— 176 — 
The track rails with their fish plates and attaching spikes do not belong to the 
bridge, for they would have to be provided if the bridge did not exist, bo their 
weight is not included in tho ** Bill of Iron”， bufc must be afterwards allowed for 
in checking the dead load : it may be taken to be 45 pounds per lineal foot. Lock 
nuts will be used on counters, lateral rods, vibration rods and beam hangers : let us 
average their weight at eacli. An allowance of 50 pounds will be sufficient for 
pilot nuts. 
The total weight of rivet heads may be calculated from the group in the list 
of members, but it is not* worth while to do so ; for, if three per cent, be added to tlie 
total weight of iron, it will cover tlie weight not only of the rivet heads, but also that 
of the allowance for rivets lost during erection. 
The 14 Bill of Lumber” needs no explanation, except that there is an allowance 
for an extra tie at each end of the span. 
