Nikola Tesla Books
OSCILLATION TRANSFORMERS 53 Space turns Fig. 7. The turns of wire in the secondary should be spaced to provide adequate insulation for the extremely high potential separated from the secondary. The case or container for the coils may be of wood, lined with zinc. The cover, of course, must be of some good insulating material such as glass, hard rubber or marble. Slate should not be used as the minute metallic veins found in some varieties will be ruinous to the output of the coil. The high potential leads from both primary and secondary may be brought up through porcelain, glass, or hard rubber insulators attached to the top of the case and extending down into the oil. The compound of equal parts of beeswax and rosin previously mentioned is used to seal in the pancake coils of portable electro-therapeutic outfits where every effort must be expended in the direction of light weight and compactness. This compound is melted up in a double boiler, as the insulating properties are ruined if the mixture is permitted to scorch. The pancake coil, which is specifically described later in this book, is immersed in the hot compound and permitted to remain for hours until the windings and the paper separating layers are thoroughly impregnated with the molten wax. The advantages of the close coupling of primary and secondary made possible through the use of some better insulator than air are found in the greater efficiency of the oscillation transformer constructed in this way. The spark is thicker and hotter, as well as being of the desired length.
