Abstract: A composition having regulated occurrence of opacity and clarity at selected temperatures; method of making and using such a composition to create a temperature-indicating device by filling the composition in a suitable container of transparent material and having a background in the form of a color, a letter or a number i.e., in order to be able to visually interpret the difference between opacity and clarity. A reversible indicating device is made which can show if the upper or lower limits of a pre-set temperature interval has been exceeded or fallen below.

Abstract: PH indicator composition has controlled change of color at a selected sub-freezing temperature. The composition comprises at least one pH indicator, a buffer solution containing at least one inorganic ion in solution and a control agent or a precursor of a control agent. The buffer solution has a pH capable of changing when the temperature of the buffer solution is lowered to below freezing. The control agent is capable of effecting a change in ionic strength and proton composition of the frozen pH indicator composition to thereby control the temperature at which the color change occurs. A method of using the composition comprises lowering the temperature from a first temperature above freezing to a second temperature at which the pH indicator composition is in a substantially frozen state. The composition is particularly useful in a color change thermometer.