Re: Thoughts on B5

From:Bryan Llewellyn <>

I suspect the addition of sodium acetate to formol sublimate to make B5 came
about to ensure mild alkalinity of the solution.  This ensures the "correct"
type of fixation.  According to Baker, it reacts differently in acid
solution.  Unfortunately, a precipitate forms overnight, so the solution is
discarded after use.

If alkaline (hard) tap water is used to make up formol sublimate, my opinion
is that the sodium acetate is not needed.  I have never been able to tell
the difference between them.  The advantage to using formol sublimate over
B5 is that it can simply be filtered and re-used, thus avoiding most of the
problems of disposal.  Filtering the fixative consumes about 1 mL per use
instead of 50 mL, the rest being recycled.  I have used formol sublimate in
this way for decades (actually since 1962) with nary a single complaint
except this last year.  Accreditation inspectors ordered me to stop re-using
formol sublimate and switch to B5 on penalty of losing our anatomic
pathology accreditiation.

Incidentally, has there ever been a study comparing the two fixatives for
morphologic and histochemical use?  What would happen if the precipitate
from B5 were filtered out and the solution re-used?  How would the results
compare to fresh B5 and to formol sublimate?

Bryan Llewellyn

----- Original Message -----
From: "Histomail\" <>
To: <>
Sent: October 29, 2000 2:57 PM
Subject: Thoughts on B5

> Dear Colleagues,
> I've always wondered why we add Conc. Formalin to our Sodium
> Acetate/Mercuric Chloride solution immediately before use.?
> Is it because it was necessary with Helly's, which used to oxidise and go
> off rather quickly - appearing muddy brown etc.?
> If we never had to bother with Formal Sublimate, why are we so concerned
> with the Sodium Acetate in B5? Is there a reaction?? Or not??
> Mike Rentsch. Histomail

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