IN-18 What is between Pins 1 and 8?

[Larry Willson]

I recently got some IN-18 nixies and noticed an internal coil/wire between pins 1 and 8. What is it? 

In one of my tubes the wire has come disconnected and loose inside the tube shorting digits together.

Thanks

[Paul Andrews]

It is a capsule that contained mercury. It was heated up when the tube was manufactured to release the mercury. The addition of mercury to the tubes vastly extends their lifetime.

[Larry]

Thank you to everyone that responded with the answer. Never would have guessed this. To follow up; is it common for the capsule and wire to come loose and float inside the tube? Depending on where the wire rests it shorts digits together.

[gregebert]

Unlikely. I have fourteen IN-18's in my kitchen clock, and none has failed. These are extraordinary tubes that look great and last a long time.