We've had a set of ancient Vance & Hines mercury carb stix for decades.
The four silicone rubber vacuum tubes have been removed in the both pics, and the back cover removed from the housing to show the bottom reservoir & tops of the capillary tubes sans rubber tubes.
The past few years we've been seeing occasional, random air bubbles / voids in the mercury columns.
The voids run anywhere from 2 to 4 mm long. They can appear in different positions in the column if vacuum is removed & reapplied. Or not at all. Occasionally there may be two voids in a column. It's very random. The reservoir is full to the top & the vent is unobstructed. We decided to clean & rebuild.
Drained the reservoir & filtered the merc through a tiny hole in a paper filter, a method we found researching how to clean a small quantity of merc. We did so because a layer of oxidation that looks like slag sat on top of the merc. The paper caught the layer of oxidation & held it on the sides of the paper filter while clean, shiny liquid merc dropped into the glass storage vial. The glass lab vial, capped & set aside. It's about 2 fl.oz., or 59ml. In volume.
Removed the cap from the reservoir, and the capillary tubes from the cap. Cleaned the inside of the reservoir tub and the outside of the capillary tubes.
Capillary passages themselves appeared clean, which is a good thing. At about 0.025”, or 0.635mm, we'd have no way to clean the minuscule passages, and they're capped at the top with some sort of porous sealant anyway. More on that later.
Reassembled & resealed the cap to the reservoir tub with a two part adhesive suitable for polyethylene. Reinsert the tubes evenly into the reservoir cap & seal with blue RTV. Inserted the tube/reservoir assembly into the housing. Pressed the silicone vacuum tubes onto the top of the capillary tubes after warming them to soften. Refilled the reservoir with the cleaned merc using a pipette to introduce it into the vertical vent tube a tiny portion at a time. Tedious. Test for vacuum leaks with a vacuum pump set to hold vacuum to make sure there were no vacuum leaks. No voids were seen. Vacuum held constant on all 4 tubes.
Bag & take everything that touched merc to the local HazMat disposal site.
Done.
All work was done safely & cleanly as possible outdoors wearing nitrile gloves. There were no spills or gottaway beads.
A curiosity question for the old-timers:
When we removed the silicone rubber vacuum tubes from the tops of the glass capillary tubes we noticed white material of some sort covering the top 10mm or so of each tube. It's quite hard & very well adhered to the glass itself. Won't scratch with a fingernail. Seems ceramic-like. It has to be porous, because it flows air. Otherwise no mercury could be drawn into the capillaries by vacuum.
Out best guess is, it's there to keep mercury from being drawn out the top of the tubes. We're not gonna attempt to remove it, but we're curious; anyone know what the white material is?
Good Ridin'
slmjim & Z1BEBE