
needles, deferibed by Sage as tetrahedral-rhomboidal 
prifms, terminated by a dihedral fummit, with rhombic 
faces. They are decompofable by fire, and leave an oxyd 
of cobalt, not reducible alone. Barytes, magnefia, lime, 
and the three alkalis, likewife decompofe this fait, and 
precipitate a rofe-coloured oxyd of cobalt. 
This fait attracts the moifture of the air; and is de- 
compofed by heat. Nitric acid diflolves it with the af- 
fiftance of caloric : Put cobalt in powder into a matrafs ; 
pour over it five or fix times its weight of nitric acid at 
40 0 ; place the matrafs on a fand-bath, and heat it till 
the cobalt is diflolved; let the folution ftand to fettle, 
then draw it off 5 the folution, when at the point of fa¬ 
turation, will be of a rofy brown, or elfe a bright 
green. Evaporate this folution over a fand-heat to one- 
half ; in cooling, it furnilhes cryftals in fmall-conneCted 
needles : this is nitrat of cobalt. This fait is very deli- 
quefeent, boils up on hot coals, without detonating, and 
leaves a deep red oxyd. It is decompofed by the fame 
faline intermediums as the fulphat of cobalt. If more 
alkali be added in thefe decompofitions than is neceffary 
to precipitate the oxyd of cobalt, the precipitate difap- 
pears, by folution in the excefs of alkali. 
The muriatic acid does not diffolve cobalt in the cold, 
but takes up a portion by the afliftance of heat*. This 
acid aCts more ftrongly on the oxyd, forming a fo¬ 
lution of a red brown, which becomes green when heat¬ 
ed. By evaporation, it affords a muriat of cohalt cryl- 
tallized 
