Science related Humidity Question.

[Rescon]

Bought some potassium carbonate powder from Amazon and proceeded to do a “salt”test for calibration of my to 2 analog dial hygrometers. Used a small glass ramekin with maybe 2-3grams of salt. Read it would exotherm so cant use plastic. Got the slurry consistency needed but within minutes, the mixture became harder and harder as it released heat. I let it sit for about 5 minutes, became hard as a rock. Can’t find any info on what this means or that to do different
Any ideas??

~ Nick

[619TF]

Instead of "potassium carbonate powder" just use actual (table) salt (sodium carbonate) which will neither exotherm nor harden.

[Rev Roy]

I just use these. I like easy.

[Rescon]

I used the Boveda 32% packets and they were so far off from both of my Hygrometers that I don’t trust it.
Table salt is for a much higher point of reference 75%. I may try this just to see but the a long way away from 40-45%

[Rescon]

I am very familiar with exothermic reactions as I work with Epoxies and other chemical that have this characteristic. Maybe it’s just too much salt. Sometimes the shear volume of the chemical can lead to a very quick and hot reaction feeding the fire so to speak.
Hard to find specifics about this but based on pics I saw online, it was less than I saw being used for calibration.

[The Bard Rocks]

Originally Posted by 619TF

Instead of "potassium carbonate powder" just use actual (table) salt (sodium carbonate) which will neither exotherm nor harden.

NACl = sodium chloride --- do you mean that?

[619TF]

Originally Posted by The Bard Rocks

NACl = sodium chloride --- do you mean that?

Yup, that was a typo based upon the original posting which threw me as I didn't know about the other chemical discussed (potassium carbonate).

[Dbone]

Boveda themselves say that the most accurate level to calibrate at is 75%.

[Simon Fay]

Potasssium Carbonate is generating nowhere near enough heat to melt plastic in a salt solution calibration test !!!

I build guitars for a living and calibrate my hygrometers every year with this method. The salt you want to use is K2C03 since it's in the range we want to measure.

You want to make a slurry - no dampened salt -- a slurry. If anything, add more water. You just want to make sure that not all of the salt has dissolved in the solution. I always have a layer of water on the bottom of my calibration container. and as long as you see the salt as well, then you know the solution is saturated. I use a large Tupperware container and fill the bottom with my saturated salt solution. I have my hygrometer resting atop a small plastic mixing cup. I closer the lid and wait 24 hours for the environment inside the container to fully reach equilibrium and then check the measurement of the hygrometer. It should read 43%. And that's it - you're golden.

In terms of accuracy - it doesn't matter which salt you use -- you're only getting a 1 point calibration. Ideally, you would test at least two throughout the full range - that's how instruments are calibrated in a lab (ph meter, etc ... ). For our purposes, the Potassium Carbonate is the best salt to use and a 1 point calibration is just fine.

[DesertTwang]

Or, you could simply stop all this monkey business from Chemistry 202 lab class and get a hygrometer calibration kit that lasts for multiple calibrations for 8 bucks on Amazon...

Worked for me.

[Edgar Poe]

Originally Posted by 619TF

Instead of "potassium carbonate powder" just use actual (table) salt (sodium carbonate) which will neither exotherm nor harden.

The other day I was calibrating my hygrometer. I used plain salt, in a water bottle cap, I added water to the salt, placed them both in a baggy, after I checked the meter the next day. The salt in the cap was rock hard ?

Ed

[BradleyS]

I utilize a Sling Psychrometer and have been very happy with the results.

[619TF]

Originally Posted by Edgar Poe

The other day I was calibrating my hygrometer. I used plain salt, in a water bottle cap, I added water to the salt, placed them both in a baggy, after I checked the meter the next day. The salt in the cap was rock hard ?

Ed

Not enough salt. As stated before, you really need a slurry.

[Rescon]

OK, Well if anyone know what a slurry is, it should be me as I have been in the concrete repair business making slurries for 25 years. It was the consistency of a milkshake. but by no means did i have enough to fill the bottom of my tupperware container. Its about 1.8 gallon size
Hey Simon, about how much solution volume do you think you use?
Is the solution hard and dried up after 24 hours?

Also, just noticed that my powder says " product intended to be used in beer and wine making" No chemical formula of K2CO3 on bag. Not sure if there is something unique about this stuff.

Im going to use a much higher distilled water/salt ratio this time. Hopefully, i won't have to get the jackhammer out to clean up

Ill report back for all you "if science says its true than its true" people

Nick

[Simon Fay]

I use a small Tupperware container - I'd say it's about 4-6" length and width and maybe about 4" tall. I sprinkle the salt on the bottom and fill so that there's about a 1/4" of water on the bottom. As long as I see some salt undissolved in the solution, then I'm happy.

I use a very "wet" slurry - technically, a bit to wet to even call it that. Think iced tea that has sugar floating around in the bottom of the cup and that's what I'm aiming for. My solution would probably take a week or so to dry out if I left it uncovered. You want lots of liquid if possible as that will help speed things up in terms of your container reaching equilibrium.