In our modern language that would mean the strange quality in certain depressions in which one feels literally like lead. Without thinking of these alchemical similes, people often say: 'Today I feel like lead.'
Von Franz bridges the alchemical symbol of lead directly to clinical depression, arguing that lead's heaviness is the psychological correlate of libido that has sunk below the threshold of consciousness and must be consciously descended into.
, Alchemy: An Introduction to the Symbolism and the Psychology, 1980thesis