When we heat water, we see bubbles appear as the boiling point approaches. The water then "boils" vigorously as it is converted from the liquid phase to a gas.

I realised recently that during an ether extraction of a product, a lot of ether had evaporated, as was evident from the mass balance. The ether vapours were visible, but no "boiling", or fluid motion that we tend to associate with boiling, was observed. The boiling point of ether is $34.6\ \mathrm{^\circ C}$. The ambient temperature then was around $35\ \mathrm{^\circ C}$.

Question: Why do we not see ether "boiling" near its boiling point?

Let me also put forth my thought process: The most apparent difference between the two cases of boiling water and boiling/evaporating ether is the location of the heat source. The ether was kept in a beaker on a stable platform, so it could exchange heat through the upper surface and the walls of the beaker. Heating water from below might create pockets of 'hotter' and hence less dense water that might lead to the "boiling". In the case of ether, the only possible explanation I found believable was that the walls of the beaker were really bad conductors of heat, as we would have seen some fluid flow in the ether case as well.

We also see puddles of water evaporating off. In that case, the heat exchange is possible only from above. Considering no disturbances, there is no visible fluid motion in the puddle. I felt this was because the rate of evaporation was too low. In the case of ether, it is already at its boiling point. This leads me to believe that in a restricted environment as a beaker, when the ether changes phase, the vapour accumulates near the surface as it is denser than air (almost 2.5 times as much). This further slows down the transfer of heat. Taking this into account, I find it very hard to believe that about 5 g of ether was lost in a mere span of a bit less than 10 minutes.

Is my reasoning right, or is it flawed? Please do tell.

Notes & References:

  1. Diethyl Ether - Wikipedia
  2. weather.com and personal experience
  3. Modified Ideal Gas Law: $\rho=\frac{pM}{RT}$, i.e. $\rho\propto M$, taking $M_\text{air}\approx 28.84\ \mathrm{\frac{g}{mol}}$
  • 4
    $\begingroup$ I believe the ether was slightly cooler than its surroundings (mostly due to evaporation), and thus below its boiling point. $\endgroup$ May 18, 2017 at 11:55
  • 1
    $\begingroup$ You can see ether boil if you heat it slightly more strongly - DO NOT do that without supervision, though. $\endgroup$ May 18, 2017 at 11:58
  • $\begingroup$ This was an EXTREMELY dangerous experiment, if you actually performed it at an outside temperature of 35°C. You break an ether bottle at that temperature, and huge amounts of it will have evaporated when, almost inevitably, the fumes have found an ignition source. In a cool lab, you get scorched a bit, OK. In yours, you´re toast. No fume hood window will save you. $\endgroup$
    – Karl
    Dec 23, 2019 at 18:33

1 Answer 1


The issue here, as eluded to in your discussion, is that near the boiling point the rate of heat being removed from the ether (via rapid evaporation) was greater than the rate of heat being transferred into the ether, so that the temperature of the ether never reached it's boiling point. In fact, the ether was likely several degrees below it's boiling point due to the evaporative cooling.

The rate of heat transfer into the solution via conduction from the surrounding air is a function of the difference in temperature between the ether and the air, which in this case was very small. If the ether had been placed in an oven of a sufficient temperature, the ether would have boiled.

The mass loss that was observed is not at all unexpected, as the temperature of the ether was just below it's boiling point. Imagine how quickly water would evaporate from a beaker if the surrounding air temperature was $\pu{99^oC}$ (and assuming we're at sea level so the water doesn't boil). The vapor pressure of water, and ether, is only slightly less at a few degrees below it's boiling point than it is right at it's boiling point. (Of course the physical action of boiling also allows for more rapid evaporation, so long as sufficient heat is applied to keep up with the evaporative cooling).

Summary, TL;DR:
As the ether was close to it's boiling point, it was evaporating rapidly, resulting in rapid mass loss. The evaporative cooling near the boiling point happens at a rate to greater than the conductive heat transfer from the surrounding air, so that it never quite reaches it's boiling point, and actually cools to several degrees below it's boiling point.


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