Contaminants at the bottom of Ethane tanks

[Bob Grassucci]

Hi All,
	We have run into a problem with contaminants on our frozen hydrated grids 
which we believe come from residue that is stirred up in the ethane tank 
when it is close to empty.  Does anyone have experience as to what the 
minimum pressure of the tank before one stops using it?  We are using Grade 
5.0 ethane and the small bench top bottles (2.0 lbs?) .  They generally 
start out at 650 PSI when they are full.  Is there a rule of thumb that 
people are using?  The contaminant's appearance is very high contrast 
usually round spots which most people I have spoken with attribute it to 
ethane but if it were ethane it should evaporate in the column but it does 
not.  Thanks for your advice.
	Regards,
	Bob

Robert Grassucci
Howard Hughes Medical Institute at The Wadsworth Center
Empire State Plaza
Albany, NY 12201-0509
Phone: (518)474-5821
Fax: (518)486-2191
E-Mail: bobg at wadsworth.org
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