I see no reason to make fuming nitric acid, it is not needed in refining.
In fact I will not discuss fuming nitric here on the forum, or give anyone advise on how to make it, or help them make it, for it has no use in refining at all, and many times those trying to make it can easily do harm to themselves or others.
Personally I would never leave a distilling rig unattended, that is a disaster just waiting to happen.
You can make and distill a 70% nitric acid much easier than you can the more concentrated acid.
You can make a weak nitric acid and easily concentrate it to the azeotropic 70% nitric acid.
For some processes weaker nitric acid is actually needed and can easily be made at this lower concentration.
The boiling point of the acid depends on concentration, and when distilling (or evaporation) this concentration changes during the process (and so does the boiling points).
Since you used an all glass rig (no metal) I still cannot understand where the solution would turn green, I can see where you could have decomposed the nitric with high temperature, but then I would expect it to look yellow or orange to dark orange/red with NOx gases, I have never seen it green.
Although nitric can decompose forming many different NOx gases (so I guess it is possible one of these may have given your solution the color you experienced), if you did not have any metals, tubing, corks or other materials to give this color to the solution.
(Actually you can tell an acids concentration by its boiling point, if you have an accurate way to measure the boiling point), density or titration is just an easier methods to tell an acids concentration.
Water boils at 100 degrees C (212 deg. f),
Nitric acid boils at different temperatures depending on its concentration.
With nitric acid, as the acid concentration rises, so does the boiling point of the acid, until the azeotrope nitric acid solution is reached.
O% HNO3 has a boiling point of 100 deg C (water)
20% HNO3 has a Boiling point of 103 deg. C
30% HNO3 has a Boiling point of 107 deg. C
50% HNO3 has a boiling point of 116 deg. C
70% HNO3 has a boiling point of 121 deg. C
(note here were boiling point is lower for the more concentrated acid).
90% HNO3 has a boiling point of 102 deg. C
98% HNO3 has a boiling point of 86 deg. C
(actually below the boiling point of water).
You do not need to boil an acid to concentrate it vapors will leave the solution below the boiling point of the liquid.
With evaporation water can be removed from a dilute solution of nitric acid, concentrating the acid, until the azeotropic solution of 70% HNO3 is reached, further evaporation will just vapor of 70% HNO3 until the vessel is dry. you cannot concentrate the acid further by this process, so it is possible to concentrate a solution of 20% HNO3 up to 70% HNO3 by carefully vaporizing off the water from the acid. Note with this process the boiling point of the acid is helpful to know, but we do not need to boil the solution (actually boiling would be counter productive), we can do this keeping the acid below the boiling point of the acid at that concentration, and still vapor off liquid easily.
Evaporation and boiling are distinctly different, evaporation liquid is vaporized off the surface. Boiling is the bubbles of gases forming from the bottom of the solution rising to the surface and releasing these gases in small explosions of the bursting bubbles.
The pressure of the atmosphere above the liquid can change the boiling point of liquids.
Example water can be boiled at room temperature under a vacuum, and in a pressurized vessel water will not boil even at 100 deg C (or 212 deg. F).
Example at O PSIG (14.7 PSIA) water boils at 212 deg.F (100deg. C)
Or
At 30 PSIG water boils at 374 deg. F.
In a vacuum at 29"HG water boils at 40 deg. F.
When heating a solution or mixture of liquids, the different liquids in solution have different vapor pressures, and boil at different temperatures, the more volatile mixture will be the first to leave the solution.
When the solution or mixture of different liquids have different enough boiling points they can often be separated into individual components by distillation (or evaporation).
When the solution is heated the temperature of the solution will rise when heated until the solution reaches the boiling point of that liquid (or the most volatile liquid), adding more heat will not raise the temperature of the liquid any further until all of that liquid has boiled off, then the temperature of the solution will rise again until reaching the boiling point of the second liquid in solution the added heat again will not raise the temperature of the solution until this liquid has been boiled off.
Sulfuric acid also has different boiling points depending on its concentration.
At 450 degrees F, that is the about the boiling point of 85% H2SO4.
The approximate boiling point for 35% H2SO4 is about 225 deg. F.
65% H2SO4 boils at about 300 deg. F.
98% H2SO4 has a boiling point around 620 deg. F.
