— ßO — 
When wooden slums arc used, as m Plato ill, tlio tics at the panel points aro 
made of 7" X 14” x 6’ timber so as to span the opening left between tlie ends of tlio 
stringers for tlie passage of tlie lower lateral struts. The ties are dapped about an incli 
onto the shims, whioli are generally of 7 ,f x 8’’ oak， and are connected thereto by drift 
bolts of three quarter inch square iron driven into three quarter inch round holes, 
bored obliquely tlirougli both ties and slums. Tlio bolts are provided witli square 
heads, so that they may bo withdrawn by a claw bar, when tlie timber is to bo 
replaced. The wooden slums are useful in affording an easy means of attaching 
tlie ties to the stringers, besides adding somewhat to tlie strength and stiffness of 
the latter, — enougli in any case to componsato for tlie loss of strength caused by 
the holes for the attaching bolts. Tlie latter should bo staggered and spaced about 
two feet apart, but there should bo no bolt placed nearer than two feet to the middle 
of tlie panel, whore the bending moment on tlie stringer is at a maximum. 
These bolts are to be J" in diameter, and the holes tlirougli wliicli they pass U" iu 
iron find 1" in wood. 
Tlie guard rails are of 5" 乂 4" x 士〃 angle iron, eacli weighing 14^** per lineal 
foot, the five inch log being vertical, and tlie four inch leg perforated for tlio 
passage of tlie 每 " bolts which attach it to alternate ties. 
The distance between the inner face of the head of the rail and the outer face 
of the guard rail is six inches. 
To avoid splitting the wood a small hole should be bored whenever a track 
spike is to be driven. 
When shims aro not used, tlie ties are attached directly to the stringers by bolts. 
By glancing over the bills of iron and lumber in Chapter XVIII and choosing 
those weights which belong to tlie floor system proper, tlie weight of iron per lineal 
foot of span in tills portion of the bridge will bo found to bo 87 pounds and tlio 
weight of lumber per lineal foot 195 pounds. When sliims are not used the weight 
of iron is almost unchanged, but tlio weight of lumber is reduced about 40 pounds 
per lineal foot. 
Plate V illustrates a re-railing device to bo placed at each end of a bridge. By 
its use any car or locomotive which is off the track, at a distance not greater than 
half the gauge ， will bo returned thereto before coming upon tlie bridge. This ingenious 
device is the design of E. McClure, C. E. Esq. use larger letter, Cliie f Engineer of tlie 
Chicago, Burlington and Quincy E. E. system, to w liosc kinduess tlie autlior is indebted 
for tlie drawings from winch Plato Y was prepared. The autlior lias been obliged to 
introduce several unimportant modifications to adapt it; to the change of gauge and 
to the peculiar guard rail employed. 
It consists essentially of an ordinary frog point placed nndway between tlio 
rails at a short distance from tlie end of the bridge, from which point diverge two 
ordinary rails produced until their centre lines approach the centre lines of tlio track 
rails within about a foot. The ends of the former rails rest on an extra wide tic, 
and between each of them and tlio nearest trade rail is a ^ r, plate resting on two 
ties and having the end benfc down. This plafco joins onto a 4：" x G" angle iron 
with the four inch leg vertical, and cut and bent as shown on tlie drawing, tlie outer 
