Re-pressed Brick weighs about 150 lb. per cubic foot, common brick 125, inferior soft 100. ComMon bricks will average about 411b. each.
Hollow Brick, used for interior walls and furring, are usually of the following dimensions: Single, 8 in. long, ai in. wide, 21 in. thick. Double, 8 " " 71 " " 41 " " Treble, 8 " " " " 71 " " Roman Brick, 12. in. long, 4. to 41 in. wide, 11 in. thick.
Specific Gravity, Weight, and Resistance to Crushing of Brick.
— — I Resistance to Designation of brick. Specific gravity. Weight per cubic foot, pounds. Crushing. pounds per sq. in.
• Best pressed. 2 . 4 150 5,000 to 14,973 Common hard; 1.0 to 2.0 125 5,000 to S,000 'oft . . 1 .4 100 450 to 000 • .
are used wherever high temperatures are to be resisted. They are made from fire-clay by processes very similar to those adopted in making ordinary brick. Fire-clay is also used in the manufacture of paving-blocks or pavers, especially in West ern Indiana; and many of the streets of our Western cities are laid with fire-clay block, forming a smooth and durable roadway.
Fire-clay may be defined as native combinations of hydrated silicates of alumina, mechanically associated with silica and alumira in various states of subdivision, and sufficiently free from silicates of the alkalies and from iron and lime to resist vitrification at high tem peratures. The presence of oxide of iron is very injurious; and, as a rule, the presence of 6 per cent justifies the rejection of the brick. The. presence Of 3 per cent of combined lime, soda, potash, and mag nesia should be a cause for rejection. The sulphide of irom—pyrites —is even worse than the substances first named.
A good fire-clay should contain from 52 to SO per cent of silica and 1S to 35 per cent of alumina and have a uniform texture, a some what greasy feel, and be free from any of the alkaline earths.
Good fire brick should be uniform in size, regular in shape, homogeneous in texture and composition, strong, and infusible and break with a uniform and regular fracture.
A properly burnt fire-brick is of a uniform color throughout its mass. A dark central patch and concentric rings of various shades of color are due mainly to the different states of oxidation of the iron and partly to the presence of unconsumed carLonaeeous mat ter, and indicates that the brick was burned too rapidly.
Fite-brick are made in various forms to suit the required work. A straight brick measures 9 X 41 X 2-", inches and weighs about 7 lb.
or 120 lb. per cubic foot; specific gravity 1.93. One cubic foot of wall requires 17 9-inch bricks; one cubic yard requires 460. One ton of fire-clay should be sufficient to lay 3000 ordinary bricks. English' fire-bricks measure 9 X X 2} inches.
To secure the best results fire-brick should be laid in the same clay from which they are manufactured. It should be used as a thin paste, and not as mortar: the thinner the joint the better the furnace wall. The brick should be dipped in water as they are used, so that when laid they will not absorb the water from the clay paste. They should then receive a thin coating of the prepared fire-clay, and be carefully placed in position with as little of the fire clay as possible.
CEnENTING FIATERIALS.
Composition. All the cementing materials employed in build ings are produced by the burning of natural or artificial mixtures of limestone with clay or siliceous material. The active substances in this process and the ones which are necessary for the production of a cement, are the burned lime, the silica and the alumina, all of which enter into chemical combination with one another under the influence of a high temperature.
Classification. Owing to the varying composition of the raw materials, which range from pure carbonate of lime to stones contain ing variable proportions of silica, alumina, magnesia, oxide of iron, manganese, etc., and the different methods employed for burning, the product possesses various properties which regulate its behavior when treated with water, and render necessary certain precautions in its manipulation and use, and furnishes a basis fcl- division into three classes; namely, common lime, hydraulic and hydraulic cements, the individual peculiarities of which will be taken up later.