VIII. WOOD. TIMBER, KINDS OF (Art. 212). Parts and properties of the trunks of Trees (Arts. 213-214). Felling of Trees (Arts. 215-216). Girdling and barking trunks of Trees (Art. 217). Methods of seasoning Timber (Arts. 224-225). Wet and dry rot (Art. 226). Preservation of Timber (Arts. 227-242). Forest Trees of the United States (Arts. 243-248). IX. METALS. CAST IRON, VARIETIES OF (Arts. 249-263). Wrought Iron, Varieties of (Arts. 264-277). Durability of Iron (Arts. 278-289). Preservatives of Iron (Arts. 290-298). Corrugated Iron (Art. 299). Steel (Art. 300). COPPER and its alloys (Art 301). ZINC and its alloys (Art. 302). TIN (Art. 303). LEAD (Art. 304). X. PAINTS AND VARNISHES. Varnish for Zincked PAINTS, COMPOSITION, USES AND DURABILITY OF (Arts. 305-308). Varnishes, Composition and Uses of (Arts. 309-311). Iron (Arts. 312-313). Zoofagous Paint (Art 314). ing exposed surfaces of Stone (Art. 315). 1. A KNOWLEDGE of the properties of building materials is one of the most important branches of Civil Engineering. An engineer, to be enabled to make a judicious selection of materials, and to apply them so that the ends of sound economy and skilful workmanship shall be equally subserved, must know: 1st. Their ordinary durability under the various circumstances in which they are employed, and the means of increasing it when desirable. 2d. Their capacity to sustain, without injury to their physical qualities, permanent strains, whether exerted to crush them, tear them asunder, or to break them transversely. 3d. Their resistance to rupture and wear, from percussion and attrition. 4th. Finally, the time and expense necessary to convert them to the uses for which they may be required. 2. The materials in general use for civil constructions may be arranged under the three following heads :— 1st. Those which constitute the more solid components of structures, as Stone, Brick, Wood, and the Metals. 2d. The cements in general, as Mortar, Mastics, Glue, etc., which are used to unite the more solid parts. 3d. The various mixtures and chemical preparations, as solutions of Salts, Paints, Bituminous Substances, etc., employed to coat the more solid parts, and protect them from the chemical and mechanical action of atmospheric changes, and other causes of destructibility. I. STONE. 3. The term Stone, or Rock, is applied to any aggregation of several mineral substances. Stones, for the convenience of description, may be arranged under three general heads-the silicious, the argillaceous, and the calcareous. 4. SILICIOUS STONES. The stones arranged under this head receive their appellation from silex, the principal constituent of the minerals which compose them. They are also frequently designated, either according to the mineral found most abundantly in them, or from the appearance of the stone, as feldspathic, quartzose, arenaceous, etc. 5. The silicious stones generally do not effervesce with acids, and emit sparks when struck with a steel. They possess, in a high degree, the properties of strength, hardness, and durability; and, although presenting great diversity in the degree of these properties, as well as in their structure, they furnish an extensive variety of the best stone for the various purposes of the engineer and architect. 6. Sienite, Porphyry, and Green-stone, from the abun dance of feldspar which they contain, are often designated as feldspathic rocks. For durability, strength, and hardness, they may be placed in the first rank of silicious. stones. 7. Sienite consists of a granular aggregation of feldspar, hornblende, and quartz. It furnishes one of the most valuable building stones, particularly for structures which require great strength, or are exposed to any very active causes of destructibility, as sea walls, lighthouses, and fortifications. Sienite occurs in extensive beds, and may be obtained, from the localities where it is quarried, in blocks of any requisite size. It does not yield easily to the chisel, owing to its great hardness, and when coarse-grained it cannot be wrought to a smooth surface. Like all stones in which feldspar is found, the durability of sienite depends essentially upon the composition of this mineral, which, owing to the potash it contains, sometimes decomposes very rapidly when exposed to the weather. The durability of feldspathic rocks, however, is very variable, even where their composition is the same; no pains should therefore be spared to ascertain this property in stone taken from new quarries, before using it for important public works. Por 8. Porphyry. This stone is usually composed of compact feldspar, having crystals of the same, and sometimes those of other minerals, scattered through the mass. phyry furnishes stones of various colors and texture; the usual color being reddish, approaching to purple, from which the stone takes its name. One of the most beautiful varieties is a brecciated porphyry, consisting of angular fragments of the stone united by a cement of compact feldspar. Porphyry, from its rareness and extreme hardness, is seldom applied to any other than ornamental purposes. The best known localities of sienite and porphyry in the United States are in the neighborhood of Boston. 