Non-conductors
When working in different materials that seem adapted to electrical apparatus, it is necessary to know whether they can be used safely or not. Often a material seems to be just the thing, but if it should be a partial conductor, when a non-conductor is desired, it would be hazardous to use it. A list of non-conductors is therefore valuable to the amateur. Some of the principal non-conductors, among the many, are as follows: glass, porcelain, slate, marble, hard stone, soapstone, concrete (dry), hard rubber, soft rubber, composition fibre, mica, asbestos, pitch, tar, shellac, cotton, silk; cotton, silk and woollen fabrics, transite (dry), electrobestus (dry), duranoid; celluloid, dry wood (well seasoned), paper, pith, leather, and oil.
While this account of formulæ and material might be extended, this is not necessary inasmuch as the formulæ and practical directions which have been given will answer all usual practical requirements.
Insulating Varnish
There are several good insulating varnishes that can be used in electrical work, the most valuable being shellac dissolved in alcohol and applied with a brush. To make good shellac, purchase the orange-colored flake shellac by the pound from a paint-store, place some of it in a wide-necked bottle, and cover it with alcohol; then cork the bottle and let it stand for a few hours. Shake the bottle occasionally until the shellac is thoroughly dissolved. It can be thinned by adding alcohol. Always keep the bottle corked, taking out only what is necessary from time to time.
Another varnish can be made by dissolving red sealing-wax in alcohol and adding a small portion of shellac. This can be applied with a soft brush, and is a good varnish. When colors are to be applied to distinguish the poles, red is used for the positive current-poles and blue or black for the negative, if they are colored at all.
A very good black varnish is made by adding lampblack to shellac; another consists of thick asphaltum or asphaltum varnish. This is waterproof, and dries hard, yet with an elastic finish.
Battery Wax
For the upper edges of glass cells, such as the Leclanché or other open-circuit batteries, there is nothing superior to hot paraffine brushed about the upper edge to prevent the sal-ammoniac or other fluids from creeping up over the top. The paraffine can be colored with red-lead, green dust, or powders of various colors if desired, but generally the paraffine is used without color, so that it has a frosted-glass appearance when it is cool and dry.
A black wax for use in stopping the tops of dry cells and coating the tops of carbons is composed of paraffine, eight parts; pitch, one part; lampblack, one part. Heat the mixture and stir it until thoroughly mixed; then apply with a brush, or dip the parts into the warm fluid.