Forming hydrogen sulfide from electrolysis of sodium thiosulfate So I was doing electrolysis on two silver electrodes and sodium thiosulfate. 
Some observations


The voltage drops extremely fast from 2 V to less than 1 V in 15 minutes, possibly because of the thiosulfate reduction.
Gases are liberated out of solution.
The solution turns black quickly.


Alert: I am using a fume hood.

Since I'm afraid of this spoiled eggs smell I just want to know if I am in any way creating hydrogen sulfide? Just want to be sure that the gas is tetrathionate and not hydrogen sulfide.

My other concern is with the voltage. How can I keep it from dropping so fast?
Yup, you're forming sulfide.

Render the thiosulfate ion as $(\ce {S-}-\ce {SO3-})$.  Then at the cathode:

$(\ce {S-}-\ce {SO3-})+2e^- \rightarrow \ce {S^{2-}}+\ce {SO3^{2-}}$

Both products are basic, with sulfide ion being strongly so,  and they will react further with protons; so the sulfide ion gives some hydrogen sulfide.  Sulfide ions can also combine with silver ions, from the anode, giving a black precipitate.  The other product, sulfite ion, can be reduced further, possibly forming still more sulfide ion/hydrogen sulfide.

So the reaction is not safe.  But kudos for using a fume hood.