goldsilverpro said:
I don't think his anode tray slid back and forth. I think he removed it when he harvested the crystal. Harold could probably give the pros and cons of his design.
My tray could slide, but not without raising a portion out of the electrolyte. That was very acceptable because the cell is inactive when scraping down the crystals. I used to park it at the far end while scraping the crystals. The bottom of the tray sat on the end of, but inside the cell, therefore catching any drips.
As far as my design is concerned, I would likely do a few things differently, although the cell functioned perfectly well. The only negative aspect of my cell was that the sides were in close proximity to the anode. That resulted in shorting of the cell prematurely. I dealt with the problem by applying a band of black vinyl tape along the top edge, which then wrapped around the inside down about 1½" beyond the depth of the electrolyte. That discouraged shorting adequately. You can see the tape in the photo that is posted, below.
The design had two positive aspects, which is the reason it was chosen. The only cell I ever witnessed was almost identical to mine, aside from having four sides that sloped away from the center. That eliminates the premature shorting, but also increases the volume of electrolyte, plus it makes sealing the cell all the harder. I kept plastic covers on both ends of my cell when it was in operation, to minimize the possibility of contamination dropping in with the silver.
I'm sure that the 4.75" solution depth was determined as the ideal compromise to maximize production after data from 150 years of its history. Actually, most any other depth could be used, but there would be a sacrifice, one way or another.
I'm afraid I'd have to agree. My electrolyte depth was only about 3 or 3½". Shorting was a distinct possibility. Because the cell ran continuously, I cut back on amperage so the deposit was slower, thus extending the time intervals between knocking down the crystals. Added depth, coupled with a greater distance to the sides of the cathode would certainly be beneficial, but as Chris stated, every change is a trade-off. Pretty much ANY design will function to some degree.
My advice is to design a system around the projected volume that is to be processed. You are far better served to operate a small cell for extended periods of time, requiring small amounts of silver for electrolyte, than to operate a large cell, which may produce profusely, but requires a huge amount of silver for the electrolyte. Should volume increase in the future, it's easy enough to add a second cell.
When designing your cell, I would also keep in mind the distance between the bars and the sides of the tank. Sometimes, under certain circumstances, very long thin crystals can grow, which can bridge from the tank to the bars. The worst thing that can happen is to create a short. It can start a fire. If a hole burns in the cloth, the undissolved sludge (gold, slag, etc.) can dump into the solution and drastically contaminate it. The solution will require filtering, the tank will require disassembly and cleaning, and the silver crystal will have to be melted and rerun.
Yep, what Chris said. I experienced shorting, enough to burn a hole in one filter bag. I was fortunate in that there was no fire. Be advised that cotton, when soaked in silver nitrate, is very eager to burn, and will do so even when wet. Fire is a real possibility, although not to be feared under normal conditions.
The one place I differ is crystal. Impure crystal can be run perfectly well in a cell without melting, is so desired. I re-ran crystal a few times when I found I had run my cell too long and had copper co-deposited with my silver. Simply wash the crystal well (distilled water), then place in the filter, covering with an anode. You'll discover that the crystal will process perfectly well, and create very nice new crystal on the anode. Bottom line is there is no need to melt the crystal. I would NOT advise cement silver be processed the same way. Too much garbage is removed in the melting process, for cement silver is rarely of high quality, unlike crystal that has already been through the cell once.
We have been discussing a Balbach-Thum horizontal cell. There are also Moebius vertical cells that are widely used mainly because they take up less floor space. However, they are more complicated to use and the anode stubs have to be remelted and rerun. Also, removing the crystal is more difficult. The Balbach-Thum (usually just called a Thum cell) horizontal cell is the simplest to set up and use.
Chris and I are in lock-step on this issue. The cell described is the fastest and easiest to build and to operate.
Nice job, Chris.
For the record, my tank was made of 304 stainless, with TIG welded corners. 316 would be slightly better for chemical resistance, although that is a non-issue for a silver cell. Either material is an excellent choice. I had it electropolished after it was welded. Unseen in the photo, there is a lug welded to the back side upper right hand corner, to which the cathode lead is connected via a large clip. Contact with the anode is made with a silver "candle stick" electrode. I made a simple cast iron mold that poured a round disc of silver, roughly 3/4" thick x 1" diameter, with a ¼" stem, to which the anode lead was attached with a clamp.
Harold
