This section is from the book "Leaching Gold and Silver Ores. The Plattner And Kiss Processes: A Practical Treatise", by Charles Howard Aaron. Also available from Amazon: Leaching Gold And Silver Ores.
189. By taking some of the waste liquor from the gold tub, filtering twice through Sweedish paper, and then smelting the paper with litharge, I found that after 24 hours settling there remained gold in suspension, equal to $1.00 in value for each ton of ore leached. After 48 hours I still found half that quantity. The filtrates from these tests were boiled with zinc until all precipitable metals were thrown down. The precipitate contained no gold, which shows that iron perchlor-ide does not dissolve gold in presence of the iron proto-salts, thus setting at rest a doubt which had arisen, as to whether or not the precipitated gold might be, to some extent, re-dissolved by remaining for many hours in contact with the solution of iron persalts, which is produced when gold terchloride is decomposed by iron proto-sulphate.