40 - To Make Aqua Regis, which Dissolves Gold, and Other Metals from Silver.
Start with nitric acid, as before, which you put into glass flasks. To every 1 pound of acid, for example, add 2 ounces of pulverized sal ammoniac. Put the flask in a pan full of hot water, and with its heat, the ammoniac will soon start to dissolve. Continue to stir the nitric acid in the flask, which will soon dissolve all the ammoniac and will become tinted a yellow color. Add in new ammoniac until the acid dissolves it no more.
Now, leave the acid to settle down somewhat, and carefully decant it clear. Leave the useless sediment of the ammoniac in the bottom. At this point, the acid will become powerful and able to dissolve gold and other metals out of silver, which it does not touch at all.