The Cairo bulletin., 1911-07-23
A ROPE OF WATER.
BertheIot's Test That Showed Its
Tensile Strength.
THE COHESION or MATTER

Perfect Planes of Metal or Glass When |
Brought Into Contact Will Adhere TO
One Another as Though They Were
Glued Together.
Ii is well known that liquids arc
among the least rompressit'e Of sHD
stances: this Ia spite OF the fact that
they hare The property of conforming
to any shnpe Of vessel or Of yielding
to any forces. 40 mnttpf how small,
Witch tend 10 change onlr their shape.
THUS, to sn1ec2e water into nine
tenths Of It's volume under ordinary
conditions woald require pressure
of no less than ..GOO atmosphereS, or
5000 pounds. TO the square inch,
This property Of being almost incon
pressiIle Is best illustrated perAllS
by an experiment tried centuries ago,
wherein IN attempt was made 10 com
press water bY tiling 4 l"ndei shell
with It ard then. after closing. ham
mering aud squeezing the she'll The
only effMl Of the tremendous pres
sures produced IN this WAY was 70
cause the water to penetrate the mi
mite pores Of the lead aud exude in
drops like perspiratlon on the outer
surface Of the shell The same effect
was fouud FOR 4 silver shell.
But. while It is II familiar fnct that
liquids Will resist On enormous force of
compression. the companion fact that
they are also capable of wiihStand'ng
tension is not so generally known At
first sight this statement may appear
ridiculous. Wheu, water may be so
readily dipped from a pail or poured
from one vessel TO another. how can
1t he CAPABLE of wthstandiug tension:
IL, however we prevent change Of
form wp find that pure water II capa-
Bile of hearing City atmosphercS OF ten
sion. or 40 pounds to The square inch,
If it was possible, then, to utilize this
property 10y making 4 ''rope" Of water
we should GCJ It capable of sustaining
a good fraction Of the weight that
could lie bone by an ordinary rope OF
the same size. But II must he admit
ted that The task of making a rope out
Of such material would be rather diff
hcul. to say tbellcast. Notwithstanding
the fact that ii possesses this desirable
property c. tensile strength. Because
Of It's inability to resist deformiuG
force ii would have TO he mcInsed in Il
tube: but. while it would here he in
condition 10 withstand compression. IS
from Il 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 WIS
actually found by Bertheot in the fol.
lowing way: \ strong glass tube sealed
at one end aud drawn out very tne at
the other was flied nearly full Of WV
| ter aud then closed The tube was then
cautiously. heated until the water had
expanded and completely filled It, 1t
was then slowly and carefully cooled
back to IFS original temperature, when
it was found that the water had not
contracted, but still filed the tube.
1t is almost a universal law that n
small extension in volume Of a body
requires the same magnitude of force
to produce it as TO cause simiIar
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 moi quite FIJI
| the bethat is, il 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 cor.
responding compression we eau figure
ont what this tension must be-
! The ultimate particles or molecules
Of matter we believe to he held TO-
gethcr by powerful forces, known va
riousy MS cohesion or adhesion, but
| being in any case forces OF attraction.
aud these forces tend to prevent any
expansion OF the matter, he 1t solid or
| liquid II might he thought that these
| forces would cnlse two bodies in con,
| tact TO adhere to each other hut par
| ticles have to be SO near together to
! be acted upon by Them that it Is diff.
| hcult 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 q
set of copper cubes was once made
| with such true faces that when do2
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 ox'
| ample Is furnished by pieces Of op'
| tIca glass whose surfaces have been
| worked so plane that when pressed to-
gether they will as readily break al
some other spot as at this plane.
Perhaps 1t is unfortunate that these
| useful forces. which hold all matter
together and keep il from cnlIapsine
into impalpabe dust, are confined IN
their action to such limited range
II this were not so. q break of any
sort could he fixed by merely bring
ing together the broken ends Glue
of any kind would he unnecessary.
H.. III