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that though copper can be melted the agent in its case is not water；
but some of the bodies that can be melted by water too such as
natron and salt cannot be softened in water： for nothing is said to be
so affected unless the water soaks into it and makes it softer。）
Some things； on the other hand； such as wool and grain； can be
softened by water though they cannot be melted。 Any body that is to be
softened by water must be of earth and must have its pores larger than
the particles of water； and the pores themselves must be able to
resist the action of water； whereas bodies that can be 'melted' by
water must have pores throughout。
（Why is it that earth is both 'melted' and softened by moisture；
while natron is 'melted' but not softened？ Because natron is
pervaded throughout by pores so that the parts are immediately divided
by the water； but earth has also pores which do not connect and is
therefore differently affected according as the water enters by one or
the other set of pores。）
Some bodies can be bent or straightened； like the reed or the withy；
some cannot； like pottery and stone。 Those bodies are apt to be bent
and straightened which can change from being curved to being
straight and from being straight to being curved； and bending and
straightening consist in the change or motion to the straight or to
a curve； for a thing is said to be in process of being bent whether it
is being made to assume a convex or a concave shape。 So bending is
defined as motion to the convex or the concave without a change of
length。 For if we added 'or to the straight'； we should have a thing
bent and straight at once； and it is impossible for that which is
straight to be bent。 And if all bending is a bending back or a bending
down； the former being a change to the convex； the latter to the
concave； a motion that leads to the straight cannot be called bending；
but bending and straightening are two different things。 These； then；
are the things that can； and those that cannot be bent； and be
straightened。
Some things can be both broken and comminuted； others admit only one
or the other。 Wood； for instance； can be broken but not comminuted；
ice and stone can be comminuted but not broken； while pottery may
either be comminuted or broken。 The distinction is this： breaking is a
division and separation into large parts； comminution into parts of
any size； but there must be more of them than two。 Now those solids
that have many pores not communicating with one another are
comminuible （for the limit to their subdivision is set by the
pores）； but those whose pores stretch continuously for a long way
are breakable； while those which have pores of both kinds are both
comminuible and breakable。
Some things； e。g。 copper and wax； are impressible； others； e。g。
pottery and water； are not。 The process of being impressed is the
sinking of a part of the surface of a thing in response to pressure or
a blow； in general to contact。 Such bodies are either soft； like
wax； where part of the surface is depressed while the rest remains； or
hard； like copper。 Non…impressible bodies are either hard； like
pottery （its surface does not give way and sink in）； or liquid； like
water （for though water does give way it is not in a part of it； for
there is a reciprocal change of place of all its parts）。 Those
impressibles that retain the shape impressed on them and are easily
moulded by the hand are called 'plastic'； those that are not easily
moulded； such as stone or wood； or are easily moulded but do not
retain the shape impressed； like wool or a sponge； are not plastic。
The last group are said to be 'squeezable'。 Things are 'squeezable'
when they can contract into themselves under pressure； their surface
sinking in without being broken and without the parts interchanging
position as happens in the case of water。 （We speak of pressure when
there is movement and the motor remains in contact with the thing
moved； of impact when the movement is due to the local movement of the
motor。） Those bodies are subject to squeezing which have empty
pores…empty； that is； of the stuff of which the body itself
consists…and that can sink upon the void spaces within them； or rather
upon their pores。 For sometimes the pores upon which a body sinks in
are not empty （a wet sponge； for instance； has its pores full）。 But
the pores； if full； must be full of something softer than the body
itself which is to contract。 Examples of things squeezable are the
sponge； wax； flesh。 Those things are not squeezable which cannot be
made to contract upon their own pores by pressure； either because they
have no pores or because their pores are full of something too hard。
Thus iron； stone； water and all liquids are incapable of being
squeezed。
Things are tractile when their surface can be made to elongate；
for being drawn out is a movement of the surface； remaining
unbroken； in the direction of the mover。 Some things are tractile；
e。g。 hair； thongs； sinew； dough； birdlime； and some are not； e。g。
water； stone。 Some things are both tractile and squeezable； e。g。 wool；
in other cases the two qualities do not coincide； phlegm； for
instance； is tractile but not squeezable； and a sponge squeezable
but not tractile。
Some things are malleable； like copper。 Some are not； like stone and
wood。 Things are malleable when their surface can be made to move （but
only in part） both downwards and sideways with one and the same
blow： when this is not possible a body is not malleable。 All malleable
bodies are impressible； but not all impressible bodies are
malleable； e。g。 wood； though on the whole the two go together。 Of
squeezable things some are malleable and some not： wax and mud are
malleable； wool is not。 Some things are fissile； e。g。 wood； some are
not； e。g。 potter's clay。 A thing is fissile when it is apt to divide
in advance of the instrument dividing it； for a body is said to
split when it divides to a further point than that to which the
dividing instrument divides it and the act of division advances： which
is not the case with cutting。 Those bodies which cannot behave like
this are non…fissile。 Nothing soft is fissile （by soft I mean
absolutely soft and not relatively： for iron itself may be
relatively soft）； nor are all hard things fissile； but only such as
are neither liquid nor impressible nor comminuible。 Such are the
bodies that have the pores along which they cohere lengthwise and
not crosswise。
Those hard or soft solids are apt to be cut which do not necessarily
either split in advance of the instrument or break into minute
fragments when they are being divided。 Those that necessarily do so
and liquids cannot be cut。 Some things can be both split and cut； like
wood； though generally it is