The experiment any Tesla-coiler simply must do! You just have to put any kind of fluorescent tube near the coil to see it lights itself spontaneously, and without a single wire!
The explanation :
The gas inside the tube bears the high frequency variations of the electrical field, which excites the gas molecules and produces light.
Here on the right side, a standard fluorescent tube erroneously called “neon tube”. Indeed, in the left side, you have a neon tube, which lightens up in orange-pink.
While submitted to the huge voltage of the coil, a piece of glass, one of the best insulators, lets the current pass. exactly if it was a conductor.
This easy experiment shows the conductive character of ozone, which is the gas created after the spark has gone through the air : the spark starts at the bottom, where there is less resistance. It produces ozone and heats up the air. The spark will follow an ascending curb, showing that this zone is more conductive than the surrounding air.
Electrocution of a human body
During our manipulations, more than once did we all put our fingers a little too close from the final electrode and the spark didn’t need coaxing... it sprang and went right through us. Even though this electrocution is not painless, it is not harmful to the human being because the intensity is far too weak for that: even after several electrocutions none of us has ever been knocked out by the shock, nor hurt, nor even slightly burnt. The current of the secondary coil is really harmless!
See video (It's my hand -- But don't try this by yourself)
The spark going through water
After building a rough device, we put electrodes that were connected to the coil under water, thinking it would result into hydrolyse or some other phenomenon. The experiment wasn’t exactly what we expected since nothing happened and the tester was electrocuted …
In order to prepare this experiment, we used the coils of 4 and 5 cm as well as our last two primaries. We wired the two primaries in parallel on the power and got the tip of the telescopic antenna close to the top of the second coil. After a few adjustments, we realised that a wonderful electronic crown was forming itself around the tip of the antenna. If we change the connections of one of the primaries, this crown becomes a very nice and thick electric spark presenting a tail. Unfortunately, we didn’t have anything to immortalize the instant.