LOCOMOTIVE ERECTING SHOP, PHILADELPHIA & READING R. R. 375 



splices for the rails being arranged to permit expansion and contrac- 

 tion. The rails were rolled to the recommended Am. So. C. E. sections 

 for their respective weights. The specifications require that the crane 

 track rails must be in perfect alinement horizontally and vertically and 

 that the gage must not vary more than %-in. at the maximum. To 

 obtain vertical alinement it is specified that not more than ^-in. thick- 

 ness of shims, each the full size of the bearings, shall b*. placed between 

 the column top and the girder. The idea, it will be seen, has been to 

 provide for the heavy rolling loads by substantial construction and ac- 

 curate workmanship, and to keep the track smooth and rigid by dis- 

 tributing the expansion over a number of joints instead of having all 

 the allowance made for it at one or two points. 



Turning now to the roof framing, it will be seen from Fig. 177 

 that there is a separate roof over each longitudinal bay of the building. 

 The roof trusses for the middle bay rest directly on the tops of the in- 

 termediate rows of columns, but those for the two side bays are car- 

 ried by special roof columns rising from the main columns, as shown by 

 Fig. 1 80. The trusses in each bay are connected by purlins and lateral 

 bracing and carry lantern roofs with glazing. Details of the roof trusses, 

 bracing and lantern roof construction are shown in Fig. 178 so fully 

 as to make any further description unnecessary. The roof covering and 

 the glazing in the lanterns, however, deserve brief special notice. 



The roof covering consists first of a I x 8-in. hemlock sheathing, 

 having its upper surface planed. This sheathing is to be covered by 

 four thicknesses of roofing felt spread with granulated slag. The con- 

 struction is specified to be as follows: Make the outside course next 

 the edge of five thicknesses of felt, then lay each succeeding layer at 

 least three-fourths of its width over the preceding layer, firmly securing 

 it in place, and thoroughly mop the surface underneath each succeeding 

 layer as far back as the edge of the next lap with a thin coating of roof- 

 ing cement. This cement is in no case to be applied hot enough to in- 

 jure the wooly fibre of the felt. At least 70 Ibs. of felt must be used 

 per 100 sq. ft. of roof. Over the entire surface of the felt laid as de- 

 scribed there is to be spread a good coating of cement, not less than 10 

 gallons (including what is used between the layers of felt) of cement 

 being employed per 100 sq. ft. of roof. This cement coating is to be 

 covered with a coating of slag, granulated and bolted for the purpose, 

 using no slag larger than will pass through a ^-in. mesh and none 

 smaller than will be caught by a %-in. mesh. This slag must be free 



