Did alchemy really exist in antiquity?

Yes. The idea of alchemy has been around for thousands of years. Even up to the eighteenth century scientists such as Isaac Newton were still practicing alchemy. Today we can transmute base elements inside particle accelerators, it's just more trouble and energy than it is worth.

Hundreds of years ago the belief in alchemy wasn't considered that far-fetched by the educated. The Bible itself says Jesus turned water into wine and people observed in nature such phenomenon as solid wood burning and becoming a smoke gas. There was also the belief that "spontaneous generation" caused nonliving matter would become living organisms. Now with atomic theory and molecular biology we can have a true understanding of what couldn't be explained during those past years.

There were even alchemy scams in the past. Scammers would show up in a kingdom with a piece of lead and "treat it" so it would become gold. Of course, the lead was really gold with a lead coating. The scam artist would do something like splash chemicals on the piece of lead and heat it in fire. Since lead has a much lower melting point than gold the lead would melt off exposing the gold.