Humidity Control: DIY Salt Packs

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pedant
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Sun Nov 01, 2020 1:52 am

lately, my favorite salt pack container is the 4 fl oz (120 mL) mason jar:

Salt Pack: tiny 120mL jar
Salt Pack: tiny 120mL jar
salt-pack-120mL-jar.jpg (71.78 KiB) Viewed 1768 times

they can be obtained from amazon for about 1 usd each. i bough a box of 40 of them, and it came out to 0.80 usd/ea.

also, i'm out of puerh storage space. oh no!
i had to get creative and use an old pressure cooker for this tong:

Pressure Cooker Storage (open)
Pressure Cooker Storage (open)
pressure-cooker-puerh-storage-1.jpg (72.9 KiB) Viewed 1768 times
Pressure Cooker Storage (closed)
Pressure Cooker Storage (closed)
pressure-cooker-puerh-storage-2.jpg (117.98 KiB) Viewed 1768 times
m2193
Posts: 20
Joined: Sat Jan 23, 2021 10:31 pm
Location: East Coast, USA

Sat Apr 03, 2021 4:22 pm

Does any part of the ratio have to be adjusted if I use iodized table salt instead? My school has salt packs that are iodized salt, and the ingredients list salt, sodium silicoaluminate, calcium sulfate, detrose, and potassium iodide. I would assume the additions are minimally concentrated though.
AndieB
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Joined: Sun Apr 25, 2021 12:00 pm
Location: Monterey, CA

Sun Apr 25, 2021 12:07 pm

I am testing my salt pack made as described in a gallon size Ziploc bag with the hygrometer, but for the last 12 hours it is between 80-85%. My temperature averaged 70F. Is it possible I'm having a pressure difference at sea level in California? Just wondering why my reading is so off from 70%...
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pedant
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Sun Apr 25, 2021 5:59 pm

m2193 wrote:
Sat Apr 03, 2021 4:22 pm
Does any part of the ratio have to be adjusted if I use iodized table salt instead? My school has salt packs that are iodized salt, and the ingredients list salt, sodium silicoaluminate, calcium sulfate, detrose, and potassium iodide. I would assume the additions are minimally concentrated though.
it shouldn't matter, but i prefer to use pure NaCl since it's already cheap. pickling salt that comes in a plastic bag is my current recommendation. it seems to be less smelly than the stuff that comes in cardboard containers.
AndieB wrote:
Sun Apr 25, 2021 12:07 pm
I am testing my salt pack made as described in a gallon size Ziploc bag with the hygrometer, but for the last 12 hours it is between 80-85%. My temperature averaged 70F. Is it possible I'm having a pressure difference at sea level in California? Just wondering why my reading is so off from 70%...
have you calibrated your hygrometer?
AndieB
Posts: 5
Joined: Sun Apr 25, 2021 12:00 pm
Location: Monterey, CA

Sat May 01, 2021 3:03 pm

pedant wrote:
Sun Apr 25, 2021 5:59 pm
have you calibrated your hygrometer?
For the brand new Govee hygrometers I'm using, their website says this:
"The device has been calibrated by precision instrument already. Normally it does not need to be calibrated again."

However, I am doing a calibration test with all 3 new hygrometers with a teaspoon of moistened salt in a gallon size ziploc. After 6 ours if each one does not read 75, I will adjust them. Thanks for pointing me in the right direction. My first experiment using hygrometers :geek:
Last edited by AndieB on Sat May 01, 2021 3:42 pm, edited 1 time in total.
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pedant
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Sat May 01, 2021 3:37 pm

AndieB wrote:
Sat May 01, 2021 3:03 pm
pedant wrote:
Sun Apr 25, 2021 5:59 pm
have you calibrated your hygrometer?
For the brand new Govee I'm using, their website says this about the hygrometer:
"The device has been calibrated by precision instrument already. Normally it does not need to be calibrated again."
even so, in my mind, the most plausible explanation is your hygrometer is out of cal.
therefore, i suggest calibrating it.

NaCl alone (without sucrose) gives ~75% RH:



see also:

viewtopic.php?p=25906#p25906
viewtopic.php?p=25992#p25992
AndieB
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Location: Monterey, CA

Wed May 05, 2021 8:34 pm

So I have calibrated all the hygrometers to 75% with just salt and water drops. I am now testing in separate ziplock bags: 100g distilled water and 70g NaCl pure salt (added last) with:

1. 17.5g sugar - 71.5% RH
2. 20g sugar - 85.5% RH
3. 22g sugar - 79.4% RH

I tested both my milligram and gram scales with a 50g weight, both are spot on. These are results after 1 hour. How long would you wait for equilibrium to be reached inside the ziploc? Also, seems like the RH should go down with more sugar. How are you heating the 100g distilled water to 65°C (150°F), microwave or on the stove in a water bath? Any thoughts on what I'm doing wrong? Should I be testing this in a Ziploc? I'm trying to get a reliable formula for a consistent 62% RH...
Thanks!
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pedant
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Thu May 06, 2021 8:58 pm

good questions, AndieB.
AndieB wrote:
Wed May 05, 2021 8:34 pm
How long would you wait for equilibrium to be reached inside the ziploc?
it depends on your setup. when i was coming up with what i wanted (~70% RH formula), i actually made an apparatus with a small fan inside to speed up the experiments.

i've done ziplock bag tests before too, and i just let them sit overnight because i wasn't in a rush. that is long enough ime. less time is probably also ok, but you'd have to determine that experimentally for your setup.
AndieB wrote:
Wed May 05, 2021 8:34 pm
Also, seems like the RH should go down with more sugar.
...
Any thoughts on what I'm doing wrong? Should I be testing this in a Ziploc?
yes, sugar should depress the humidity at equilibrium.

if you believe the theory, then something is "wrong" with your procedure to give you that data.
your measurements of >75% RH in particular are peculiar. did it not cool down to room temp yet? were there stray drops of water on something? those are the kinds of things i'd guess could have happened. also, is your ambient RH crazy high?

a ziploc should be fine if it is of good quality and in good condition. i have used them and gotten results consistent with other test chambers (sealed jars, vacuum desiccation chambers, etc.).
AndieB wrote:
Wed May 05, 2021 8:34 pm
How are you heating the 100g distilled water to 65°C (150°F)
for convenience, i used an electric kettle. i think i had de-scaled it recently, but honestly i don't think a small amount of mineral solute (i.e. many waters you'd consider drinking) would affect the results. i just suggest using distilled water to make it more of a standardized procedure. i don't want people to use pond water and unrefined sea salt.
AndieB wrote:
Wed May 05, 2021 8:34 pm
I'm trying to get a reliable formula for a consistent 62% RH...
why 62%? believe it or not, some people just use plain salt without sugar in their pumidors. even though this normally gives 75% in a sealed chamber, if you have a lot of tea in there, you open it somewhat regularly, and you don't have a bunch of salt packs (i.e. the salt pack is a bit undersized for the application), the RH never gets dangerously high anyways. i don't recommend that for everyone, but it works for some people.
AndieB
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Sat May 15, 2021 11:07 am

pedant wrote:
Thu May 06, 2021 8:58 pm

why 62%?
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