LiveWire - 9-3-2006 at 00:42
Last night I tried to concentrate some sulfuric acid (it started out as battery acid, at around 38%) by boiling it down.
The acid started out completely clear and colorless. As it got hotter, it started getting more and more yellow. At around 320 degrees Celsius, the
temperature stopped rising. At the same time, the acid turned murky! After about 10 minutes passed and the temperature didn't rise one bit, I turned
off the heat and let it cool.
The resulting acid isn't yellow anymore, but it's still got that white milky appearance, and there is some white stuff at the bottom of the balloon.
Can anyone explain to me what's going on?
Could it be because of the "boiling rocks" I used? I asked for boiling rocks and they gave me a bunch of tiny glass spheres.. That is correct, isn't
it?
Acid
MadHatter - 9-3-2006 at 03:36
If the acid came from a car battery, it could be lead sulphate. Did you take it from a battery
or obtain it as a battery refill ?
LiveWire - 9-3-2006 at 05:06
No, it was a refill.
Though since I got it from a small shop, perhaps there is a very small chance that they ripped me off and gave me "used" acid.. Is there any way I can
check for lead sulphate?
It just seems really odd to me, since it happened at exactly the same time that the temperature stopped rising. I thought perhaps it was a normal
thing like the color change, but then it didn't go back to normal!
12AX7 - 9-3-2006 at 05:13
Hum... take a sample of the precipitate, boil in baking soda solution, then test that the result (which ought to be mostly lead carbonate) is
insoluble in sulfuric and slightly soluble in hydrochloric (lead chloride).
Tim
mantis - 9-3-2006 at 12:50
I have got the same problem with battery acid, after boiling down it turns yellow.
With a small ammount of HNO3 it becomes clear. To get off the nitric acid, you have to heat your H2SO4.
LiveWire - 9-3-2006 at 23:46
Well mine is only yellow when it's hot; it turns back to normal when it cools down.
The precipitate isn't enough for me to be able to do what 12AX7 said. Most of it doesn't fall to the bottom, it's all just a big cloudy mess 
I think I know what it is, though: water soluble inpurities in the battery acid that precipitate when all the water has boiled off.
By the way, is the temperature correct? 320 seems a bit low; I thought it was supposed to reach 337. Is this within the error range of a cheap
thermometer?
YT2095 - 21-7-2006 at 03:01
*BUMP*
I was going to post a finding I discovered today but did a search 1`st and this seems the most likely thread to post in.
Beware, Some car Batts use EDTA in them, that`s what can also be responsible for any micro thin needle like crystals that are almost impossible to
remove from reclaimed battery acid.
this "Plague" has been bothering me for some years now, I`ve been experimenting with EDTA and a variety of metals and salts, and recognised the
crystal form, after a simple google search, I found that it`s quite common practice add EDTA to lead acid batts as a way of prolonging life and in
some cases rejuventaing them completely.
BINGO!
case solved 
tumadre - 21-7-2006 at 14:04
I had the exact same thing happen to me, clear acid at 1.35 grams/ml
turns yellow at about1.5 and black with a white precipatate at 1.8
mine was battery acid removed from a battery that had been over-charged until 1.35 grams/ml
EDTA wtf man!
not_important - 21-7-2006 at 19:25
Note that H2SO4 partially decomposses at its boiling point. I think you might do better by boiling it down in a rig with a vigreux column until the
acid gets up to 88-92 percent, let it cool down, and switch to reduced pressure distallation.
If there are organics in the acid, you can clean some of them up by heating the acid on a waterbath, and adding H2O2 _one_ drop at a time, with
strring and waiting between drops. I've used that to clean up 'drain opener' H2SO4, which generally is brown from traces of organics.
And, yes, battery acid that's been used in batteries will have a little lead sulfate in it, that's what distillation is for.
BromicAcid - 21-7-2006 at 22:09
I also had this same problem before with boiling down acid refills. I boiled down 3 of them and ended up with noticeable yellow crystals at the
bottom of the container I put it in, they started to really show up a few days later, I guess they settled out, at the time I had to wonder if they
were sulfur somehow, kind of looked like it.