Re: way crystallization is induced ?

From: Farooq (farooq_w_at_hotmail-dot-com.no-spam.invalid)
Date: 07/27/04 

Date: 27 Jul 2004 08:28:35 -0500

> Richardwrote:

>
>
> I took organic analysis back in the mid 60's. We didn't have much
in
> the way of analytical equipment available back then- mostly an old
PE
> infrared spectrophotometer. We made derivatives of our unknowns
and
> recrystallized them so we could get melting points.
>
> I recall a small lab in the basement of the chemistsry building,
ether
> boiling away next to the bunsen burners... Late at night
frantically
> scratching away at a beaker or flask with a glass rod trying to get
> something- anything- to precipitate so I could dry it and get it in
a
> melting point capillary tube.
>
> Ahh, the good old days.
>
> Richard

The very same torturous but pedagogically good methods are still in
vogue in developing parts of the world. Infact one of the students
died of third degree burns because of a bunsen burner placed nearby a
flask containing benzene caught fire in the organic lab.

Returning to the original question, the common reasoning given for
scratching the bottom/ walls of the vessel is that the minute rough
surfaces serve as crystallization points . Somewhere else it was
written that scratching releases micro-particles of glass which serve
as nuclei or seeds. This argument can be supported by the fact that
even dust particles can induce crystallization.