From: Greg Ralston <gregr@biochem.usyd.edu.au>
  To  : rasmb@bbri.eri.harvard.edu
  Date: Mon, 17 Jul 1995 09:31:53 +1000

Vinylite gaskets

Dear XLA-ers,

While we are on the subject of maintenance and the like, I am reminded of a 
long-standing problem:

Is it better to replace the vinylite window gaskets for each run, or is it 
better to let the windows bed down and to reuse the gaskets? 

On a limited budget, I am very conscious of the cost of replacing windows, and 
the relative costs of windows and gaskets, so we tend to use new vinylite 
gaskets each run. My gut feeling is that the use of a fresh gasket will better 
absorb tensions between the window and the window holder. One might argue that 
once the window has bedded down there will be an optimal fit between gasket, 
holder and window (provided that the gasket or window aren't shifted). We go 
through thousands! I've tried cutting some from shower-curtains, but they are 
too soft.

What is the consensus out there?  Do most users use fresh gaskets, or do they  
keep using old ones? How many people find themselves going through large numbers
of windows? What is the life expectancy of a quartz window? (All of our new ones
are still going strong after two years, but some from model E days have had it.)

On the subject of cleaning light-sources: Rotation of the light source to 
achieve maximum illumination (or uniform illumination) will change the angle of 
incidence of the light beam, such that light may no longer be parallel with the 
meniscus. What is the best way of checking this orientation? Can the source be 
rotated while the chamber holds a vacuum? Or should one do these tests at low 
speed without a vacuum? Yet at low speeds, the meniscus will not be vertical.

In the Model E, the interference camera was focussed on the 2/3 plane of the 
cell. Where is the camera lens focussed in the XL-A? If one wants to use shorter
optical path-length cells, is it wise to use a spacer to get the 2/3 plane (or 
the midpoint?) up at the focal length of the slit lens? Or doesn't it matter?


Jack, for cleaning the XL-A lamp, we have found that Colgate regular mint taste 
works well. In the toothpaste world, we are in the grip of the multinationals; 
there are no specifically antipodean toothpaste maunfacturers that I am aware 
of. 


Cheers,

Greg Ralston




Greg Ralston

Phone (61 2) 351 3906
Fax   (61 2) 351 4726

e-mail: G.Ralston@biochem.usyd.edu.au 

Department of Biochemistry
University of Sydney
Sydney, NSW, 2006
Australia