New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1871-07-18
TINE TOVCVSTOHE.

The ChicGgo Railroad Gazette states That the
Canadian Inter-ColOnial Railway, which is to
connect Halifax directly with Quebec, publicly
solicited, some two or three months since,
proposals for supplying the Bridges needed on
their line, under specifications rigidy requlr-
ing each bridge to be constructed wholly of
wrought non, and capable of sustaining, IN
addition to their own weight, pressure OF 1t
TIM per lincal foot without straining the iron
in tension TO over 10000 pounds per square
inch. The iron of the 20O-fcct spans was to be
capable of bearing 10000 pounds per square
inch before breaking; chat of the 100fcet spans,
$4,000 pounds per square inch.
The competition for this work was extensive
and eager-10 British, IS American, and
Belgian concern having submitted tenders or
bids-eacb, of course, in ignorance of every
other. After a careful scrutiny, the short
spans were awarded to the Fairburn Manufac-
turing Company, Manchester, England, and
the long spans to Clark, Reeves g. Coz Phoenix
vile, Penn, who were the lowest bidders.
They work with dearer labor and use dearer
from but they know how TO achieve the
requisite strength with less weight or quantity
of material, and thus construct a cheaper as
well as better bridge. Says The Railroad
| Gazette:
"some persons erronoousy suppose that the more iron
there in bridge the stronger it viii he. But little
reflection will show that It is only iron that is work
ing or in other Words that is actually strained by the
load that contributes TO the strength OF tho structure
All the rest is dead weight, and merely weighs down the
bridge in very short spans this is not dsadyantage0us,
as It tends to diminish vibrations but in long spans
where the weight OF the bridge much exceeds that of the
l,adp % hat dOpa ut
contribute to tho strength of the bridge ia positive in
Jury. 10 illustrate TINS more clcarly-if bridge
weighs 25 tuns and another go. aud both
by the rolling load 10000 lbs per square inch the lighter
is the stronger Of the two. But If the 125un bridge be
strained 10000 lbs per square inch, while the 25otun
bridge strained only 5000 lbs per square nch then the
latter has really double the strength and double the life
Of the former for half the iron may cOrrode away, and
then the working of tho bar will be equal 1t is not
clearly perccivng this fac-that the strength Of the
bridge depends upon the working area OF its partsthat
has led our English friends to make such heavy bridges
"In several plans If the strain square inch is alike
for similar loads they must all be OF the strength
| providing the connections equally perfect. Some
take iron than others to effect the result but the
! result Is the same
The ghtness American bridges IS due. LIST, to the
concentration Of material along the lines of strain
which enabled lighter web system to be used, and
hence higher truss 3D. to this greater hight of truss
which throws less leverage tho upper and lower
chord system and henc requires less iron in their
bers 3D. TO the OF eye and pin connections instead
OF ryets, by which there Is waste OF metal to
pensate for the deduction Of riyehOles
american bridges are sitter vertically, and better
bfaced laterdly. than English bridges their greater
hight giving less detection under load and allowing OF
overhead bracing, as well IA that below the track.
But the less quantity of iron required to do the
ia the whole explanation of the less cost OF Amer
can as compared with English bridges. second and
equally important reason Is the less amount OF manual
labor required TO construct and erect themOwng the
general Of machinery formingal the parts. En-
gsh bridges are made OF lowprced iron and require
great deal of it, and great deal Of hand labor In con-
stTucting and erecting.
american bridges have all their principal parts formed
by machinery. They exact, uniform dimensions,
I'm similar spans and hence perfectly interchangeable
like the parts OF tho locks of the American rifles OF
sewing machines Hence. machinelabor can be applied
10 their manufacture, aud the cost at the works reduced
! TO minimum.
| "But American bridges have st another advantage
They 30 made that nearly all the work Is done at the
shops, and they be erected with the least possible
erecting the staging is the principal expense; after that
2Ooieet span can be erected and made sefsustaning
| In the space OF two DAYS. II necessary.
But the English bridge IA only about half done when
the scaGodng Is built and the iron placed upon It, IL
has then TO he ryeted together, which s expensive
the cOuvenonces Tor such work at the site OF bridge
not often great II Ia slow and tedious. reeliIIg