Cooking Thermometer: Candy Thermometer in a Glass Tube with a Venting Plastic Cap (Chaney, US 3,636,769, 1972)

A candy and deep-fat thermometer that clips to the side of a pan. A glass thermometer on a printed scale card sits inside a protective glass tube, so it never touches the candy. The top of the tube is closed by a polyethylene cap that seals in normal use but softens when the whole thermometer is heated far too hot, as in an oven, so the air inside escapes instead of bursting the tube. Result: a pan-side cooking thermometer that cannot explode if overheated. Source: J. L. Chaney, US 3,636,769 (1972). Unknown: the scale range, sizes and several materials. Picture: the patent drawing.