Question on a MacFarland Standards

Judy/Bob Dilworth dilworth at megsinet.net
Sat Mar 6 10:11:37 EST 1999

This is probably why commercial standards outdate after one year!

Judy Dilworth, M.T. (ASCP)

> A problem I have come across since is the need for VERY precise
> conditions on the production of the Ba sulphate suspension. Particle
> size is crucial as is the avoidance of any "inclusive co-precipitation"
> which will affect the "turbidity" of the suspension. The Ba sulphate
> precipitation is used as a quantitative chemical analysis for sulphate
> and anyone interested in the production of standards would be well
> advised to refer to a standard chemical text for the conditions for Ba
> sulphate precipitation. The other consideration is that any inorganic
> suspension is subject to crystaline change over time which is why Ba
> sulphate suspensions must be renewed after a time.
> Peter Harris,
> Soil Microbiologist,
> (who has benefited for decades from the knowledge of chemists)
> University of Reading,
> UK
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