Promoter's inflated ideas. — Keeping down first cost. — Traffic investigation. —

Revenue investigation. — Maintenance and repairs. — Determination re under-taking the proposed venture. — Pedestrian traffic. — Initial temporary economic expedients. — Constructions part permanent part temporary. — East Omaha Bridge. — Growing scarcity of timber .................................... 20

Comparative unimportance of market price variations. — Structural metal price

variations. — Cement price variations. — Monograph on "Economic Span-lengths for Simple-truss Bridges on Various Types of Foundation." — Suspension-bridge price-variations. — Location affecting economic layout ............. 23

Three fundamental conditions affecting economic question. — Economic criterion

for rods or bars. — Economic criterion for plate-girder spans. — Economic criterion for long spans. — Examples computed. — How economic curves were established. — Extension of economic curves into "speculative zone." — Cutting out carbon steel entirely in very-long-span bridges. — Accuracy of the curves. — General applicability of curves for all cases. — Use of alloy steel for bridgework in its infancy. — Author's investigation on "Nickel Steel for Bridges." — Present great demand for nickel prohibits use in bridges. — Other alloys of steel for bridgework. — High-carbon steel not advisable for bridges. — Mayarí Steel. — Vanadium steel. — Silicon steel. — "Purified steel." — Aluminum steel. — Molybdenum steel. — Nichromol steel. — Improvement by French scientists on Bessemer process. — Study on economics of molybdenum steel for bridgework. — Catalogue re "Molybdenum Commercial Steels." — Proposed nomenclature for various molybdenum-steel alloys. — Legitimate working intensities for molybdenum steel alloys. — Meagreness of data. — Heat-treated chrome steel with and without molybdenum. — Heat-treated chrome-nickel steel with and without molybdenum. — Heat-treated chrome-vanadium steel with and without molybdenum. — Heat-treated nickel steel with and without molybdenum. — Heat-treated carbon steel with molybdenum. — Untreated and treated chrome steel with molybdenum. — Assumed unit prices erected for alloy steels. — Best drawing temperature for alloy steels in bridgework. — Carmol steel versus carbon steel. — Chromol steel versus chrome steel. Nicmol steel versus nickel steel. — Nichromol steel versus nichro steel. — Chrovanmol steel versus chrovan steel. Best percentage of molybdenum for alloy steels in bridgework. — Compilation of results. — Most promising molybdenum alloy for bridge steel ....................................... 26