Mr. Heritage's contribution to this chapter. — Definition of most economical

structure. — Periodical inspection. — Inspection departments. — Repairs to timber bridges and pile-driven trestles. — Tools for bridge-repairing gangs. — Preservation of timber. — Fire protection. — Planks no longer fit for highway bridge-floors. — Old masonry piers and abutments. — Repointing. — Concrete piers. — Steel cylinder piers. — Protection against corrosion of steel. — Paint and painting. — Cleaning of metalwork. — Application of paint. — Spraying of paint. — Signs of deterioration in connections. — Wear on pins. — Wear at intersection of diagonals. — Overstress on counters. — Joint contribution of Mr. Chalfant and Mr. Covell. — Division of subject. — Masonry. — Scouring of bed and cutting of banks. — Turning of stream. — Rip-rapping. — Systematic soundings. — Floors. — Best type of pavement and base. — Concrete slab. — Buckle-plate floors. — Plank floors are antiquated. — Weight of trucks too great for timber floors. — Nailing-pieces for stringers. — Stringer-spacing. — Laying of planks. — Rail supporting. — Laying of wood-blocks. — Hillside blocks. — Crowning of roadway. — Sidewalks. — Adjusting old back-wall to new grade. — Replacing of floors. — Itemized record of repairs. — Detection of decay in timber. — Painting. — Division of territory for painting. — Colors for bridge paints. — Cleaning and repainting of metal below flooring. — Paint formula. ...................... 407

Importance of proper protection of metalwork. — Duration of life of metallic

structures. — Subjects included in the economics of metal protection. — Best kinds of paint for shop and field. — Author's experience with paints. — Ideal paint for shop coat. — Finishing coats. — Havre de Grace test of paints. — Houston Lowe's conclusions concerning the characteristics of good bridge paints. — Objections to the old-fashioned, red-lead paints. — Amount of red-lead pigment per gallon of vehicle. — Varying elasticity of paint coats. — Functions of an anti-corrosive metal-coating. — Best vehicle for paint. — Author's experiments on paints in Mexico. — Use of driers. — Best colors for paints. — Covering and spreading powers of paints. — Cement paints. — Linseed oil alone for shop coat. — Climatic influences on paints. — Salt-water-proof paint. — A special paint for the hot climate of Brazil. — Spraying of paint. — Spraying on metalwork for shop coat. — Cleansing paint. — Pickling. — Painting newly-erected steelwork. — Concrete encasement. — Gunite. Treatment of steel that has to be encased in concrete or gunite. — Protection against brine drippings. — Protection against locomotive gases. — Causes of paint deterioration. — How to care for incipient failure of paint. — Determination of time for repainting. — Cleansing of metalwork preparatory to applying new field coats. — Application of paint after cleaning. — Factors that affect results in painting. — Economic observations concerning painting in general. — Price of paint. — Thickness of coats. — Character of brush. — Best temperature for painting. — Special kinds of paint for special conditions. — Summary. ............... 430

Aid from Mr. J. B. W. Gardiner. — Definition of economics of water-proofing. —

Profitableness of water-proofing. — Factors affecting cost of water-proofing. —