The San Francisco call. [volume] (San Francisco [Calif.]) 1895-1913, 1896-12-26
STRENGTH TEsTING MACHINES.
Peril In The Tests When Applied to
Blocks of Stone

ferll In ine rests when Applied to
Blocks of Stone.
One of the most interesting places in the
city of Boston to one of a mechanical turn
of mind is the engineering building of the
Massachusetts, Institute of Technology,
and especially that part of it where tests
of strength OF different materials are
made. The testing plant is one of the
best in the country, and the test of the
strength of about anything, from Irvine to
iron columns, can be made. 1t is not gen.
orally known, but it is fact, that it was
at this plaat that the first test of large
beams. columns, etc., for buildings were
made, and as q result of the discoveries
which were made by these tests the build
ing laws all over the world were changed.
The most interesting discoveries were
made with regard to the strength OF
wooden beams. Previous to this test the
strength OF beams had been figured by
testing small pieces of the same kind of
wood and then calculating the strength OF
the beam from the strength shown by
these small sections. In making these
calculations the small pieces which were
tested were taken perfectly, clear ard free
of knots, and allowance was made for the
weakening of the beams by the imperfec-
tions in them. AS result of the tests
made at the institution on entire beams ii
was shown that this allowance was not
nearly large enough and that for some
time beams had been figured on to carry
loads which would bring them danger
ously near their breaking point.
The most imposing figure in the testing
plant at present is the big machine which
is used for crushing and tensile tests. The
machine is an Emery patent and is on
49, v1.,,@ L. - -
Watertown Arsenal, although 1t is not so
powerful, the latter being the biggest in
the world. The institutes machine has a
strength of only 300, 900 pounds, but this is
enough for any tests which are made
there, and, in fact, for the large majority
of the tests which are made at the arsenal.
This machine will crush a great iron
column together endwlse in its powerfuT
grasp or will pull it apart as confectioner
pulls molasses candy.
More spectacular than such tests as these
are those made on wooden beams, when
the great tim bers, after resisting to their
utmost, bend upward and then break with
a tremendous, rending crash. The most
dangerous tests are those made on blocks
of stone, granite especially. A block of
granite will resist almost to its breaking
point without giving any sign, and when
1t goes it goes with report like a small
cannon, and is reduced almost to powder.
The small fragments fly with tremendous
velocity, and it is necessary in making q
test of this kind to cover the objects with
thick layers of cloth to prevent the wound
ing of the students.
Over in the corner of the basement is
the torsion machine, one of the most in
teresting in the whole plant. 1t is pow
erful enough to twist three-inch bar OF
the finest wrought steel an unlimited
number of times. 1t is surprising the
extent to which a bar of good material
will twist before breaking. There are at
the institute some bars of Norway iron
which have been twisted round and round
twenty times in a length of six feet, and
the pitch is as even as though it had been
cut with a machine. Domestic iron, on
the contrary, will stand hardly any twist
without breaking. The means by which
the twist is measured is remarkably inter-
esting. Two telescopes are mounted on
the par before the twisting process is be-
gun, and these are sighted on graduated
scale on the wall across on the other sid 9
of the shop, and by this means the
slightest movement of the bar can be read
with the greatest distinctness. ft seems
almost incredible, but 1t is possible for 8
| man to take hold of the bar when it has
been clamped into the machine, and by
twisting it with one hand to produce "A
movement which is discernible on TIE
scale on the wall.-Boston Evening Tran.
sCrIDt