INSULATION
Electric Insulation:
Insulating Varnishes.
I.—Melt 2 parts of asphalt together with 0.4 parts of sulphur, add 5 parts of linseed-oil varnish, linseed oil or cottonseed oil, keep at 320° F. for 6 hours; next pour in oil of turpentine as required.
II.—Maintain 3 parts of elaterite with 2 parts of linseed-oil varnish at 392° F. for 5 to 6 hours; next melt 3 parts of asphalt, pour both substances together, and again maintain the temperature of {426} 392° F. for 3 to 4 hours, and then add 1 part of linseed-oil varnish and oil of turpentine as required.
III.—Insulating Varnish for Dynamos and Conduits with Low Tension.—Shellac, 4 parts; sandarac, 2 parts; linoleic acid, 2 parts; alcohol, 15 parts.
IV.—An insulating material which contains no caoutchouc is made by dissolving natural or coal-tar asphalt in wood oil, adding sulphur and vulcanizing at 572° F. The mixture of asphalt and wood oil may also be vulcanized with chloride of sulphur by the ordinary process used for caoutchouc. Before vulcanizing, a solution of rubber scraps in naphthalene is sometimes added and the naphthalene expelled by a current of steam. Substitutes for hard rubber are made of natural or artificial asphalt combined with heavy oil of tar and talc or infusorial earth.
Most of the insulating materials advertised under alluring names consist of asphalt combined with rosin, tar, and an inert powder such as clay or asbestos. Some contain graphite, which is a good conductor and therefore a very undesirable ingredient in an insulator.
Insulation Against Heat.
An asbestos jacket is the usual insulator for boilers, steampipes, etc. The thicker the covering around the steampipe, the more heat is retained. A chief requirement for such protective mass is that it contains air in fine channels, so that there is no connection with the closed-in air. Most substances suitable for insulating are such that they can only with difficulty be used for a protective mass. The most ordinary way is to mix infusorial earth, kieselguhr, slag-wool, hair, ground cork, etc., with loam or clay, so that this plastic mass may be applied moist on the pipes. In using such substances care should be taken carefully to clean and heat the surfaces to be covered. The mass for the first coating is made into a paste by gradual addition of water and put on thick with a brush. After drying each time a further coating is applied. This is repeated until the desired thickness is reached. The last layer put on is rubbed smooth with the flat hand. Finally, strips of linen are wound around, which is coated with tar or oil paint as a protection against outside injuries. Cork stones consist of crushed cork with a mineral binding agent, and are sold pressed into various shapes.
Leather Waste Insulation.
Insulation Against Moisture, Weather, Etc.
Experiments have shown that with the aid of red lead a very serviceable, resistive, and weatherproof insulation material may be produced from inferior fibers, to take the place, in many cases, of gutta-percha and other substances employed for insulating purposes, and particularly to effect the permanent insulation of aerial conductors exposed to the action of the weather. Hackethal used for the purpose any vegetable fiber which is wrapped around the conductors to be insulated. The fiber is then saturated with liquid red lead. The latter is accomplished in the proportion of 4 to 5 parts of red lead, by weight, to 1 part, by weight, of linseed oil, by the hot or cold process, by mere immersion or under pressure. All the three substances, fiber, oil, and red lead, possess in themselves a certain insulating capacity, but none of them is alone of utility for such purposes. Even the red lead mixed with linseed oil does not possess in the liquid state a high degree of insulating power. {427} Only when both substances, the ingredients of the linseed oil capable of absorbing oxygen and the lead oxide rich in oxygen, oxidize in the air, a new gummy product of great insulating capacity results.
INTENSIFIERS: See Photography.