# flash point vs. boiling point

Discussion in 'Off Topic' started by IceBergSLiM, Oct 3, 2008.

1. ### IceBergSLiM Lifer

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say i have 80 proof 40% alc/vol rum

how do i determine flash point and boiling point?

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2. ### Fenixgoon Lifer

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the boiling point is when the vapor pressure of the liquid is equal to the atmospheric pressure. if i were really ambitious, i'd look it up in a thermo book, because generally it goes something like:

ln(P) = A*T + B*ln(T) + C/T^2. you also have to account for the fact that you have a mixture (but it has complete solubility). so we'd use raoult's law and the other one, which i can't remember off the top of my head, heh.

oh thermo, it's only been a year, but i've forgotten it all already :brokenheart:

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3. ### IceBergSLiM Lifer

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how do i figure that out for an 80 proof rum?

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4. ### IceBergSLiM Lifer

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yeah that might as well be chinese for mje what are p, a, t, b, mean?

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5. ### gorcorps aka Brandon

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80 proof rum means 40% by volume alcohol, which is ethanol. The other 60% is assumed to be water. Ethanol has a BP of 78.4°C and water at 100°C. You can use those temps and fractions to estimate the boiling point (with the assumption your atmospheric pressure is 1atm or 760mmHg(torr)).

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6. ### IceBergSLiM Lifer

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flashpoint anyone?

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7. ### Paperdoc Golden Member

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You could try requesting an MSDS Data Sheet from a distiller. Those are the sheets that specify a whole bunch of safety-realted info, required in all industrial workplaces to ensure workers are aware of all hazards and safety precutions. They will ALWAYS specify the Flash Point if there is one, and many contain the boiling point also.

I don't know if 80-proof alcohol has a Flash Point. That is the temperature for a liquid at which it will spontaneously burst into flame without exposure to a direct ignition source. While the rum may burn when lit with a match, that is not the same thing.

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8. ### Brainonska511 Lifer

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Even then, you don't need to estimate the boiling point, as the ethanol will hit the BP of 78.4C and start boiling off at that constant temperature. After the ethanol boils off, the temperature will continue to rise until it hits the boiling point of water. This is the general idea behind distillation (boiling and recondensing so that the alcohol ends up in greater and greater concentrations).

As far as flashpoint, isn't that the temperature at which it will combust?

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10. ### Tiamat Lifer

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Um, flash point is completely unrelated to boiling point. Flash point is the minimum temperature required for the it to become ignitable in air.

If you want to flash your rum, its not going to be very easy since its ethanol content is low. Pure ethanol flashes at 12.8 celcius. Flash point of 54% rum is about 22 celcius. Normal rum will be higher while Bacardi 151 will be in between 13C and 22C as you can see this trend...

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11. ### Itchrelief Golden Member

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I'm talking out of my arse here, but I would suppose it would have some relationship with the volatility of the flammable substance, since it is usually the vapors that combust.

By wildly making assumptions, I would think you'd probably need to know the minimum % of alcohol vapors in air to sustain combustion, then find at what temperature you will get a partial pressure of alcohol that corresponds to that %.

Assuming the above is true, lower boiling point means more vapors = lower flash point, assuming the combustion occurs at the same % of vapors in air.

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12. ### Tiamat Lifer

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see my edits.

Alcohol won't behave linearly, however, a rough guess can be had with linear interpolation.

Problem with flash point is the second you remove the ignition source, the flame goes away. If you want the flame to remain you have to reach the Fire Point, which is somewhat higher.

For this reason, Bacardi 151 is relatively easy to keep on fire at room temperature conditions (while normal Bacardi rum is not as easy).

If you want a more exact Flash and boiling point, you will need a chemistry lab and learn rudimentary thermodynamics through wikipedia.

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13. ### olds Elite Member

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MSDS?
EDIT
Guess they don't have them for "food".

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14. ### IceBergSLiM Lifer

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f that shit. lol

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15. ### Tiamat Lifer

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If you have some extra rum why dont you just try the experiment?

All you need is a thermometer, and a heat source.

1. Put rum in cup with thermometer.
2. Keep fire extinguisher very close by
3. Test rum at room temperature with a lighter. Did it light? (Yes/No). If not, increase temperature.

4. Record the temperature that the rum flashed.
5. Record the temperature that the rum started boiling.

6. What did you learn from this experiment?

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16. ### Eli Super Moderator<br>Elite Member Super Moderator

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The boiling point of ethanol, as someone mentioned, is 173.1ºF.

The flash point of 40% ethanol/60% water is 78.8ºF.

That's probably close enough for your rum.

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17. ### Tiamat Lifer

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Seems reasonable compared to linear extrapolation from the data I supplied earlier.

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18. ### IceBergSLiM Lifer

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so buy your calculation if I'm drinking rum on a hot summer day its going to explode?

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19. ### DisgruntledVirus Lifer

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With an ignition source it could ignite and burn, but not explode. The flash point is not the temp where a vapor will explode, but instead where it will ignite. It may or may not continue burning when the ignition source is removed.

per wiki

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20. ### IceBergSLiM Lifer

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sorry guess I'm confusing flash point with auto ignition point

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21. ### RapidSnail Diamond Member

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No. The liquid must be 78.8ºF for it to be ignitable. How many people drink bear at ~80 degrees on a hot summer day?

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22. ### DisgruntledVirus Lifer

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I want to know how many people drink bear

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23. ### alkemyst No Lifer

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guess it's the same with push and pull with you.

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24. ### RapidSnail Diamond Member

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Oops. I should have said "bare." Which might make sense! :laugh:

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