Variable electric resistance

Abstract

314,306. Howards & Sons, Ltd., and Bandli, M. June 24, 1929. [A Specification was laid open to inspection under Sect. 91 of the Acts, June 24, 1929]. Resistance materials.-A material for a variable resistance is made by suspending a finely subdivided conductor other than carbon in a fluid binding-agent which is a non-conductor and is capable of setting, the proportion of the conductor being such that the final product will contain more of the conductor than of the non-conductor, and causing the binding-agent to set before segregation of the conductor occurs. Suitable binding-agents are those which tend to contract when giving up a solvent by evaporation, or on cooling or otherwise setting. Examples are cellulose esters or ethers, particularly cellulose acetate or nitrate and viscose, rubber, guttapercha, lacquer, natural or synthetic resins, glues, gelatin, dextrin, albumin, casein. These may be dissolved in water or a volatile solvent. Finely subdivided fibres such as agar-agar, suspended together with the conductor in water or a volatile solvent are in some cases sufficiently binding. The conductor may be a metal such as iron or nickel reduced from the oxide without fusion. Other metals and alloys or solid amalgams may be used, also oxide or oxidized ores, many minerals, and some crystals. Two or more conductors may be mixed. A volatile solvent containing metal in the colloidal state may be used, or the solvent for the colloidal solution may be used in conjunction with the solvent for the binding-agent. It is generally necessary to add finely-divided reduced metal to make up the complement of metal. Pressure may be applied during evaporation or solidification. As an example 1 part by weight of cellulose acetate is dissolved in 10 parts of acetone and the solution mixed with 11 parts of iron which has been reduced from ferric oxide by heating in hydrogen. During the mixing, part of the acetone is allowed to evaporate. The resulting viscous liquid is then poured on to a glass plate and allowed to evaporate completely. Specification 273,025 is referred to.

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