If the refractive index of water under a certain temperature, say 20 degreeC, is 1.33334. Will it return to exact the same value after one or several heating and cooling cycles? Or will it shift a little bit to some certain direction (higher or lower than 1.33334)?

  • $\begingroup$ Depends on how pure the water is, perhaps. If you heat it for long enough in an open container, then the final value will end up much closer to 1... $\endgroup$ – Jon Custer Jun 28 '19 at 16:56
  • $\begingroup$ Sorry @JonCuster, I cannot catch your idea. Do you mean all the liquid water are vaporized? So, if the water are not completely vaporized. I simply heat 1 L water from 20 degreeC (refractive index = 1.33334) to 90 degreeC, and then cool down to 20 degreeC for several cycles. Will the refractive index perfectly go back to 1.33334 every time when the temperature is 20 degreeC? Thanks! $\endgroup$ – Fengfeng Jun 28 '19 at 17:02
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    $\begingroup$ If you have pure liquid water, a thermodynamically stable phase, why do you suppose that any path through phase space, returning to the same point, will affect the material properties? $\endgroup$ – Jon Custer Jun 28 '19 at 17:05
  • $\begingroup$ That's because I performed the heating and cooling cycle and finally obtained the relationship between temperature and refractive index. I detected large amount of refractive index change after one cycle but sometimes not. I wonder if this change is caused by the environment, the sensor, or water itself. @JonCuster $\endgroup$ – Fengfeng Jun 28 '19 at 17:12
  • $\begingroup$ fengfeng, can you really measure the refractive index of water to 5-decimal accuracy? what is the repeatability of your measurement tool? How many measurements did you take for each data point? $\endgroup$ – niels nielsen Jun 28 '19 at 18:34

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