----- Original Message ----- > You have failed to understand the example, and changed what I said. Sorry I > was not clearer that all factors *except* the number of molecules in the > container were the same. > > Regards, > Don Rose, B.Mus., A.M.U.S., A.MUS., R.P.T. I don't think I changed anything you stated, but rather asked for clarification, which is still needed to understand what it was you said. However...... If you have a container of air that has some moisture in it of let's say 50% RH, and remove some air from the container, I think the RH will remain unchanged at 50% (or there abouts - I don't know - does atmospheric pressure affect RH some small amount?). I guess the question is whether atmospheric pressure affects the saturation vapor pressure. RH is defined as: The ratio of the actual vapor pressure of the air to the saturation vapor pressure. So if you remove air (oxygen, nitrogen, etc. and water vapor) from a container, you lower the atmospheric pressure in the container, which would presumably lower the saturation vapor pressure, but by removing some water vapor, you would also lower the water vapor pressure - and I would think, proportionately the same amount. So, I'll admit that I'm not 100% sure, but I think RH would stay about the same, if not exactly the same. Maybe someone can weigh in on that - I thought we had a resident chemist? Now it is true that if you remove some air (and water vapor) from the container, the absolute humidity would be reduced, as absolute humidity is defined as: The ratio of the mass of water vapor to the volume occupied by a mixture of water vapor and dry air, or the mass of water contained in a unit volume of moist air. Terry Farrell Bob Davis wrote: Relative humidity is the amount of water vapor in the air, versus the amount it can hold, at a given temperature. If the temperature is, say, 70 degrees, and the air is holding all the moisture it possibly can, the RH is 100 percent. Since warm air holds more water than cold air, if the temperature then rises, the RH would go down, since the warmer air would be capable of holding more water. Ambient humidity is just the relative humidity at a particular location, like in the living room where the piano sits. Exactly, Bob. Don Rose, B.Mus., A.M.U.S., A.MUS., R.P.T. wrote: Suppose you have 1 liter of air and it is at 20 degrees Celsius. Suppose the measured humidity inside the container is 30%. Absolute humidity or relative humidity? If one increases the temperature without allowing any air to escape the humidity will remain at 30%. The absolute humidity would remain constant, but the relative humidity would decrease in the scenario above. If on the other hand one allows air to escape--then there are fewer molecules of air--and fewer molecules of water so the "relative" humidity will be lower. Impossible to predict without additional information. Are we still increasing the temperature? Are we allowing the environment in the one liter vessel to equilibrate with the surrounding atmosphere? Theoretically, if one opens the vessel, and if the humidity outside was 100%, then both absolute humidity and relative humidity could rise in the vessel. By itself, relative humidity has nothing to do with "letting air escape". Terry Farrell -------------- next part -------------- An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/20060327/f23e2a4a/attachment-0001.html
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