Final answer:
Alchemy is no longer practiced because its principles were disproven and replaced by the more accurate and scientific field of chemistry, with contributions from figures like Dalton and Avogadro leading to a shared and systematic understanding of matter.
Step-by-step explanation:
The practice of alchemy is not pursued today because it was based on a flawed understanding of matter and was superseded by the modern science of chemistry. Over centuries, systematic discoveries about substance properties and chemical reactions revealed immutable mass ratios in reactions, suggestive of underlying units like atoms and molecules. Key figures like John Dalton and Amedeo Avogadro contributed significantly to these developments, and notions such as Avogadro's number became cornerstones of chemistry, offering precise and predictable knowledge that alchemy never did.
Alchemy's secretive nature also limited its progress, as discoveries were not shared widely, inhibiting collective advancement. The transformation of 'base metals' like lead into 'noble metals' such as gold, a common goal of alchemists, was deemed impossible with the advent of an atomic understanding of elements. The historical shift from mystical and secretive practices of alchemy to more empirical, testable, and sharable knowledge marked the dawn of modern chemistry, which rendered alchemy obsolete.