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Q & A: liquid for a gas handling system

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Most recent answer: 10/22/2007
Q:
HI, iím attempting to find the right liquid to use in my gas handling system. The liquid needs to be very low in volatility, so it does not contaminate the sample of gas with its own vapours. It needs to be low in viscosity, so that it does not trap tiny bubbles of gas and it needs to have an easy to read miniscus, so i can measure the gas correctly. I have tried water, but it can easily shift into vapour phase at room temp, iíve tried parrafin oil, but it is too viscous, as it traps little bubbles of gas. Iím not really sure what to use, because iím not a chemist. Iíd appreciate your suggestions as to what the best liquid would be. Thanks, Sean.
- Sean McConnell (age 22)
Brisbane, QLD, Australia
A:

  You might want to try Googling "low-viscosity vacuum pump oil" and see what turns up.  Oils come in a great variety of viscosities, and one might be suitable for you.  Itís not just viscosity which determines whether bubbles get trapped, although bubbles will get stuck in a really gummy fluid (like shampoo).  One common fluid in vacuum applications is mercury.  It has a high surface tension and does not wet glass, but it is usually very easy to read in gauges and has a low volatility at room temperature.  Mercury (including the vapor) is poisonous, however.

  Tom

(published on 10/22/2007)

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