I cant stress strongly enough that pickle jars or glass jars of any type are not suitable containers to generate hydroxy gas. The slightest accident is going to turn that glass jar into a glass grenade with the unpleasant side effects that usually accompany such events.
To prevent flashbacks you will need a water trap otherwise known as a bubbler, which also has the added benefit of scrubbing the gas clean of caustic vapours. Dont rely on existing arrestors as used on oxy/acet gas welders, the flame front speed of hydroxy is way too fast for them to contain the flame.
The electrolyte I will be using is NaOh a.k.a. Caustic Soda a.k.a. Sodium Hydroxide. Not baking soda, it creates carbon monoxide and erodes the stainless steel electrodes.
I get mine as caustic soda flake from the hardware store, but it is also possible to get decent quality from other places in drain cleaner form. Make sure if going the drain cleaner route that it doesnt have additives or aluminium shavings added.
Caustic soda is as its name implies very caustic, and rubber gloves will be the order of the day if you dont want to see your skin start peeling away. Its probably also wise to add eye protection too.
Initially I start a cleansing cycle with very dilute 5% caustic soda in distilled water, and then the conditioning phase with full strength 23% NaOh in distilled water which is then the time to keep your wits about you.
Note, I dont use river water or tap water or melted Italian snow water or something sucked out of a rock layer far below the surface. I dont want spiders, bugs and chemicals in my 'lyzer, so its less hassle if I start with the good and clean and fresh stuff...trraaalala.
Dont use baking soda, it creates carbon monoxide and erodes the stainless steel electrodes.
Dont use salt, it gives off chlorine gas, very nasty stuff.