। ॥ ५९ ॥
In plain words
So this comparison will not hold. Let time pass and the elixir's potency drains away — and the golden colour that had climbed onto the iron is destroyed with it.
Close to the Sanskrit
That — this — becomes not fitting: when that potency of the elixir has gone in the course of long time, the golden colour mounted upon the iron also comes to utter destruction.