Paul;

If I understand the set-up of your water manometer, the addition of
detergent would do little to help with surface tension issues.  I

believe

that what Al might have been referring to are the effects of adhesion

and

cohesion of water within the tubes.  This would be less of a factor with
larger diameter tubes.  OTOH, I believe that the design of the manometer
would result in these effects cancelling each other out (if they even

exist)

due to the water moving different directions in the tubes.

Take care, Marc M

Tom Kendall opined:

If I remember correctly, some manometers use a water/alcohol mix to reduce
this tendancy.  Probably any alcohol will work (rubbing, ethyl, methyl...).
Something to do with surface wetting, surface tension, etc.  May be a cheap
solution.

On the other hand, I would think a surfactant (like detergent) would make
the meniscus so drawn out that it would be hard to see/read unless it was a
large diameter tube (not to mention foaming if there is any vibration).  No
theoretical basis, just a gut feel.

Well it is not really necessary. I was just curious about the detergent.
As it is now it is really easy to read.

Paul Lamar
 
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