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You could do it empirically like this:put a volume of gas in a graduated cylinder and record volume.wait some period of time and record timemeasure volume left in cylinder.calculate rate of evap by (initial volume - final volume / time in min)surface area would be an important factor too. so you could calculate the cross sectional surface area in cm^{2} of the cylinder (pi*r^{2}) and then divide the rate by that to give units that show change in volume per time per surface area (ml evaporated/min)/cm^{2}.this would not be generalizable to all situations but it would give you an idea of what goes on at atmospheric conditions.

That is true Jim. The cylinder is not applicable to all conditions. Fill the cylinder all the way up, or most of the way, and measure for a short time. Then it should not matter. About weighing gas, how can one back calculate to a volume by weighing a volatile liquid of unknown density with any kind of accuracy? I am not nit picking, I'm just trying to understand how that would work. I don't think of gasoline in terms of weight but in volume so that confuses me.

Quote from: NOLAGuzzi on February 22, 2011, 03:31:54 PMThat is true Jim. The cylinder is not applicable to all conditions. Fill the cylinder all the way up, or most of the way, and measure for a short time. Then it should not matter. About weighing gas, how can one back calculate to a volume by weighing a volatile liquid of unknown density with any kind of accuracy? I am not nit picking, I'm just trying to understand how that would work. I don't think of gasoline in terms of weight but in volume so that confuses me. Measure it first in a closed container.