9. Green-stone. This stone is a mixture of hornblende with common and compact feldspar, presenting sometimes a granular though usually a compact texture. Its ordinary color, when dry, is some shade of brown; but, when wet, it becomes greenish, from which it takes its name. Greenstone is very hard, and one of the most durable rocks; but, occurring in small and irregular blocks, its uses as a building stone are very restricted. When walls of this stone are built with very white mortar, they present a picturesque appearance, and it is on that account well adapted to rural architecture. Green-stone might also be used as a material for road-making; large quantities of it are annually_taken from the principal locality of this rock in the United States, so well known as the Palisades, on the Hudson, for constructing wharves, as it is found to withstand well the action of salt water. 10. Granite and Gneiss. The constituents of these two stones are the same, being a granular aggregation of quartz, feldspar, and mica, in variable proportions. They differ only in their structure-gneiss being a stratified rock, the ingredients of which occur frequently in a more or less laminated state. Gneiss, although less valuable than granite, owing to the effect of its structure on the size of the blocks which it yields, and from its not splitting as smoothly as granite across its beds of stratification, furnishes a building stone suitable for most architectural purposes. It is also a good flagging material, when it can be obtained in thin slabs. Granite varies greatly in quality according to its texture and the relative proportion of its constituents. When the quartz is in excess, it renders the stone hard and brittle, and very difficult to be worked with the chisel. An excess of mica usually makes the stone friable. An excess of feldspar gives the stone a white hue, and makes it freer under the chisel. The best granites are those with a fine grain, in which the constituents seem uniformly disseminated through the mass. The color of granite is usually some shade of gray; when it varies from this, it is owing to the color of the feldspar. One of its varieties, known as Oriental granite, has a fine reddish hue, and is chiefly used for ornamental purposes. Granite is sometimes mistaken for sienite, when it contains but little mica. The quality of granite is affected by the foreign minerals which it may contain; hornblende is said to render it tough, and schorl makes it quite brittle. The protoxide and sulphurets of iron are the most injurious in their effects on granite; the former by conversion into a peroxide, and the latter, by decomposing, destroying the structure of the stone, and causing it to break up and disintegrate. Granite, gneiss, and sienite, differ so little in their essential qualities, as a building material, that they may be used indifferently for all structures of a solid and durable characThey are extensively quarried in most of the New England States, in New York, and in some of the other States intersected by the great range of primitive rocks, where the quarries lie contiguous to tidewater. ter. 11. Mica Slate. The constituents of this stone are quartz and mica, the latter predominating. It is principally used as a flagging stone, and as a fire stone, or lining for fur naces. 12. Buhr or Mill stone. This is a very hard, durable stone, presenting a peculiar, honeycomb appearance. It makes a good building material for common purposes, and is also suitable for road coverings. 13. Horn-stone. This is a highly silicious and very hard stone. It resembles flint in its structure, and takes its name from its translucent, horn-like appearance. It furnishes a very good road material. 14. Steatite, or Soap-stone. This stone is a partially indurated talc. It is a very soft stone, not suitable for ordinary building purposes. It furnishes a good fire-stone, and is used for the lining of fireplaces. 15. Talcose Slate. This stone resembles mica slate, being an aggregation of quartz and talc. It is applied to the same purposes as mica slate. 16. Sand-stone. This stone consists of grains of silicious sand, arising from the disintegration of silicious rocks, which are united by some natural cement, generally of an argillaceous or a silicious character. The strength, hardness, and durability of sand-stone vary between very wide limits. Some varieties being little inferior to good granite, as a building stone, others being very soft, friable, and disintegrating rapidly when exposed to the weather. The least durable sand-stones are those which contain the most argillaceous matter; those of a feldspathic character are also found not to withstand well the action of the weather. Sand-stone is used very extensively as a building stone, for flagging, for road materials, and some of its varieties furnish an excellent fire-stone. Most of the varieties of sand-stone yield readily under the chisel and saw, and split evenly, and, from these properties, have received from workmen the name of free-stone. The colors of sand-stone present also a variety of shades, principally of gray, brown, and red. The formations of sand-stone in the United States are very extensive, and a number of quarries are worked in New England, New York, and the Middle States. These formations, and the character of the stone obtained from them, are minutely described in the Geological Reports of these States, which have been published within the last few years. Most of the stone used for the public buildings in Wash |