04248597 is referenced by 27 patents and cites 11 patents.

A novel depletion indicator (time watch) for removable substances containing acid or basic groups is disclosed, together with a novel method of use therefor. The removable substance of a predetermined concentration comes into contact with a suitable pH color indicator that can change color at a predetermined pH range within a much larger measurable pH range, which color change occurs as the concentration of the removable substance diminishes by passing through a permeable film containing both the removable substance and the pH color indicator.The color change occurs at a predetermined time, e.g., the same time that the active ingredient has diminished to the point it is determined to be inactive.

Title
Time watch or depletion indicator for removable substances
Application Number
5/968871
Publication Number
4248597
Application Date
December 12, 1978
Publication Date
February 3, 1981
Inventor
Gerald W McNeely
Arden
NC, US
Agent
Francis W Young
Charles A Wendel
Robert H Falk
Assignee
Akzona Incorporated
NC, US
IPC
G01N 21/06
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