pycnometers

Bill Melchior, NCTR/FDA WMELCHIOR at NTET.NCTR.FDA.GOV
Fri Oct 9 08:33:50 EST 1992


>Pycnometers are devices which allow precise determinations of
>volume.
>Does anyone have any knowledge or experience with these?
>There are liquid displacement type instruments and air/gas
>comparison types.

I assume you want to measure *density* rather than volume.  How you do it
depends on what, why, and how often. 

I haven't used a real pycnometer for many years.  I have used the classical
glass bulb with capillary stopper -- my recollection is that it worked fine
but was tedious and of course required large volumes.  I also did a little
work with one of the electronic units (vibrating tube filled with liquid) 
-- I remember having problems with the calibration.  If you have many 
samples of adequate volume, this would be the easiest, but prepared to 
spend both $$ and time in calibration.  (As stated, these experiences were 
20-30 yrs ago; perhaps the electronic units are easier to use now.  
Comments from other users are welcome.)

What I currently do for checking CsCl solutions is to use a siliconized 100
microliter glass capillary pipet, weighed with and without the solution. 
I figure it's good to a fraction of a percent.  It's definitely easier than 
using a refractometer, and non-destructive.
________________________________________________________________________________
The opinions stated are mine, not those of NCTR or its sponsoring organizations.

Bill Melchior                                ||     OMNISCIENCE
National Center for Toxicological Research   ||    Knowing what
Jefferson, AR  72079                         ||    thou knowest not
(501) 543-7206                               ||    is in a sense
                                             ||    omniscience.
WMELCHIOR at NTDOC.NCTR.FDA.GOV                 ||       from Grooks, Piet Hein



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