Good Morning HistoNetters from snowy Massachusetts!

Russ Allison asked:
>Our microbiologists from time to time microwave small (50 - 100
>ml) amounts of culture media in conical flasks with non-absorbent
>cotton wool in the necks.
>Recently, there was a smell of burning from the oven and when
>taken out, the cotton wool was "burnt" and smelled like it.  There
>had been no flames (sorry about the English of that sentence!)
>I believe I am right in saying that cotton contains oil.
>May that have been the cause and how come, after the many
>hundreds of times we have done it, the wool burned that time?

I wouldn't suspect oil, because oil, like fat, is a poor absorber of
microwaves.  Any time there are different materials in a microwave cavity
(like the cotton wool and the culture media), they are going to heat at
different rates, due primarily to the relative polar structure of the
molecules.  My guess, in this case, is that the culture media heats faster
than than the cotton wool and that all goes well when there is sufficient
media in the flask for the amount of energy produced.  However, as soon as
the media has reached a threshold and has absorbed all of the microwave
energy it can, the energy microwaves begin to heat the next best thing, in
this case, the wool.

Best regards,
Steven Slap
Forensic Microwaver



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Steven E. Slap
Marketing Manager & Microwave Product Specialist
Hacker Industries & Instruments
413-733-3808
http://www.hackerinstruments.com
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