A question and two replies

Question

To Labsafety-L discussion LABSAFETY-L@SIU.EDU on 12/11/2003

We are trying to eliminate the use of mercury on our campus but some researchers are having difficulty finding alternatives. I have no experience with mercury bubblers and would appreciate any information that you may have regarding an alternate. A researcher is working with highly oxygen and water sensitive materials, and conducts most reactions under a nitrogen atmosphere using a vacuum line. All vacuum lines he uses have a mercury bubbler attached to the end of the line that provides a slight overpressure within the apparatus. The overpressure is essential to atmospheric leaks through connections, and also provides a method for transferring liquids between containers by using the gas pressure. Conventional mineral oil bubblers do not provide this capability, and the researcher has spent quite some time investigating possible designs for mineral oil bubblers that would provide the overpressure. However, he has not found a design which provides these capabilities, and I was wondering if you have any suggestions that may help.

Thanks for your help and I appreciate any information that you may have regarding an alternative to the mercury bubbler.

Answers

I did several years of research on highly water, oxygen and temperature sensitive organometallic compounds myself using inert gas and vacuum techniques before changing to an office job. A lot of vacuum line techniques were carried out without a bubbler using high vacuum and cryopumping. Argon was used instead of nitrogen as an inert gas and for transporting liquids compunds. Very dry and of high chemical resistance (even to F2, OF2 ...) are perfluorinated oils (Kel-F), they could be used to get a slight overpressure (a higher column to be used than in a normal bubbler, if a). For a higher pressure the bubbler can be equipped with an adjustable pressure relieve valve (they are available for the laboratory made from glass with ground glass joints). At the moment we are using an adjustable spring loaded type in our laboratory that works quite well. I hope your researcher can use some of the information for his problem. 

Dr. T. H. B.
Head of the Department for Chemical and Biological Hazards
Berufsgenossenschaft der chemischen Industrie
Kurfürsten-Anlage 62
69115 Heidelberg   Germany

A lab here replaced their mercury bubblers with mechanical check valves.
J. L.G.     University of North Carolina

I would recommend the researcher consider re-designing her/his system to allow for the slight over-pressurization through a completely different method. Don't change the fluid, change the gizmo.

Perhaps a mechanical system would work? It would be more money up-front than filling a tube with liquid mercury, but would eliminate the Hg.

We have countless systems here that need positive or negative pressure, and all of them are controlled mechanically.  Suggesting this to your professor is giving her/him a very large selection of things to choose from, I believe.

E. T.
BioPort Corporation
3500 N. Martin L. King Jr. Blvd.
Lansing, MI 48906