RAILWAY CONSTRUCTION. ijr 



advocates. In working out the details of any, or all of them, 

 there are some points which should always be kept in mind 

 when deciding the distribution of material in the main booms. 

 Rain-water, or moisture of any kind, is the great enemy of 

 wrought-iron or steel work, and therefore the plates, angles, tees, 

 or channel sections, should be so arranged as to afford the least 

 possible facility for the collection or lodgment of water. With 

 open, level booms, as in Figs. 137, 139, 140, 144, and 145, the 

 rain-water cannot collect, but runs off at the sides, and the plates 

 are quickly dried by the sun and wind. With trough booms, as 

 in Fig. 158, the collected rain-water can only get away through 

 holes drilled for the purpose in the bottom plates. These holes 

 are liable to become choked up, but even when open they rarely 

 carry off all the accumulated water; some of it remains to 

 corrode the plates, and is only dried up by evaporation. The 

 inside of trough booms should be constantly inspected, and the 

 exposed plates more frequently painted than the rest of the girder. 

 In a similar manner, in small double-web lattice girders, with 

 the lattice-bars inserted between two angle irons, as in Fig. 159, 

 the rain-water finds its way into the spaces at A, A, in spite of 

 the most careful packing or filling with cement or asphalte. 

 Numbers of small girders of this latter type have had to be 

 taken out after a comparative short life, in consequence of the 

 great corrosion and wearing away of the lower ends of the 

 lattice-bars and angle irons into which they were inserted. 



It is most essential, also, that all portions of the girder-work 

 should be conveniently accessible for inspection and painting. 

 Complicated connections, and parts which are difficult to examine, 

 are liable to be overlooked, or, at the best, only painted in a 

 very imperfect manner. Neglected corners soon create deterio- 

 ration, the paint scales off, corrosion commences, and the working 

 section is gradually reduced. A discovered weakness in some 

 of the important parts points to an early condemnation of the 

 entire structure. The difficulty of access to the interior of box 

 or tubular girders, especially those of small or moderate dimen- 

 sions, is a great objection to that type of girder. Experience 

 has pointed out that open girders, free and exposed to the light 

 and air, can be so much more effectually inspected and painted. 



Perhaps one of the most anxious tasks which falls to the lot of 

 an engineer is the renewal of under-line bridges and viaducts on 

 a working line. On a new line in course of construction the 



