Hydrometer Calibration Question

[SSDVC]

I read the thread about hydrometer calibrating and I have a question. How and why does the environment inside the plastic bag reach and maintain 70% humidity? Why not 65 or 75%. Wouldn't the size of the cap and amount of salt or water in the cap make a difference? A lot of variables for a steady 70%.

Hey, I'm a cigar smoker, not a rocket scientist!

[shilala]

It's a physical property of salts. Many salts yield a specific RH over themselves when saturated.
When you put the salt in a small area and make a solution of it, it will release water from itself and gather water into itself, all the while trying to be about 75% RH.
Different salts yield different RH's.

[kenstogie]

http://sites.google.com/site/kenstogie2/salttest.
all you could ever want to know about the salt test.

[shilala]

Originally Posted by kenstogie

http://sites.google.com/site/kenstogie2/salttest.
all you could ever want to know about the salt test.

Awesome info page, Ken. Thank You!!!
There's a real good salt missing from your list. It's Sodium Nitrate.
Sodium Nitrate yields a 66% RH over the solution, which is a lot closer to where we want to be.
The tie in there is that whenever we calibrate any type of instrument, we want to calibrate it as close to the range where we work.
If a guy is keeping his cigars around 70%RH, Sodium Chloride (table salt) is great. If it's iodized, they generally use Potassium Iodide and it'll change the salt's range down closer to 72%. (I did the tests and although the numbers were all over for iodized salt, that's a good average.)
Sodium Nitrate is a meat preservative, it's readily available, and it yields a 66% RH. It's best to hunt up scientific grade (pure) stuff at ebay. It's super cheap.
The cincher for calibrating as close to our intended range is that if a hygrometer is off by 6 points at 75%, it doesn't at all mean it will be equally screwed up at 65%. It can be off far more, or much closer to actual.
That point is especially true with those white Walmart hygrometers you see around. I had a couple that were 12 and 14 points off at 75%, but were only 4 and 6 points off at 66%. Sounds weird, but that's how it is.
The reason for that is that Temperature and Relative Humidity is not mathematically congruent, that is, there's no true relationship numberwise like there is with temperature and pressure.
They're only loosely jived.


****Disclaimer****
Mind ya, this is just for the super-anal. It's a sickness with me, but it comes from years of using measuring instruments at work and having to calibrate all the time. It's not at all necessary to be so anal.
If a guy's hygrometer is off a couple points, it really doesn't mean squat.
It's best to listen to what the cigars are telling us. 70% makes wet cigars and crooked burn issues, but it also makes for fuller flavors.
Down at around 62%, my cigars burn razor sharp and there's no plugging or cracking. It's a good tradeoff for me and I end up throwing less cigars in the alley.
I calibrate my hygrometers far less frequently now, and look at them even less frequently. So long as they are smoking good and feel and smell right, I'm happy.

[SSDVC]

Fantastic info...........Thanks!