Platdigger,
The standard sulfuric parting starts with a solution of 100ml concentrated H2SO4 + 22 ml distilled water (90%, by weight, boiling point = 504 F). A second parting uses a solution of 100ml H2SO4 + 10ml distilled water (95% by weight, boiling point = 563 F). Both are used very hot - near boiling, but not quite. The first parting is very slow and is used to prevent the Pt and Au from breaking up. The second is much faster. Some people use only the 95%. These solutions will dissolve Ag and Pd but not Au or Pt.
Two containers of pure tin and pure bismuth are placed on the hot plate to control the temperature. Tin melts at 450F and bismuth at 520F. The 90% is heated until the tin melts but the bismuth doesn't. The 95% until the bismuth barely melts. I think we used to put these metals in Coors porcelain crucibles. It's been a long time since I've done this.
These figures came from "A Textbook of Fire Assaying" by Bugbee. They are based on using reagent grade sulfuric. Technical grade is usually a percent or two weaker to start with. I used only the 95% sulfuric.
These are only the basics. There are detailed ways to rinse out the silver sulfate and to remove traces of lead retained in the assay beads. Etc.
The standard sulfuric parting starts with a solution of 100ml concentrated H2SO4 + 22 ml distilled water (90%, by weight, boiling point = 504 F). A second parting uses a solution of 100ml H2SO4 + 10ml distilled water (95% by weight, boiling point = 563 F). Both are used very hot - near boiling, but not quite. The first parting is very slow and is used to prevent the Pt and Au from breaking up. The second is much faster. Some people use only the 95%. These solutions will dissolve Ag and Pd but not Au or Pt.
Two containers of pure tin and pure bismuth are placed on the hot plate to control the temperature. Tin melts at 450F and bismuth at 520F. The 90% is heated until the tin melts but the bismuth doesn't. The 95% until the bismuth barely melts. I think we used to put these metals in Coors porcelain crucibles. It's been a long time since I've done this.
These figures came from "A Textbook of Fire Assaying" by Bugbee. They are based on using reagent grade sulfuric. Technical grade is usually a percent or two weaker to start with. I used only the 95% sulfuric.
These are only the basics. There are detailed ways to rinse out the silver sulfate and to remove traces of lead retained in the assay beads. Etc.
