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I need to precisely measure the internal volume of an open steel fixture. I was planning to do this via displacement, but I'm wondering what the best fluid would be. Ideally it should have no surface tension so that it readily penetrates every facet of the fixture. It would also be convenient if it was non-wetting which (if I understand that term correctly) means that it would not adhere to the steel when removed.

One suggestion I heard was to use water-soluble cutting fluid. Are there any other readily-available fluids with these characteristics, or well suited to this application?

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    $\begingroup$ Use water, distilled if you are afraid, and don't care. It wont damage steel if the exposure is brief. To reduce effects of surface tension, wash the fixture with acetone before several times, while working in washed gloves. Water wets steel, so the problem is to remove traces of fat from hands. $\endgroup$ – permeakra Nov 1 '14 at 21:05
  • $\begingroup$ Not worried about brief effects on the steel, and I can completely degrease everything with acetone. But as you note that doesn't solve the surface-tension problem with water, right? $\endgroup$ – feetwet Nov 1 '14 at 23:16
  • $\begingroup$ @permeakra: Actually, is there any reason to not mix a little soap (surfactant) into the water to eliminate the surface tension and its associated problems? $\endgroup$ – feetwet Nov 6 '14 at 14:19
  • $\begingroup$ There is not problem with it. However, since water wets steel, the only problem is to get rid of bubbles trapped inside. $\endgroup$ – permeakra Nov 6 '14 at 14:35
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For a very precise volume measurement, you might want to consider using mercury because of its high density. (You would actually measure the weight of the fluid.)

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  • $\begingroup$ But doesn't mercury have high surface tension? Or is its weight enough to force it into every crevice, so one only has to worry about the meniscus? $\endgroup$ – feetwet Oct 2 '14 at 19:31
  • $\begingroup$ I'm not sure I'd want to hang around a large bath of mercury. Not to mention possible corrosion issues after contact between the steel and mercury. Go with water, wipe down afterwards with methanol... $\endgroup$ – Jon Custer Oct 2 '14 at 19:57
  • $\begingroup$ @JonCuster Mercury is transported in steel containers. $\endgroup$ – permeakra Nov 1 '14 at 20:59
  • $\begingroup$ @permeakra - Good catch - unlikely to be dipping hot steel into a mercury bath. Now just don't go dipping aluminum into gallium... $\endgroup$ – Jon Custer Nov 3 '14 at 15:25

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