A petroleum or synthetic grease is used to protect electrical apparatus from overheating. The grease is applied to a portion of an electrical apparatus which is exposed to a gas stream, particularly to portions subjected to operating temperatures of about 100.degree. C. When the coated portion of the electrical apparatus overheats the grease forms particles in the gas stream which are detected by a monitor. The apparatus can then be shut down or its load reduced.

Heat-recoverable articles carrying a "thermochromic" composition comprising organic materials which melt and decompose to provide a color-change indicating that the articles have been heated to a certain temperature, e.g. to melt a sealant carried on the surface of the article which is to contact a substrate around which the article is to be shrunk. Mixtures of relatively simple compounds may be used to graduate the color change, and means are described for preventing reversion to the original color on long-term exposure to moisture.

An abnormal condition detector detects an abnormal condition of an electric apparatus by sampling an insulating fluid filled in the electric apparatus under a pressurized condition and detecting a change of the condition of an indicator induced by an acidic gas in the sampled insulating fluid.

A temperature indicating composition is provided for use on a recoverable article so that heating to produce recovery or to activate a heat-activatable sealant can be monitored. The composition comprises a thermochromic colorant in a binder that can be cured by UV radiation. Such a composition can be applied rapidly to polyolefin substrates by printing.

Injection molding of liquid epoxy resins is facilitated by adding an organic acid plus a siliceous filler to the curable epoxy resin system which thickens and thereby precludes leaking of resin from the mold.