Day 1 Results:
24 hours have elapsed since the start of the test, and some slightly unanticipated results have emerged, though it's too early to tell if they will hold throughout the course of testing.
From the open-air test, I know that in a normal environment where the sugar solution is exposed to air without constraint, the evaporation curve is perfectly linear until the sugar solution has reduced to a certain point. In other words, water evaporates from the sugar solution at a consistent, unchanging rate. I would expect the same to hold true in the liquid feeders, except that doesn't appear to be the case.
Take a look at the difference between "12 Hours" and "1 Day" for both Mini Liquid Feeders. Given that both measurements were 12 hours apart, the expectation would be that "1 Day" Brix value would be double the "12 Hours" value, but it is less in both Mini Feeder tests.
One observational note is that after just 24 hours, when feeders containing a sugar solution are inverted, wavy distortion emanates from the base of the feeder down through the liquid. I'll try to take a photo of this at some point, though it may be impossible.
This refractive phenomena is caused by a difference in density of the solution between the top and bottom of the glass vial which holds the liquid. The liquid at the bottom of the vial has become significantly more dense than the liquid at the top. This may be because all the air exposure occurs at the bottom, and without any form of agitation (unless ants are drinking the liquid, producing air bubbles to displace the consumed liquid), then the liquid at the bottom of the feeder will contain a higher sugar content compared to the vial contents as a whole.
As the liquid reduces into a syrup, it reaches a critical point where the concentration is so high, that reduction slows because the attractive force of the sugar to water is greater than the force needed to cause the water to change from a liquid to gaseous state. One future test that is needed will be to determine the difference in density of the sugar solution between the top and bottom of the glass vial. The vial would need to be inverted in such a way so as to minimize the amount of agitation, so that little mixing occurs. Then, a pipette could retrieve samples from various positions in the vial.
All this is to say that a good rule of thumb may be that for all sugar solutions, it is probably best to agitate them in the liquid feeder by inverting the feeder every couple days. This way, the liquid at the base of the feeder remains at the optimal concentration and freshness.
Edited by drtrmiller, May 21 2019 - 4:15 AM.