Salt test...is it possible to screw it up?

[Scott M]

Did a salt test on one of my digital hygrometers yesterday. Getting readings like 67%. Wet salt, but not enough to turn it into sloution. Just wet, like beach sand.

I plan on retesting later this week, but is it possible to perform this incorrectly, and what happens?

(I outta be able to figure this out, but P-chem was about 8 years ago!)

Thanks!

Scott"madpsuedoscientist"M

 

[SeanGAR]

Salt solution has to be saturated,

You need to reach equilibrium in the headspace water vapor pressure.

Other than that should be hard to mess up.

Two of my digitals (little havanas) read 78 in saturated NaCl not 75 as expected, but my Radio Shack was dead on.

Sean

 

[Roger Miller"]

There are only a few requirements.

Sealed environment: this should go without saying, but make sure there is no exchange with external environment. Double bag is not unreasonable.

Adequate air "circulation" within the test environment. I have heard where sometimes the salt solution is in a cup in a plastic bag and the bag covers the cup and the hygrometer is outside. This can create two environments with different RH. Be sure there is adequate room for air exchange throughout your chamber. Also be sure that the sensing ports on your hygrometer are not obstructed.

Salt/water solution: sounds like you have this part. What you are looking for is two things; first the salt must not be disolved only wetted, second; there has to be enough water to raise the RH in the environment you have created. (this assumes an ambient RH below 75%) It should have the texture of a paste, but you should still be able to see individual salt grains.

Time: patience is a virtue. Depending on the size of your experimental chamber this can take quite a bit longer than you may expect. Let it sit over night.

Temperature: anywhere near room temperature (70 degrees F +/- 10 degrees) is fine. Just don't be doing this on your back porch in the winter in Up State NY.

Also, be sure to place your hygrometer where you can read it without opening your test environment.

That's it really. I would not be too surprized if your hygrometer was off 2 to 6%, but 10% is a bit high. Oh, you are using Kosher salt right? :r j/k

_____
rm

 

[1f1fan]

Good advise from Roger Miller, but.....If the salt test does not work for you get a Boveda Humidity Packet. The humidipack is what Feunte and Torano are putting in their boxes now to keep them fresh.

Follow the directions on step 5 from the Cigar Solutions site. This is the most accurate way to test a hygrometer now. The humidipaks are supposed to be accurate within 2%.

I may get a few of these for my smaller desktop and for the travel humis.

Good luck, hope this helps.

 

[SeanGAR]

What you are looking for is two things; first the salt must not be disolved only wetted, second; there has to be enough water to raise the RH in the environment you have created. (this assumes an ambient RH below 75%) It should have the texture of a paste, but you should still be able to see individual salt grains.

Nice post Roger.

I would just add that the salt solution only has to be saturated, which can look like mostly water with undissolved salt on the bottom, it doesn't have to look pasty. I boil water and dissolve salt as much salt as possible, then cool it down and the lower solubility at lower temp will result in a bit of precipitation. That is for sure saturated and with enough water to speed the equilibrium development.

Your point about adequate water is excellent and important, I think people putting pop caps of salt paste in a big tupper will have to wait days for equilibrium. I will also note that the saturated salt solution will remove moisture from the atmosphere if the ambient RH is above 75%.

Follow the directions on step 5 from the Cigar Solutions site. This is the most accurate way to test a hygrometer now. The humidipaks are supposed to be accurate within 2%.

Saturated NaCl will be more accurate than 2% over a wide range of temperatures. We use this and other saturated salt solutions for experiments with water activity and food quality. The nice thing besides availability and cost for NaCl is that its RH is largely unaffected by temp over a very wide range: 5-40C. The exact RH is generally reported as 75.1-75.2% using extremely accurate water activity detection devices costing thousands. In lab last week, my students reported average values of 75.14.

Sean

 

[Uniputt]

I can't really add too much to the dxcellent information above, other thatn telling you my own experience.

I used a restaurant "bullet" (a small bowl-type container that they use to serve a condiment in--like hot sauce) and put about two teaspoons of salt in it. Then added distilled water to form a paste. I placed it in a tupperware bowl. Dropped in the digital hygrometer face-down (so I could read it through the bottom), and burped out the air to form good seal.
I let it sit overnight, and wa-la. I was most pleased that my Western Scientific hygrometer read 75% the next morning. (hooray!)

Then I repeated it again to be sure. Same thing. I did notice that there was water floating on top of the salt paste. If you stirred it up, it would disappear for a while, then form back. Maybe you just didn't have enough water in your salt container. (Does it matter if it's distilled or not? I don't think it does, for the sake of this test, however, since I had it lying around anyway.....)

I then threw in the cheap analog hygrometer I had. I thought I had properly calibrated it by wrapping it in a wet paper towel...to get a 98% reading (when I got my first humidor....those were the instructions in the box....boy, was it wrong!....Newbie ignorance can be bliss!!) The analog was reading way, way off. So I corrected it, after letting it sit overnight. Then I promptly gave it away to my friend who's been using it ever since. No problems.

Hope this helps.

 

[pinokio]

Suppose I must get myself a digital hygrometer. I salt tested my analog and the reading was 84%, meaning that at the moment I have it at 78-80% to compensate the 9% error.

Regards

 

[RonC]

In an airtight canister, the Humidipaks will be accurate to within a half %. Salt test is accurate too, just a little less room for a mistake with the Humidipak.