On Alchemy

I've had a few questions regarding what is meant by alchemy. The reading, Fruits of Free Trade, references the term in the context of some magical creation of gains from trade. Alchemy, often thought of as a branch of chemistry, is the mythical practice of turning lead into gold (Pb -> Au). Alchemy was often believed to be practiced by wizards.

The keyword is "mythical". If lead could indeed be turned to gold it would, at first thought, seem to be wealth-creating. However, if one thinks that alchemy could, indeed, turn lead into gold, gold would no longer be as scarce and, hence, no longer of value.

Anyway, for the paper, you are to think about how "gains" from trade are generated. Is it magical? If not, what gives rise to the ability to increase overall consumption?