Place a piece of window glass flat on the table, pour a little kerosene on the spot to be bored, clasp the file near the end, press the end down hard on the spot and turn it back and forth with a gouging motion (Fig. 87). You twist the file just as you would twist an awl to force it into hard wood. You will soon penetrate the surface; use plenty of kerosene and continue the boring until you are nearly through; then turn the plate over and start a hole on the other side to meet the one you have made. [Illustration: FIG. 87 BORING A HOLE IN GLASS ] Do not rush things; it will take you ten or fifteen minutes to bore through ordinary window glass. Bore a hole in a bottle in the same way, except that the boring is all from the outside. If the end of the file becomes dull, break off a small piece, with a pair of pliers, to expose a fresh surface. Experiment 67. To cut a bottle in two. [Illustration: FIG. 88 BOTTLE READY TO BE CUT IN TWO ] Wind a strip of blotting-paper or wrapping paper 2 inches wide around the bottle at one side of the line along which you wish to cut. Make three or more thicknesses and then tie the paper with cord within ½ inch of the edge to be cut. Wrap another similar piece on the opposite side of the place to be cut and ³⁄₁₆ inch from the first piece (Fig. 88). [Illustration: FIG. 89 HEATING THE BOTTLE ] Now stand the bottle in a pail of water until the paper is thoroughly wet (about five minutes), take it out, rotate it in a horizontal position and direct the blowpipe flame against the glass between the papers (Fig. 89). Continue this for four or five minutes, then if the bottle has not dropped apart, plunge it vertically into the pail of water. The bottle will break into two parts along the line between the two papers (Fig. 90). If it does not do so, repeat the operation until it does. Smooth the rough edges outside and inside with the file. You cannot do this with the flame because the glass is too brittle. [Illustration: FIG. 90 THE BOTTLE CUT IN TWO ] Experiment 68. To grind glass. Rough edges of glass can be ground smooth by means of emery paper. For example, to smooth the edges of the glass bottle you have just cut in two, use the file for the rough work, then lay a piece of emery paper on a plate of glass, emery side up, pour a little kerosene on it and rub the rough surface on the emery with a rotary motion (Fig. 91). Finish with fine emery paper, and smooth the edges inside and out with the fine paper. [Illustration: FIG. 91 SMOOTHING THE EDGES ] Experiment 69. To cement glass. There are two important points to remember in cementing glass: first, to get the glass clean, and second, to press the surfaces together after applying the cement, to squeeze out as much of the cement as possible, and to keep them pressed together until the cement is hard. To clean the glass wash it thoroughly with soap and water, rinse, and dry with a clean cloth. [Illustration: FIG. 92