Mixed sulfur (a yellow solid) with iron filings (a black solid) in a ceramic dish called a crucible. then he separated them using a magnet. what kind of a change is this?

Consider a culture medium on which only gram-positive organisms such as staphylococcus aureus colonies can grow due to an elevated nacl level. a yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the ph as a result and changing the color of a ph indicator chemical. this type of medium would be referred to as a differential and enrichment culture.