goldsilverpro said:
Takes about 1.22ml of 70% nitric acid plus 1.22ml of distilled water to dissolve 1 gram of silver. This is not exact and will depend on your setup. For example, if the dissolving container is covered, it could take less.
Chris, I have used this figure (1.22ml concentrated nitric acid) and it dissolved all the sterling in the batch completely.
But when I added copper to begin cementing, there was much free nitric acid still left and it consumed my copper and produced visible brown fumes. The solution became very hot. Also the silver began to float and it was re-dissolving as soon as it cemented. The resulting cement silver was very finely divided and hard to clean.
If I want to dissolve 500 grams of sterling I begin by incinerating the clean sterling and adding it to 500ml of distilled water in a suitable heat resistant container.
Then I begin adding concentrated nitric acid in 50ml increments on low heat, tapering off the amount added toward the end of the reaction and increasing the heat. As always, I cover my container with a saucer or lid or watch glass.
I know that the nitric acid has been nearly completely used when there are no more brown fumes in the heated reaction container, and there are a few bits of undissolved sterling left in the bottom of the container.
Sometimes I will overshoot and end up with no sterling bits left. If this happens, then I'll add a few more pieces of sterling to the hot liquid and wait until the acid is used completely.
With 500 grams of sterling as in this example, I have used as little as .7ml to as much as a little over 1ml of concentrated nitric acid to get the sterling dissolved as described above.
This procedure can consume the nitric acid so completely that the silver will not cement when the copper is added to the solution. Some free nitric is required to get the cementing reaction started. If this happens, then I can add a few drops of concentrated nitric acid and stirring to get the cementing reaction going.
While this process takes a little more time, it does cut down on the amount of nitric acid I use and the amount of waste created.
Not to impune what you have calculated or written, but to help the newcomer who may have spent much time painstakingly making their own nitric acid, or paid as much as $100 for a half liter of nitric (like I did when I first started refining).
Respectfully, kadriver