COB 
COB 
(composed of mail and plates) became com- 
mon, and tlie steel boddice was gilt and 
otherwise ornamented. I'his armour did 
not, however, long continue in fashion, but 
was succeeded by tabards of arms larger 
than the original surcoat, and made of the 
richest silk stuffs, sumptuously embroider- 
ed; which afterwards became the dress 
worn by the nobility and gentry, till the 
commencement of the sixteenth centui'y : 
since that time tltey have been continued 
only as the state dress of tlie otRcers of 
arms. 
Coats, in a ship, are pieces of tarred can- 
vass put about tlie masts at the partners 
to keep out water. They are also used at 
the rudder’s head, and about the pumps 
at the decks, that no water may go down 
there. 
COATING, in chemistry, is used prin- 
cipally for the purpose of defending certain 
vessels from the immediate action of fire ; 
thus, glass retorts, and the inside of some 
furnaces, are coated with various compo- 
sitions. 
Coating, in electricity, means the cover- 
ing of electric bodies with conductors, or 
the latter with the former, or, lastly, elec- 
trics with other electrics. Electrics are 
coated with conductors for the purpose of 
communicating to, or removing from their 
surfaces, the electric fluid in an easy and 
expeditious manner; otherwise an electric 
body, on account of its non-conducting 
property, cannot be electrified or deprived 
of the electric fluid without touching almost 
every point of its surface with an electrified 
or other body. This coating generally con- 
sists of tin- foil, sheet-lead, gilt paper, gold- 
leaf, silver leaf, or other metallic body, ei- 
ther in the form of a thin extended lamina, 
or in small grains, such as brass filings and 
leaden shot. The coating may be fasteneff'i 
to the surface of the electric by means of 
paste, glue, wax, or other adhesive matter. 
COBALT, in chemistry, a metal, when 
pure, of a white colour, inclining to bluish 
or steel grey. At the common tempera- 
ture its specific gravity is more tlian 8.5. 
It is attracted by the magnetic needle, and 
is itself capable of polarity. For fusion it re- 
quires nearly the same intensity of heat as 
cast iron. In a state of oxide, it tinges the 
saline Vitreous fluxes of a deep blue colour. 
It is soluble in nitro-rauriatic acid, and the di- 
luted solution forms a blue sympathetic ink. 
Cobalt occurs in nature alloyed with other 
metals, and mineralized by oxygen, and by 
arsenic acid. The white cobalt ore is an 
VOL. II. 
alloy of cobalt and arsenic, with a little 
sulphur, and in some specimens a little 
iron, the two latter being probably acci- 
dental. One variety, analyzed by Klap- 
roth, gave 44 of cobalt, 55.5 of arsenic,^ 
and 0.5 of sulphur. Its colour is tin-white, 
liable, however, to tarnish, and thus to as- 
sume a grey or reddish tinge ; its lustre is 
weakly shining and metallic. 
'J'he grey cobalt ore, as it has been 
named, is an alloy of cobalt with arsenic 
and iron ; sometimes, also, as has been af- 
firmed, with small portions of nickel and 
bismuth. Its colour is light grey, but very 
liable to tarnish ; its lustre weakly shining 
and metallic. Exposed to the flame of the 
blow-pipe, it gives an arsenical odour 
and smoke, but without melting : to borax 
it gives a blue colour, and is reduced to a 
metallic globule. The native oxide of co- 
balt occurs in a powdery form, or of va- 
rious degrees of induration, but always 
dull, and earthy in its fracture, soft, and 
easily broken. It is also of different co- 
lours, from the intermixture of oxide of 
iron, and perhaps other metallic oxides ; 
whence even species have been formed and 
distinguished by the names of black cobalt 
ochre, brown cobalt ochre, and yellow co- 
balt ochre. Of these the black appears to 
be the oxide of cobalt in its purest state. 
They all give a blue colour to glass, or to 
borax when fused with it by the blow-pipe. 
Sometimes also they exhale an arsenical 
odour. The last species is that in which co- 
balt is mineralized by arsenic acid, the 
principal variety of which has been named 
peach-bloom cobalt ore. This name it de- 
rives from its colour, which is a beautiful 
red, similar to that of the peach blossom, 
passing, however, into other shades of red, 
and from decomposition into other colours. 
The ores of cobalt are easily distinguished 
from all others, by their property of com- 
municating to boi-ax or to glass, when fused 
with them, a deep blue colour, and by their 
solution in nitro-muriatic acid being a sym- 
pathetic ink, lines traced with it on paper 
not being visible when cold, but becoming 
visible on exposure to a moderate heat. 
On a large scale, cobalt is extracted from 
its ores only in the state of an oxide, with- 
out being reduced to the metallic form, not 
only as this reduction is difficult, but also 
as the metal is not applied to any use. The 
ore is roasted, by which the sulphur and 
arsenic are expelled, and any fusible metal 
mixed with it is melted out. The cobalt 
remains in the state of an impure o»de, 
Q . W 
if' 
