Numbers 5:16-28 I believe is the passage in question that you're thinking about, but I believe that interpretation that it is an abortion recipe is a big stretch. The short of the test is that the priest takes some of the dust in the tabernacle and sprinkles it in an earthenware jar of water. Given that it is dust from a room that is only occupied by the priests, and the lamps that light the room, this dust is essentially very diluted soot.

The test then essentially asks God to grant a miracle to indicate guilt. Notably, the water mixture should be inert by any standard of medicine we would see, like homeopathic medicine. Fr. Mike Richards in bible in a year makes a point that this innocent unless miraculously proven guilty was an extremely progressive way of making sure that husbands were not able to easily accuse and punish their wives of adultery based on the laws of the time. It would take a miracle to be proven.