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and it necessary a pile driver with its appurtenances. The ordinary weight of a pile 
driver liammoi" varies from sixteen hundred to two thousand pounds, and will pro- 
bably cost from two lmndrod to two hundred aud fifty or even three hundred yen. 
The height of the driver should bo about thirty feet. 
Plate XIi. illustrates nearly all the tools found in the list. The author wishes 
to apologize for the appearance of this plate and its very apparent want of scale ; for 
it was prepared from clippings taken from various advertising circulars. Some of 
the figures clo not represent exactly what they were originally intended for, but the 
agreemeufc is exact cuougli to give the reader a clear idea of the form of each too】. 
Besides the tools on tlie list, each carpenter should be provided with the usual 
special tools to be found in a carpenter's ldfc. 
In getting ready to erect a bridge the first step is to prepare the gi-ound in the 
neighbourhood of tlie site, so that there will be room to store the material and fov 
the men to work. When tlie iron is received at the site it should be checked ； and 
any pieces from which tlie marks have been obliterated should bo remarked. The 
iron should be piled «ystemuticiilly, similar parts being grouped, and no iron should 
be allowed to lio upon tlie gvouiul. It should be piled so that there will be no trouble 
in getting at any piece which may be required. The portions to be used first should 
be placed nearest tlie bridge site. 
Tlie piers aud abutments will be supposed to be erected, as this work does not 
aim to treat of foundations. 
The next step is to put the falsework in place. If the bed of the stream be 
dry or nearly so, tlie bottom hard, tlie distance from the Led to t]io lower chord be 
no greater than twenty feet, aud if there be no danger of a sudden rise of water with 
a swift current, vertical timbers resting on foot blocks with a cap and light diagonal 
bracing may be employed. 
If tlie ground be not perfectly firm, mud sills must be used instead of foot 
blocks, and, H at all soft, piles must be employed. Tlie size of a mucl sill sliould vary 
from 6" x 6” to 12" x 12” according to the hardness of the ground, the weight 
upon the sill and the height of the falsework. It is not necessary that the timbers 
be square : for ground not especially hard wide timbers laid on their flats are pre- 
feriible, as they distribute the press uro bettei*. b^uare timbers should be used where 
tlie ground is haul in some places and soft in others, so as to prevent unequal settle- 
meufc and a consequent distortion of the bent. 
It tlieie be but one tier per bent, two vertical posts will be sufficient for slio 1 *^ 
spans of single track bridges, but in all other cases a third vertical post midway be- 
tween the others will be required. The caps should be from 6” x 8” to 8” x 10" 
according to tlieir unsupported length and the magnitude of the weights which "vvill 
come upon them : they should project two feet beyond each truss. The upper ends 
of tlie posts should lie directly under the trusses, aud the caps slioukl be drift bolted 
thereto. Tlie bent should be braced by diagonal flat timbers, say from 2 n x 6 f, to 
3" x 8"， according to their length, running in opposite directions, one on each side 
of the bent, and bolted or spiked to the posts and cap. • 
