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    Fluids for Bubble Sextants and Sealing Methods
    From: Robert Swartz
    Date: 2015 Dec 27, 23:40 -0800

    The following fluids have been used in bubble chambers for bubble sextants. Their refractive indices and viscosities are similar. However; their volitilities and sealing methods vary greatly:

    1) Xylene-a ring hydrocarbon used in U.S bubble sextants up to late WWII. Easily obtained in most hardware stores. Sealed with clear shellac and teflon seals. Will not seal with neoprene O rings

    as the rings swell and leach coloring. Will not seal with epoxy. Highly volitile.

    2) Hexane-a straight hydrocarbon used in British bubble sextants. Odorless mineral spirits contains hexane and can be obtained in most hardware stores. Can be sealed with O rings and clear two part

    5 minute epoxy. Will not seal with shellac. Volitile

    3) Dow Corning silicone fluid- Proprietary synthetic chemical used from late WWII on in most bubble sextants and as a damping fluid in pendulous mirror sextants. Obtained on Ebay or from chemical companies, Viscosity of 10-20 Cs or in military specs., .65. Seals with epoxy, teflon or neoprene O rings. Least volitile and easiest to work with.

    If you are attempting to restore a bubble sextant, be aware that some WWII manufacturers used Radium pant as a primary or secondary lighting source for the bubble chamber.

    Over 70+ years, the luminous component has deteriorated but the Radium component is still radioactive. I have yet to find a satisfactory substitute for this non-obtainable paint.

    Under no circumstances use water or alcohol to fill bubble chambers.

    I welcome any additions or corrections to this post.

    Robert Swartz

       
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