BRITTLENESS, that quality of bodies on ac-
count of which they are denominated brittle, or which
subjects them to be easily broken by pressure or per-
cussion.
Brittle bodies are extremely hard; a very small per-
cussion exerts a force on them equivalent to the great-
est pressure, and thus may easily break them. This
effect is particularly remarkable in glass suddenly cooled,
the brittleness of which is thereby much increased.
Tin, though in itself tough, gives a brittleness to all
the other metals when mixed therewith. The brittle-
ness of glass has been said to arise from the heteroge-
neity of the parts whereof it is composed, as salt and
sand can never bind sufficiently together; but this can-
not be the case; for the pure calces of metals, or any
other simple substances when vitrified, become brittle
also. In timbers, brittleness seems to be connected
with durability; the more brittle any sort of wood is,
the more durable it is found. Thus oak is of very
long duration; while beech and birch, as being tough,
presently rot, and are of little service in building.