jnanian: the reason there are a lot of "herp/derp you will die posts"
is because often times people who have no idea what they are doing
make their own silver nitrate or use cyanide &C thinking
everything is safe and dandy ...
if the OP didn't have a fume hood
he would probably be dead by now ...
John, I must respectfully disagree. I think that the reason for all of the "...you will die" posts is that few, if any, of the readers have any real practical experience. The ratio of posts describing hypothetical consequences to posts describing actual first-hand knowledge is therefore very large. (It is also human nature to remember the dramatic rather than the mundane, so people remember that "cyanide will kill you" after they have forgotten--if they ever knew--what a dangerous dose is and what it would take to experience that dose).
I encounter this routinely.
Challenge: "You are going to use carbon dioxide? Don't you know that it will suffocate you?"
Response: "I'm going to have one cubic foot in a cylinder, in a room with a volume of about 4,000 cubic feet. There's probably already more carbon dioxide in the air in the room than I could add if I emptied the cylinder all at once---even without the air conditioning ventilation."
Reply:" So? And your point is...?"
kq6up: When I gather enough of the dry black sludge. I am going to fire it in an iron (reducing) crucible with an Air-Acetylene torch. That should yield pure metallic Silver.
I think that you would be better served by a graphite crucible; molten silver may wet the iron, and if it does you will lose some as well as have a tough time getting the rest out. From a thermodynamic standpoint, there is no need for a reducing environment; silver oxide becomes unstable with respect to oxygen and silver at temperatures well below its melting point. On the other hand, silver sulfide will melt without decomposing (hence the potassium nitrate addition) and metallic silver will dissolve a considerable quantity of oxygen while molten, much of which comes out of solution as it freezes (a phenomenon known to us alchemists as "spitting silver"). So an oxidizing flux (potassium nitrate, possibly with some borax to help the silver globules coalesce) which excludes atmospheric oxygen might be just the ticket.
Regarding current sources: if you are not in a hurry, just put a high-voltage supply in series with a large balllast resistor (say, 60 VDC in series with 100,000 ohms, for 0.6 milliamps). The current will be nearly constant unless the effective cell resistance rises to a value that is a decent fraction of the ballast resistor value. Even a cheap low-range voltmeter will let you follow the process by watching the cell voltage.
To get a dense silver deposit rather than flakes or dendrites, keep the current density low and try adding an inert thickener (gelatin or dextrin) to the solution.
If you have access to a chemistry lab that is equipped for qualitative analysis, I'd be interested in knowing what concentration of silver would be left in solution by a small excess of ammonium polysulfide or sodium sulfide. At first glance, this would seem to be a reasonably simple and environmentally friendly way of retrieving the silver.
And for the "herp/derp you will die crowd" Yes, hydrogen sulfide toxicity is comparable to that of hydrogen cyanide, but there is a reason why people have survived long enough to report that hydrogen sulfide smells like rotten eggs and cyanide smells like bitter almonds....