Passing electrodes through glass

[THX-1138]

I picked up some odd glassware at a surplus place -- about 50ml, but with no bottom -- and I'd like to try turning one of them into a Jacob's ladder column. The challenge is how to pass the wire through the (flint) glass wall of the bottle for an external connexion.

 

How does one pass a wire through a glass interface, keeping a good seal? Like a connector passing out of the bottom of an old television valve?

 

Thanks!

[SH3RL0CK]

You have to melt the glass around the wire.

[THX-1138]

Um, yeah, that much is kinda obvious. But to what radius do you soften the point of penetration; should the wire be heated (and to what degree) as well; how do you assure the glass will adhere to the wire; etc..

[John Cuthber]

You need to use the right metal for the glass too. If not then differential expansion on heating will crack the joint when it cools.

There's an alloy caled kovar that is used for this trick for borosilicate glass IIRC platinum works for some varieties of glass too. (There are other ways too but this problem is an art in it's own right).

A cop-out way to do it is to use a glass seal that someone else has made, like an old TV tube or light bulb. You still have to match the expansion coefficients though.

[doG]

As a side note, if you're in the U.S., Jacob's Ladders are a source of broadband RF radiation which can cause quite a bit of interference for radio and TV. If you run it too much the FCC could come knocking on your door.

[SH3RL0CK]

I'm not sure but this might be more art than science. I would suggest you experiment. You could try a few things (on other glass samples with varying sizes and types of wires) to see what works and what doesn't.