The Mercury Injector improves operator safety and dispensing accuracy. Pressing a button advances a plunger, dispensing 10 micro liters (100mg) or mercury, equivalent to a ball 2mm in diameter-the correct amount for most argon filled “neon” tubes. The reservoir has a 500 micro liter capacity, good for 50 applications. Marked in 10 micro liter increments, it enables the user to calibrate total volume by setting the plunger position. The injector dispensing tube end is blunt, reducing the danger associated with sharp medical syringes commonly employed to inject mercury. In addition, it offers the repeatable accuracy needed to prevent over-filling that causes mercury condensation tube darkening, and under-filling that reduces tube brightness.