Gloucester County Democrat., 1911-11-09
A ROPE OF WATER.
BertheIot's Test That Showed Its
Tensile Strength.
THE COHESION OF MATTER.

Perfect Planes Of Metal or Glass When
Brought Into Contact viii Adhere to
One Another as Though They Were
Glued Together.
1t is well known that liquids are
among the least compressible Of sub
stances; this in spite of the fact that
they have the property of conforming
to any shape Of vessel or of yielding
to any forces. no matter how small,
which tend to change only their shape.
Thus. to squeeze water into nine
tenths of its volume under ordinary
conditions would require pressure
of no less than 5000 atmospheres, or
5000 pounds. to the square inch.
This property of being almost incom-
pressible is best illustrated perhaps
by an experiment tried centuries ago,
wherein an attempt was made to COM
press water by filling leaden shell
with it and then, after closing. ham,
mering and squeezing the she'll The
only effect of the tremendous pres
sures produced In this way was to
cause the water to penetrate the mi
mute pores Of the lead and exude in
drops like perspiration on the outer
surface of the shell. The same effect
was found for silver she'll.
But, while it is a familiar fact that
liquids will resist an enormous force Of
compression. the companion fact that
they are also capable of withstanding
tension is not so generally known. At
first sight this statement may appear
/ ridiculous. When water may be so
readily dipped from pail or poured
| from one vessel to another, how can
1t be capable of withstanding tension?
J If. however, we prevent change OF
form we find that pure water is capa-
Bile of bearing fifty atmospheres of ten
sion. or 750 pounds to the square inch
If it was possible. then. to utilize this
property by making rope" of water
we should find it capable of sustaining
good fraction of the weight that
could be borne by an ordinary rope OF
| the same size. But it must be admit
ted that the task of making rope out
of such material would be rather diff
ficult, to say the least. Notwithstanding
the fact that 1t possesses this desirable
property of tensile strength. Because
of its inability to resist deforming
force it would have to be inclosed in
tube; but, while 1t would here be In
condition to withstand compression. as
from a piston In the tube, any attempt
at stretching the liquid in this way
would simply result in pulling away
the piston from the water surface.
/ However, this tensile strength was
actually found by Berthelot in the fol
lowing way: A strong glass tube sealed
at one end and drawn out very fine at
the other was filed nearly full of wa
i ter and then closed The tube was then
cautiously heated until the water had
expanded and completely filed it. 1t
was then slowly and carefully cooled
back to its original temperature. when
it was found that the water had not
contracted. but still filed the tube.
| 1t is almost a universal law that
| small extension in volume of a body
requires the same magnitude of force
| to produce 1t as to cause similar
amount of compression. the forces. how
ever, being tension in one case and
compression in the other. With this
law in mind it is readily seen that the
water that now fills the tube must be
under tension. since previously at the
same temperature it did not quite fill
the tube-that is, it has actually been
stretched or expanded beyond its nor
NAL volume for this temperature and
from our knowledge of the forces that
would be required to produce the corr
responding compression we can figure
out what this tension must be-
The ultimate particles or molecules
of matter we believe to be held to-
gether by powerful forces. known va
riously as cohesion or adhesion, but
being in any case forces of attraction.
and these forces tend to prevent any
expansion of the matter. be it solid or
liquid 1t might be thought that these.
forces would cause two bodies in con-
tact to adhere to each other. but par
ticles have to be so near together to
be acted upon by them that it is diff
ficult to bring bodies into such close
contact that an appreciable area of
one is within this distance of the other.
However. two clean pieces of lead
can readily be pressed so closely to-
gether that they will adhere. and a
set of copper cubes was once made
with such true faces that when a doz-
en- of them were piled one on top of
the other the series adhered together
so well that the whole could be lifted
from the top one But the best ex-
ample is furnished by pieces Of op-
tical glass whose surfaces have been
worked SO plane that when pressed to-
gether they will as readily break at
some other spot as at this plane
Perhaps it is unfortunate that these
f,,1 h1lI Ill