Made several experiments and wrote a small article.
http://odontologija.com/wiki/index.php/Aukso_kokybin%C4%97_analiz%C4%97_%28eksperimentas%29#Testing_previously_concentrating_with_copper
==Testing directly with SnCl2==
The aim of this experiment was an approximate evaluation of SnCl2 test sensitivity for detecting Au in acidic solutions and influence of copper on gold detection. I took Au:Cu in ratio as 1 to 1000 and dissolved it in aqua regia. After that I prepared 1:20000, 1:50000, 1:100000, 1:200000 and 1:500000 gold solution (copper was present in all solutions in 1000-fold concentration, as gold).
Immersed similar filter paper pieces into all of these solutions and added approx. equal quantity of SnCl2. After an hour rinsed the pieces with plenty of water and observed them. Here are the results.
Due to poor photo quality, it is almost impossible to see purple stain on 1:100000 paper, but I can easily see it with my eye. Even more, very very pale sign of discoloration could be observed on 1:200000 paper, but it is not visible on photo, and I decided not to show it. 1:500000 paper shows no observable color change.
The interesting fact is, that it is quite difficult to observe purple even on 1:50000, if I havent washed it with water after reacting with stannous chloride. After washing purple becomes clearly visible.
==Testing previously concentrating with copper==
I noticed, that immersing copper wire into solutions with very small concentration of gold, makes copper get dark after a long time. The other part of the experiment will be dedicated to detecting very small amounts of gold in solutions, much more diluted as 1:100000.
The same solutions were canned to 5 different bottles, and 5 copper wires were immersed into each solution.
After several hours wires were removed. All the wires changed their color to almost black, most intense black were observed on the wires removed from the lowest concentration solutions. Wire removed from 1:20000 and 1:50000 solution was visually thinner.
After that I take a little piece of filter paper and tried to wipe off this black outer layer with this piece or paper. After this was completed, I put equal amount of aqua regia on each paper, warmed them and leave for a little time to react. After 10 minutes I washed all these papers with water and pictured them.
http://odontologija.com/wiki/index.php/Aukso_kokybin%C4%97_analiz%C4%97_%28eksperimentas%29#Testing_previously_concentrating_with_copper
==Testing directly with SnCl2==
The aim of this experiment was an approximate evaluation of SnCl2 test sensitivity for detecting Au in acidic solutions and influence of copper on gold detection. I took Au:Cu in ratio as 1 to 1000 and dissolved it in aqua regia. After that I prepared 1:20000, 1:50000, 1:100000, 1:200000 and 1:500000 gold solution (copper was present in all solutions in 1000-fold concentration, as gold).
Immersed similar filter paper pieces into all of these solutions and added approx. equal quantity of SnCl2. After an hour rinsed the pieces with plenty of water and observed them. Here are the results.
Due to poor photo quality, it is almost impossible to see purple stain on 1:100000 paper, but I can easily see it with my eye. Even more, very very pale sign of discoloration could be observed on 1:200000 paper, but it is not visible on photo, and I decided not to show it. 1:500000 paper shows no observable color change.
The interesting fact is, that it is quite difficult to observe purple even on 1:50000, if I havent washed it with water after reacting with stannous chloride. After washing purple becomes clearly visible.
==Testing previously concentrating with copper==
I noticed, that immersing copper wire into solutions with very small concentration of gold, makes copper get dark after a long time. The other part of the experiment will be dedicated to detecting very small amounts of gold in solutions, much more diluted as 1:100000.
The same solutions were canned to 5 different bottles, and 5 copper wires were immersed into each solution.
After several hours wires were removed. All the wires changed their color to almost black, most intense black were observed on the wires removed from the lowest concentration solutions. Wire removed from 1:20000 and 1:50000 solution was visually thinner.
After that I take a little piece of filter paper and tried to wipe off this black outer layer with this piece or paper. After this was completed, I put equal amount of aqua regia on each paper, warmed them and leave for a little time to react. After 10 minutes I washed all these papers with water and pictured them.
