The prime conductor is formed from a piece of curtain-pole two inches in diameter and eight inches long. The ends are rounded with a rasp and then smoothed with sandpaper. The whole surface is then shellacked and covered with a layer of tinfoil. The heads of a number of dressmaker’s pins are cut off, and the pins forced into the side of the prime conductor with a pair of pincers. They should form a row like the teeth of a rake about three-eighths of an inch apart. A hole is bored in the center of the under side of the prime conductor to receive a glass rod one-half inch in diameter. A second hole of the same size is bored in the base in such a position that when the glass rod is in place, the teeth on the prime conductor are on a level with the axis of the bottle, and their points about 3-32 of an inch away from the glass. The glass rod must be used in order to insulate the prime conductor and prevent the escape of the electricity. It is secured with some of the cement described on page 33. A piece of water-gauge glass may be used in place of a glass rod.
Fig. 32.—The Prime Conductor or Collector.
A strip of oiled silk, or in its place a strip of silk which has been shellacked, eight or nine inches wide, and long enough to reach half-way around the bottle, is tacked to the rubber so that the silk covers the upper half of the cylinder and comes over to within one-quarter of an inch of the steel points.
The machine is now complete, and when the handle is turned rapidly, you will be able to draw sparks from the prime conductor. The sparks will probably be very short, about one-half of an inch long. These can be increased, however, to three inches, if the glass is of the right quality, by treating the rubber with amalgam.
The amalgam is formed by melting one ounce of tin and adding to it one ounce of zinc in small bits. As soon as the zinc has also melted add to the mixture two ounces of mercury which has been previously warmed. Be careful not to inhale any of the vapor during this operation. Pour the mixture into a vessel of cold water, which will reduce the metal to small grains. Pour off the water and grind the amalgam to a powder by pounding the grains with a hammer.
The leather rubber should be thinly smeared with lard and the powdered amalgam rubbed on it.
In order to obtain the greatest effect from an electric machine, it must be carefully freed from dust and particles of amalgam adhering to the glass, and the insulating column rubbed with a warm woolen cloth. The best results are obtained by placing the machine near a stove or radiator where it is warm.
Fig. 33.—The Complete Cylinder Electric Machine.