Over a weak fire heat a bottle of linseed oil, with an ounce of litharge, and a small portion of minium, till such time as a feather, used in stirring it, shall be burnt to the degree of being easily rubbed to powder between the fingers. Then take off the varnish, let it cool, clarify it from any impurities which may have fallen to the bottom, and heat it again. Having, in the mean time, melted from three to four ounces of pitch, mix this with the warm varnish. The specific gravity of the pitch hinders it from mingling thoroughly with the varnish, though it even remain so long upon the fire as to be evaporated to considerable thickness. It is not till the varnish be cooled, nearly to the consistency of common syrup, that this effect takes place in the requisite degree. If it be too thick, let hot varnish be added, to bring it to the proper consistency; if it be too thin, add melted pitch. Next, put in as much brick-dust as the mixture can receive, without being made too thick for convenient use. The finer the brick-dust, and the easier it is to be moved with the point of a pencil, so much the fitter will it be to fill up the chinks and unevenness of the bricks, and, as it were, to incorporate itself with their substance. Prepare the brick-dust in the following manner:--Take a certain number of pieces of good brick, beat them into dust, and sift the dust in a hair-sieve. Then, to improve its fineness, rub it on a stone with water, dry it, and mix it with the varnish in the necessary proportion. If the brick-dust be naturally of too dark a color, a portion of some that is brighter may be added, to make the color clear. It is to be laid on the tiles in the same manner in which oil-colors in general are put upon the substances on which they are applied. The composition must be heated from time to time, when it is to be used. 1145. _Economical Method of employing Tiles for the Roofs of Houses._--A French architect (M. Castala) has invented a new method of employing tiles for the roofs of houses, so as to save one half of the quantity usually employed for that purpose. The tiles are made of a square instead of an oblong form; and the hook that fastens them is at one of the angles, so that, when fastened to the laths, they hang down _diagonally_, and every tile is covered one-fifth part on two sides by the superior row.