EXPERIMENT 170. Magnetic figures.
415. Directions. (A) Arrange the apparatus and connections as in [Exp. 166], and make the magnetic figure of this combination as directed in [Exp. 168]. In this case the poles are alike. Sketch and study the results.
EXPERIMENT 171. Magnetic figures.
416. Directions. (A) Arrange apparatus and connections as in [Exp. 167], and make the magnetic figure of the combination as directed in [Exp. 168]. Compare the figure produced with that of [Exp. 168]. In this case the current passes through but one coil.
417. Permanent Magnetic Figures can be made in several ways for future study and comparison.
(A) Paraffine paper figures. Make paraffine paper as directed in Apparatus Book, page 135. For this purpose smooth, stiff, white paper is best, so that the filings will show plainly, and but a thin coating of paraffine should be given. Place the magnets upon the table, lay over them a piece of unparaffined paper, and fix the paraffine paper directly over this. This is necessary, as the coated paper sticks when heated. For electromagnets it will be necessary to support the edges of the paper with books, etc. Sprinkle on the filings and tap the paper to make them arrange themselves while the circuit is closed. After the lines of force show plainly, the current need not be used again, provided the paper be kept perfectly still. Pass the flame of a Bunsen burner over the paper to melt the coating. This will, no doubt, make the two pieces of paper stick together, and permanently fix the particles of filings in place. Do not heat the paper too much—just enough to melt the paraffine. If you have no gas, hold a fire-shovel, containing hot coals, over the paper. As soon as the paraffine cools, the figures will stand considerable handling.
Blue print figures are very pretty, and last indefinitely. Get some blue-print paper at a photographer's, who will give you directions about "developing" it with water. Keep this in the dark, and take out but one sheet at a time for experiments. To make the figures, take your apparatus near a window where bright sunlight comes in. Pull down the curtain so that you have but a dim light when you make the magnetic figure, as directed before. After the lines of force show plainly, raise the curtain, and let the bright sunlight shine on it for 5 or 6 minutes, or until the surface of the paper has a rich, bronze color. The paper cannot be acted upon by the light under the particles of filings. Quickly shake the filings from the paper, and wash it in 3 changes of water to "develop" it, then pin the paper up to dry.
EXPERIMENT 172. Lifting power.
418. Directions. (A) Arrange the apparatus as in [Exp. 164]. Hold an iron strip (No. 76), a screw-driver, or other iron bar directly over and near the poles of the experimental electromagnet. Close the circuit at the key, then lift the magnets by the "armature," as the iron strip may be called, the circuit being kept closed for a few seconds. If your cell is good there should be no trouble in lifting the magnets by the armature. Open the circuit, and see whether the magnets drop.
(B) Hold the magnets upside down directly over nails, tin boxes, iron filings, or other pieces of iron. Close the circuit, move the attracted iron to another place on the table, and open the circuit. Can this principle be used for practical purposes?