Importance

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Abstract

A time-lapse indicator in which an electrically conducting, fluid-absorbent layer is initially separated from an activating fluid. When the indicator is activated the fluid flows into the absorbent layer, thereby changing the electrical conductivity of the absorbent layer. The fluid may be retained by a receptacle having a rupturable wall portion in a layer paralleling said absorbent layer and the rupturable wall portion may be a frangible layer between the liquid and the absorbent layer, which is broken when the indicator is activated. A time delay layer may also be included between the frangible layer and the absorbent layer to control the rate of flow of the liquid into the absorbent layer and thereby prolong the effective operation of the indicator following activation thereof.

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First Claim