Of course, the first consideration in building a house is the preparation of the foundations, which are formed in various ways, according to the nature of the soil on which they are laid; unless the ground itself is firm enough to receive the walls, sometimes thick layers of concrete (a sort of mortar) is used, sometimes layers of planking are put down, or even cross beams of timber, and in some cases, where the earth is very loose and damp, timber piles are driven into it on which to lay the foundation. The foundation once laid, the vaults or cellars are built either in the ordinary way, or in a series of arches of various forms; then follow the abutments, the wing-walls, the main-walls, with iron “Bressumers” for supporting those parts of the walls which are above large openings like great doors or shop fronts. The partitions, or interior walls, may be either solid brick or stone, or may be constructed entirely of timber, or they may be frames of timber filled in with masonry or brickwork. Then come the floors, the roofs and roof-coverings, and finally the ceilings and the doors and windows. The materials used in building are principally timber, stone, slate, bricks, tiles, mortar, lime, cement, iron, glass, lead, zinc, colours and varnishes. Those with which the working bricklayer has most to do are bricks, slates, tiles, stonework, cement, and mortar, for these are principally used in making walls and roofs, which is the greater part of his trade. The stone and slate come from the quarries, and we have already seen how bricks are made. Mortar is made in the following way. 1st. The soft chalky stone known as limestone, is calcined or burnt, by exposure to strong heat in a lime kiln; the heat drives off a gas which is contained in it (called carbonic acid gas), and leaves it in a state in which it is known as quick-lime. 2d. The quick-lime is “slaked,” by pouring water upon it, when it swells and becomes very hot, afterwards falling into a fine powder. 3d. This powder is mixed into a rather stiff paste, more water is added, and when a certain quantity of sand is added becomes _mortar_, and may be used for cementing bricks together. Concrete is made by mixing gravel, sand, and ground unslaked lime together with water; it is used for foundations, and filling in apertures requiring strength and firmness. Iron is used by the builder in two different states, as cast iron and wrought iron; the _girders_ for supporting roofs and walls are mostly cast in moulds (_see Iron Founder_), though both these and other parts of the ironwork used in building, are frequently of iron wrought by hand. Lead is used by the mason for securing and coating the iron clamps which hold the blocks of stone together; it is also used in the plumbers’ work of a house (_see Plumber_). Zinc is used in the manufacture of gutters, pipes, and portions of roofs. [Illustration: Trowel.]