The presence of vegetable albumen in tim ber appears to be the primary cause for its deterioration. The most necessary element in the healthy growing tree, it is the most per nicious of all in that which is dead. The sap wood contains a large proportion of it and other fermentable elements, the putrefaction of which .cause dry-rot or sap-rot, and pro duce various forms of injurious fungi, there fore, in order to correct these evils, the most effective method to preserve timber is to expel or exhaust its fluids, solidify its albumen and introduce an antiseptic liquid. This appears to be accomplished in the most satisfactory manner by the process introduced by Robbins in 1865, by which the liquids are dissipated and the albumen solidified by heating the wood in a chamber raised to a temperature of 212° F., and then subjecting it to the vapor of coal tar, resin or bituminous oils, which,' being at a temperature of not less than '325° F., will readily take the place of the vapor expelled by the lower temperature.
Stone.—To be suitable for building pur poses, it is essential that a stone should pos sess the qualities of durability, permanency of color, strength and toughness, and should be susceptible of being inexpensively quarried, and easily worked. The greater number of such stones belongs to some one of the fol lowing classes of rocks: (1) The crystalline; (2) the calcareous; and (3) the fragmental rocks, including the sandstones and slates.
Of the crystalline rocks, the best known and the most suitable are the granites and the syenites, which possess an average crushing strength of from 15,00 to 26,200 pounds per square inch; most of them above 20,000 pounds. These stones, varying greatly in their physical composition and color, are found in large quan tities in all parts of the world. They are very proof against the action of frost, and are com monly quite permanent in color, varying from a sparkling whitish gray to dark gray, and from a delicate pink to a dark red. Until recently, on account of great hardness, granite was only employed for massive masonry in which roughly dressed stones could be appropriately used, or where the magnitude of the structures per mitted the great se involved in dressing and polishing; but the development of improved forms of stone-cutting and dressing machinery during the last few years permits of its being turned and carved into columns, pilasters and other forms, and polished perfectly, at a com paratively small expense, so that it is being used more and more extensively, and is be coming one of the most popular of all building stones.
Although quarried in practically every East ern State embracing the Appalachian Moun tain system, from Maine to North Carolina, and in the States of California, Montana, Wy oming, Colorado, Minnesota, Wisconsin and Missouri, the greatest supply of granite in the United States is furnished by Maine and Mas sachusetts. The Maine granites, principally derived from the Hurricane Island quarries, are mostly of the light gray variety, although a limited amount of the pink and red varieties are also quarried and are found to be commer cially available. The Massachusetts granites
are of a rich dark blue-gray color, and are extensively quarried in the vicinity of Quincy, while other fine granites of similar qualities are quarried at Concord, N. H., and Westerly, RI.
While the United States is one of the largest producers of granite, it is also one of its largest importers. Red granites from the quar ries at Peterhead, Scotland, and the gray granites from Aberdeen are quite largely brought into this country for monumental work. They take a very high polish, and are of durability, especially the coarse red variety. This is also the case with the red and gray Canadian granites, which are exten sively quarried in Quebec, New Brunswick, Nova Scotia, Ontario, and near Victoria, in British Columbia. In the United States, be sides granite and syenite, the other, crystalline rocks available to some extent for building purposes are porphyry, gneiss and trap. Por phyry, although a very handsome building stone, with large crystalline structure, and colors ranging through shades of white, gray, pink, red and black, is used only to a limited extent in rough construction on account of its great hardness, and the consequent difficulty of cutting and polishing it within a reasonable limit of expense. Gneiss is more extensively used; it resembles granite in composition, but, unlike granite, it has a well-defined cleavage, i which allows it to be split into thick slabs. Trap is a sombre-hued rock, which is very difficult to work, and is seldom used as a material of construction, except in the form of paving blocks, or as crushed stone for making concrete or road material.
Of the calcareous rocks, the most suitable for structural purposes are the limestones and the marbles. These consist of carbonate of lime, and differ in quality rather than in com position, the marble having a crystalline struc ture capable of taking a high polish. The oolitic limestones, possessing great strength, their re sistance to compression ranging from 4,500 pounds up to 20,600 pounds per square inch (the strongest being those from Arkansas and Vermont), are in grei.t favor because of their fine and even texture. The most widely known in the United States are those quarried in Indiana and Kentucky, from strata of Mis sissippian (Sub-Carboniferous Age), and com monly known as °Bedford Stone"; they are handsome in color and are very easily worked. The colors of limestones range through broken shades of pink, red, yellow, green and blue, imparted to the structure by various impurities. Dolomitic limestone, commonly known as do lomite, contains magnesia in addition to the carbonate of lime; is somewhat coarse in qual ity, and is quarried in nearly every State of the Union, to supply an apparently permanent local demand. The most favorably known of the foreign varieties is that obtained from the quarries of the Isle of Portland, England, and the French stones quarried near Caen. Nor mandy. The latter is a soft, fine-grained stone of a light color very suitable for carved work, but entirely unfitted for exposed structures in cold climates, on account of its highly absorb ent quality.