PirateDocBrown - 31-12-2016 at 15:01
So, I'm walking through the local Asian supermarket, and see some plastic bags labeled "alum" on the shelf. Nice, clear big crystals inside, it's
gotta be pretty pure! And at 79 cents for a half pound, how can I go wrong?
So I take it home, and get a closer look at it. A smaller crystal goes into the mortar, and made into fine powder, mixed with a bit of NaOH, and into
a test tube with water.
Distinct smell of ammonia! Not strong, but it's there!
Fire up the butane torch, and more powder onto a wet wire, then into the flame. Yellow flame, could be sodium contamination, but no visible purple.
I gotta get a cobalt glass plate...
So, is ammonia alum commonly used for food ingredients? I'm accustomed to seeing the potassium salt.
Morgan - 31-12-2016 at 15:29
Here's this
https://lotusalum.en.alibaba.com/product/1779715957-22152271...
http://shanghaiist.com/2016/05/11/fake_jellyfish.php
[Edited on 31-12-2016 by Morgan]
brubei - 31-12-2016 at 15:46
Aluminium sulfate crystal is commonly sold as natural antiperspirant
[Edited on 31-12-2016 by brubei]
Sulaiman - 1-1-2017 at 10:51
alum commonly means potassium aluminium sulfate
but any double sulfate salt with a monovalent and trivalent metal salts, e.g. https://en.wikipedia.org/wiki/Mendozite
which could explain sodium instead of potassium
PirateDocBrown - 1-1-2017 at 15:03
Alum sold for human consumption is indeed supposed to be potassium-aluminum. Ammonium-aluminum, while not toxic, is usually used for industrial
applications.
My nose most definitely detected ammonia. I'm wondering how common this is in Thai alum. I'm further wondering exactly what this alum was sold for?
Making pickles? Deodorant? Shaving?
Small amounts of sodium can easily throw off flame tests, which is what I think had happened here, though cobalt blue glass lets you detect potassium
flame, despite sodium contamination. Pure sodium-aluminum alum makes poor crystals, as it is highly deliquescent.
BromicAcid - 1-1-2017 at 18:38
Most interesting thing that I have seen at the Asian supermarket is 18% acetic acid.
Amos - 1-1-2017 at 19:28
I always see some alum or another, sometimes the classic potassium aluminium sulfate, sometimes ammonium or sodium, as additives in cup noodle and
ramen. That and it's historically been applied to the skin as a deodorant of sorts.