§ 66. Helvetius's Gold Assayed.
"The rumour, of course, spread at once like wildfire through the
whole city; and in the afternoon, I had visits from many illustrious
students of this Art; I also received a call from the Master of the Mint
and some other gentlemen, who requested me to place at their disposal a
small piece of the gold, in order that they might subject it to the
usual tests. I consented, and we betook ourselves to the house of a
certain silversmith, named Brechtil, who submitted a small piece of my
gold to the test called `the fourth': three or four parts of silver are
melted in the crucible with one part of gold, and then beaten out into
thin plates, upon which some strong aqua fortis [nitric acid] is
poured. The usual result of this experiment is that the silver is
dissolved, while the gold sinks to the bottom in the shape of a black
powder, and after the aqua fortis has been poured off, [the
gold,] melted once again in the crucible, resumes its former shape....
When we now performed this experiment, we thought at first that one-half
of the gold had evaporated; but afterwards we found that this was not
the case, but that, on the contrary, two scruples of the silver had
undergone a change into gold.
