I've been using that process all summer to remove rust from flathead engines. To the water I do add sodium carbonate, Arm and Hammer Washing Soda. Do not use baking soda as that's sodium bicarbonate, and don't use their laundry detergent. It's a bit hard to find but I get it here locally at Fred Myers. Sodium carbonate allows the current to flow through the water. I used a 12 vold 6 amp battery charger and you can see that when the washing soda is added the conductivity is increased.
Also, In addition to scraping off the crude on top of the water (make sure power is off). You need to clean the electrode rods as they get covered with the rust that is being removed from your object. Make sure all grease and oil is off the object or it will not be as affective
For those of you that want to quickly "antique" a metal part, connect the positive lead to the part you want to "antique" and the negative lead to a piece of rusty metal. Check it every hour to determine if it's to your satisfaction.
I love this process. My only change would be to increase my the amps I use. Remeber this fact. ***********0.1 amp can kill**********
Sid