Washington sentinel. [volume] (City of Washington [D.C.]) 1853-1856, 1855-09-01
From the National Intelligencer
ode OF Testing Building Materials.

Professor Henry read paper Friday, be-
fore the American Association of Science, sitting
at Providence, on the modes Of testing building
materials and account eft the materials used at
Washington He had been appointed on u com
mittee to test the materials offered for the extern
sion of the Capitol at Washington. The commit
tee had to take into consideration many minute
sources of disintegration, such that every flash
Of lightning produced an apprecable amount of
nitric acid, which, diifused IN rain water, acted
on the carbonate Of lime, and the action of dust
carried by the wind against the building. The
committee subjected specimens to actual freezing,
and after several experiments good method was
obtained. 1t was found that in ten thousand years
one inch would be worn from the blocks by the
action of the frost. Blocks of / J inch cube were
subjected to pressure, thin plates of lead as had
been the case in former experiments, being intro
duced to equalize any inequalities which might
| occur in the surfaces But upon experiments il
! was found that while one of these cubes would
sustain GU, 600 pounds without the lead plates, it
would sustain only $1,000 with them They had,
therefore, to invent machine to cut the sides of
the block perfectly PARALLEL when il was found
that the marble which was chosen for the Capitol,
| from quarry in Lee, Massachusetts, would sus-
| tain about 25 600 pounds to the square inch.
The manner of its breaking was peculiar. With
the lead pipes interposed, the sides which were
free first gave way, leaving the pressure on two
cones whose bases joined the plates, and whose
apexes met each other, and they then yielded
with comparative ease.
This marble absorbed by capillary attrac-
ton, and in common with other marble, was per-
meable to gases. Soon after the workmen COM
menced placing it in the walls it exhibited
brownish discoloration, although no trace OF it
appeared while the blocks remained in the stone
cutters yard. A variety Of experiments were
| made with view to ascertain the cause of this
phenomena, and it was finally concluded to be due
to the previous absorption by the marble of water
10
| the absorption of another portion of water from
the mortar. To illustrate the process he sup
posed fine capillary tube, with its lower end inn
| mersed in water, whose internal diameter was suf-
ficenty small to allow liquid to rise to the top to
be exposed to the atmosphere. Evaporation
would take place at the upper surface of the
column, and now portions of water would be
drawn up to supply the loss; and if this process
| were continued any material which nsght be con-
tanned in the water would be found deposited at
the top of the tube, the point of evaporation If,
however, the lower portion of the tube were not
| furnished with supply of water, the evaporation
| at the top would not take place, and the deposit
tioa Of foreign matter would not be exhibited,
even though the tube itself were filled with water
] mpregnated with impurities. The pores of the
marble, so long as the blocks remained in the
I yard, were in this last condition; but when the
same blocks were placed in the wall of the build
| ing the water absorbed from the mortar at the in
terror surface gave the supply of liquid necessary
to carry the coloring materials to the exterior
surface, and deposite it there at the mouths of the
| pores. The cause of the phenomenon being
known, remedy was readily suggested The
/ interior surface of the stone was coated with
| phaltum, rendering it impervious to the moisture
of the mortar, and the discoloration gradual
| ~ disappearing.
| In a series oi experiments made some ten years
ago he had shown that the attraction of the part-
| Giles for each other of substance in liquid form
4 was as great as that Of the same substance in a
solid form. Consequently the distinction between
/ liqudity and sodity did not consist IN a differ
4 ence in the attractive power occasioned directly
by the repusion of heat; but it depended upon the
perfect mobility Of the atoms a lateral cohesion.
/ He might explain this by assuming an incipient
capitalization of atoms into molecules, and con-
slider the first effect of heat as that of breaking
down these crystals and permitting each atom to
move freely around each other. When this crys-
tallne arrangement was perfect, and no lateral
| motion was allowed in the atoms, the body might
| be denominated perfectly rigid We had approx
mately an example of this in cast steel, in which
| no slipping took place of the parts on each
other, or no material elongaton of the mass; and,
| VIXEN rupture produced by tensil force, a
| rod of this material was broken with transverse
fracture of the same size that of the original
| section of the bar. In this case every atom was
| separated at once from the other, and the break
| ing weight might be considered measure of
| the attraction or cohesion of the atoms Of tho
i
when we attempted TO pull apart rod Of lead.
| The atoms of molecules slipped upon each other;
! the rod was increased in length and diminished in
| thickness, until separation produced In
stead of lead we might still softer materials,
| such and putty, until we arrived at a sub
stance in liquid form. This would stand at the
| extremity of the scale, and, between extreme
| rigidty on the one hand and extreme iqudity on
the other, might find series of substances
| gradually sliding from one extremity TO the other
i A al 4 IL
difference in tenacity of steel and lead did not
consist in the attractive cohesion Of the atoms,
but in their capabity of slipping upon each other
From this view il followed that the form Of the
material ought to have some effect upon its tena-
city, and also that the strength Of the article de-
pended in some degree upon the process to which
il had been subjected He had, for instance,
found that softer substances, in which the outer
atoms had freedom of motion, while the inner
ones, by the pressure of those exterior were more
confined, broke unequally; the inner fibres, if he
might so call the rows Of atoms gave way first
and entirely separated, while The exterior fbres
| showed but little indications Of change Of that
kind. fla cylindrical rod Of lead, three-fourths
OF an inch in diameter, were turned down on a
lathe in one part to about half an inch, and then
gradually broken by force exerted in the direc-
ton of its length, it would exhibit cylindrical
hollow along its axis Of half inch in length and
at least tenth of an inch in diameter. With
substances of greater rgdity this effect was less
apparent. 1t existed, however, even in iron;
and the interior fbres of rod Of this metal might
be entirely separated while the outer surface pre-
sented no appearance Of change. From this it
would appear that metals should never be elon-
gated by mere scratching but in all cases by the
process of Withdrawing or rolling. wire or
bar must always be weakened by force which
permanently increases its length without at the
same time COMPRISING il. Another effect Of the
lateral motion of the atoms Of a soft heavy body,
when acted upon by a Dprcussivp force with n
hammer Of small dimensions in comparison with
the mass of metal, was that the interior portion
OF the mass acted as anvil upon which the ex-
terror portion expanded, so TO make il sep
arate from the middle portions. Professor Henry
exhibited portion of bar originally four feet long.
which had been hammered in that way, so as to
produce perforation through the whole length
Of its axis rendering it tube This fact appear
cd to him to be of great importance in practical
point of view, as il might be connected with many