Patent ID: 7302846

Claim:
A method for determining the level of a foamable fluid in a container comprising: obtaining a container having an outlet for a first fluid and an inlet for a second fluid; said container having a first fluid region therein; a first fluid being present at an original level in said first fluid region of said container; said container, for when in use, having said first fluid at least partially removed from said container thereby forming a second fluid region; placing on at least one exterior surface of said container at least one temperature-measuring device operating at a single discrete temperature in the range of 45° F. to 80° F.; at least one said temperature-measuring device being located in a region of said container where said second fluid region is formed by removal of said first fluid; initially observing a first temperature in said first fluid region of said container when said first fluid is present in said first fluid region of said container; subsequently observing a second temperature in said second fluid region of said container after a portion of said first fluid has been removed; correlating the difference between said first temperature and said second temperature to the level of said first fluid in said container; and, provided further that the temperature measuring device is based on a member selected form the group consisting of a leuco dye, a clearing point liquid crystal, cholesteric liquid crystal, chiralnematic liquid crystal, and mixtures thereof.