Concrete may be defined as a sort of liquid masonry which, poured from a height into a mould prepared for its reception, hardens into a mass of solid stone. The materials generally used in its composition are gravel and broken stone mixed thoroughly with lime while water is thrown upon the mass, which while still warm is poured from elevated stages into the trenches dug to receive it. When work is done very hastily, as the lime may not be thoroughly slaked and the process may continue with injurious effects, it is recommended that the concrete, immediately after mixing, be gently tipped from wheelbarrows into the trench prepared, and rammed down in layers about a foot in depth. W'hen broken stone or masons' chips are used for the compound, sharp sand is added. As a general rule, the pieces of stone should never be larger than a hen's egg. Thorough and careful mixing of the components greatly increases the value. Hydraulic• lime and the addition of volcanic sand improve its quality, and an excel lent composition is formed by the mixture of Portland cement with sand and gravel.
Timber and Lumber.—Woodin various forms and of sundry kinds con tinues to be used extensively in the interior arrangements of nearly all American buildings, and to furnish the exterior material of a large 1111111 ber of the dwellings located in rural districts, villages, and towns. The articles quoted in price-lists of builders' materials include different qualities of pine, pine boards, pine plank, spruce boards, spruce plank, spruce wall strips, spruce timber, hemlock boards, hemlock joist, ash, oak, maple, chestnut, cypress, black walnut, cherry, whitewood, yellow dressed pine flooring, yellow pine girders, locust posts, and chestnut posts. Estimates of the cost of designs for cottages frequently embrace a liberal allowance for timber bills and for other wooden materials, including those used in flooring,r, verandas, balconies, windows, doors, and stairs. A large propor tion of the dwellings erected by the early settlers of nearly all localities in the United States was composed chiefly of wood, and this custom continues to prevail to a considerable extent, the ordinary course of progression ,be ing from log cabins, frame or weatherboarded houses, to stone or brick dwellings.
Strength and Durability of Timber.—lt is said that there are certain indications characteristic of strong and durable timber, which include the following: (r) In the same species of timber that log will, in general, be the strongest and the most durable which has grown the slowest, as shown by the narrowness of the annual rings; (2) The cellular tissue should be hard and compact; (3) If the wood is colored, darkness of color is gen erally a sign of strength and durability; (4) The freshly-cut surface of the wood should be firm and shining instead of dull and chalky; (5) In wood of a given species the heaviest specimens are generally the strongest and most durable; (6) Among resinous woods those which have least resin, and among non-resinous woods those which have least sap or gum, in their pores are generally the best. Superior qualities of timber are free from such blemishes as clefts or cracks radiating from the centre, cracks which partially separate one annual layer from another, wounds in a layer of the wood which have been covered or concealed by the growth of subsequent layers over them, and hollows or spongy pieces in the centre and else where, indicating the commencement of decay.
Grades of Lumber.—The nature of recognized defects in hard-wood lumber is shown by provisions in the Boston law for the survey of black walnut and cherry, oak, poplar, and butternut, which reqnire that the woods be divided into three grades—namely, number one, number two, and culls. Number one includes all boards, plank, or joist that are free from rot and shakes and nearly free from knots, sap, and bad taper; the knots must be small and so far sound that they would not cause waste for the best kind of work. A board or plank with a split parallel with the edge of the piece is classed as number one. Nmnber two includes all other descriptions, except when one-third is worthless. When a board, plank, or joist contains sap knots, splits, or any other imperfections combined, making less than one-third of a piece unfit for good work and fit only for ordinary purposes, it is number two. When one-third is worthless, it is a cull, or refuse. Refuse or cull hard wood includes all boards, plank, or joist that are manufactured badly by being sawed in diamond shape smaller in one part than in another, split at both ends or with splits not parallel, large and bad knots, worm-holes, sap, rot, shakes, or any imperfections which would cause a piece of lumber to be one-third worthless or waste. All hard woods are measured from 6 inches up, and all lumber sawed thin is inspected as if it were of proper thickness, but is classed as thin and sold at the price of thin lumber.
Iron.—The use of iron in the construction of large and important build ings, and various classes of shops, mills, stores, and factories, is increasing. The purposes to which it is applied include the support of walls, floors, and roofs. In addition to a growing demand for standard qualities and shapes, iron, either corrugated or galvanized, is being used to an increas ing extent for roofing, and in some cases for exterior surfacing. The avail able appliances include cast-iron columns; hollow cylindrical or rectangu lar cast-iron pillars; cylindrical cast-iron columns; wrought-iron posts and. columns, I-beams, channels, T-bars, angle-irons, and deck-beams used as posts; rolled beams and channels used as struts; angle and T-bars used as struts; wrought-iron rivetless columns; riveted plate-iron girders; cast iron arch girders with wrought-iron tension rods; and stirrnp-irons. Am ple provision is made for variations in the weight and strength of each of the standard articles, and ingenious devices for combining- component parts have been perfected. Great progress has been made in the United States, during a comparatively recent period, in many things pertaining to the use of iron in construction. Galvanized iron is sheet iron covered on both sides with a thin film of zinc, which is applied mainly because zinc resists corrosion from ordinary atmospheric influences much better than iron. Corrugated iron, which may or may not be g-alvanized, is sheet iron in corrugated forms. Advocates of the use of corrugated iron—which, as a covering for buildings, is now made in improved forms—allege that it is fire-, water-, and wind-proof to a high degree; that the corrugations lend the iron considerable additional stiffness, on which account, the strength acting as a support, framework may be comparatively light; mild that cor rugated sheeting is cheap and durable if properly painted.