COHESION. 
height of about 60 feet. Dwarf specimens of it, 
in a living state, began to be seen in British hot- 
houses about twenty years before the close of last 
century. 
COHESION. That force which preserves in 
union particles of a similar kind. Its action is 
seen in a solid mass of matter, the parts of which 
cohere with a certain force which resists any 
mechanical action that would tend to separate 
them. In different bodies, it is exerted with 
different degrees of strength, and is measured by 
the force necessary to pull them asunder. Ac- 
cording to Sickengen, the relative cohensive 
strength of the metals is as follows :— 
Gold, . 150,955 
Silver, 190,771 
Platina, 262,361 
Copper, 304,696 
Soft iron, 362,927 
Hard iron, 309,880 
| Cohesion in liquids is very much weaker, the 
| parts being disjoined with much more facility ; 
_ and, in substances existing in the aérial form, it 
is entirely overcome, the particles, instead of at- 
tracting, repelling each other.— Cohesion in 
bodies is weakened or overcome by two general 
causes—by the repulsion communicated by calo- 
ric, or by the attraction which may be exerted 
by the particles of one body on those of another. 
—Caloric communicated to a solid body separates 
its particles to greater distances, as is evident 
from the enlargement of volume which it pro- 
duces. By thus increasing the distances, the 
force with which the attraction of aggregation 
or cohesion is exerted is diminished; if the heat 
be carried to a sufficient extent, the cohesion is 
so far weakened, that the body passes into the 
liquid. form; and, if carried still farther, the 
attractive force is entirely overcome, repulsion is 
established between the particles, and the body 
| passes into the aériform state——The same effects 
are produced by the exertion of that attraction 
which unites the particles of one body with 
those of another. If a liquid be poured on a 
solid, it often happens that their mutual attrac- 
tion is sufficiently powerful to overcome the 
cohesion of the solid: its particles are conse- 
quently disunited, to combine with those of 
the liquid, and it entirely disappears. This forms 
the chemical process of solution, A similar effect 
is sometimes produced by the chemical action of 
an aériform body.—When these powers, whether 
of heat or of chemical attraction, are withdrawn, 
cohesion resumes its force, but with results which 
are different, according to the circumstances un- 
der which this happens.—When the attraction 
of aggregation is suddenly and forcibly exerted, 
the particles are united, in general, indiscrimi- 
nately, and according to no regular law. Ifa hody, 
which has been melted, is suddenly cooled to a 
sufficient extent, it becomes solid,and forms amass 
of no regular structure or figure; or, if its cohe- 
sion has been suspended by the chemical attrac- 
COKE. 859 
tion exerted by another body towards it, and if 
this attraction suddenly cease to operate, the 
force of cohesion is resumed, and the solid sub- 
stance appears in the form of a powder. This lat- 
ter case forms the chemical operation denomi- 
nated precipitation—But, if the force of cohesion 
is exerted more slowly, the particles are united, 
not indiscriminately, but usually with regularity, 
so as to form masses of regular structure and 
figure, bounded by plane surfaces and deter- 
minate angles. This forms the operation of crys- 
tallization ; and such masses are denominated 
crystals. 
COIR. The cordage manufactured from the 
filamentous fibres of the husk of the cocoa-nut. 
It has an astonishing strength and durability ; 
it requires no tar or other application to protect 
it from injury; and it is so elastic that it will 
stretch fifty per cent. of its entire length without 
breaking. It began, a number of years ago, to 
be used for rigging and cables in the British 
navy; and it might very advantageously be used 
for various purposes in the farmery. The manu- 
facture of it, while the Dutch possessed Ceylon, 
was a monopoly, and was supposed to be con- 
ducted to the amount of three millions of pounds 
weight a-year; but both the manufacture and 
the export of it were thrown open by the British. 
COIX. A genus of curious tropical grasses. 
See Jop’s THARS. 
COKE. Most kinds of coal contain sulphur, 
which would be so prejudicial to iron as to pro- 
hibit the use of that material for the purpose of 
smelting the ore. Wood, on the contrary, con- 
tains nothing that can injure iron; but, in its | 
ordinary state, its humidity prevents rapid com- 
bustion, and it will not yield sufficient heat un- 
til it has been converted into charcoal; and then 
it is the very best fuel that can be used, but is 
expensive on account of the labour of preparing 
it, and its very rapid combustion. It is believed 
that Swedish iron—which has for many years 
preserved a higher character for strength, tough- 
ness, and ductility than the metal of any other 
country—owes its perfection to its being manu- 
factured by the charcoal of pine wood; and 
those varieties of iron denominated charcoal tron, 
from a similar process of production, are more 
sought after for good work and command higher 
prices than other iron. Next to the charcoal of 
wood, mineral charcoal, or the cinders of bitu- 
minous coal, called coke, is the best fuel for re- 
ducing iron ore, or melting iron, and this fuel is 
alone used in Britain, where wood is scarce. 
Coke is pit-coal broken into small pieces, ignited 
with free access of air, and permitted to burn 
until it ceases to give out flame or smoke, and 
the whole mass becomes red hot. It is then 
shut up so that the air cannot reach it, when 
further combustion becomes suspended, and in 
this state, after being permitted to cool, it is 
ready for use. The making of coke is carried on 
in a small way, by ovens built for the purpose, 
SSS | 
