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Author: Subject: Formaldehyde
Jor
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[*] posted on 24-12-2009 at 18:56
Formaldehyde


I have a liter of 6% formaldehyde here. It is standing in the way so I figured out I have 3 options:

-Trying to concentrate it, to 37%. I think this should be possible by simply boiling the solution, but when looking at the boiling point of formaldehyde (wikipedia) I see 95C, so the gas doesn't simply boil away like when heating ammonia, but the 37% solution seems to be some sort of azeotrope?
-Convert the formalin to paraformaldehyde, and generate CH2O when needed. How can I effectively convert it to paraformaldehyde?
-Bring it to a waste processing facility. The stuff is so cheap that this might be better than all the hassle, but I'm not sure yet.
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Joauml
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[*] posted on 25-12-2009 at 02:58


You could make some hexamine if necessary



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Jor
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[*] posted on 25-12-2009 at 08:22


I already have plenty of hexamine, and I never use it, so I don't need to make more to be honest.
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entropy51
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[*] posted on 25-12-2009 at 11:51


Jor, this old thread has a couple of references that probably have the information you're looking for. There is also a whole book on HCHO in the forum library, I believe.



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ChrisWhewell
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[*] posted on 25-12-2009 at 12:07


I'd be inclined to keep it on hand for silvering glass per Brashear's method, or else oxidize it to formic or a formate salt for later use in reducing platinum group metals from solution.
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JohnWW
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[*] posted on 25-12-2009 at 12:36


That 6% solution of formaldehyde may be about what embalmers in funeral homes use for embalming bodies, by replacing all the blood. However, it is definitely much weaker than the "formalin" used for preserving biological specimens in, which is 40% formaldehyde.
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Panache
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[*] posted on 25-12-2009 at 16:03


It condenses at -21C, so you could condense the gas over a dry ice cold finger, then dilute it down accurately to 37%. Either way i'd somehow keep it if possible its getting quite rarer these days, although its not difficult to make.



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entropy51
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[*] posted on 25-12-2009 at 18:20


Quote:
However, it is definitely much weaker than the "formalin" used for preserving biological specimens in, which is 40% formaldehyde
No, John, 40% is usually diluted to about 4% for fixing and preserving biological specimens.
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Klute
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[*] posted on 10-1-2010 at 14:06


The best way of making paraformaldehyde is to distill formalin solutions under vaccum until take off nearly stops, then pourin g the thick residu onto a cold pyrex dish and breaking up the gummy solid that forms. Be carefull to not let it settle in the distillation flask as it makes a very hard solid when cold, and you will not be able to scrap it out (beleive me, I broke a flask trying to :( )



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