Measuring Surface Tension without Tensiometer?

Q. Is there any way to “eyeball” surface tension to see if it’s dropping when roughly measuring concentration or bath life?  

A. To numerically measure surface tension, you need a tensiometer and this is the recommended method. Tensiometers come in many varieties including Goniometer, Du Noüy Ring, Wilhelmy Plate and Bubble Pressure. Having one of these for measuring surface tension is essential.

However, we understand the occasional need to get a crude indication that surface tension lowering. Let’s use Alconox® Powdered Precision Cleaner as an example. Compare a water droplet without detergent with a water drop that has a 1% Alconox solution. The comparison should be done on a flat, unscratched surface. 

A solution with lowered surface tension will be flatter and spread wider than a normal drop of pure water. In the picture shown here, the water drop (left) is about 5 mm wide and the Alconox drop (right) is about 6 mm wide. You can also see that the edges of the Alconox drop are more flat and wide spread than the water drop, which is taller and has a lower angle than the Alconox drop.

This indicates that there is lower surface tension in the Alconox droplet. 

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