What the work claims
Diffusion in fluids follows two quantitative laws: (1) flux is proportional to the concentration gradient; (2) the gradient changes over time in a way described by a partial differential equation identical to the diffusion equation.
How it was done
Adolf Fick conducted experiments in 1855 using salt solutions diffusing between two reservoirs through water-filled tubes. His method followed Graham’s earlier work and measured concentrations and fluxes directly.
What holds up
The first law holds: diffusive flux is directly proportional to the concentration gradient. The second law holds: it correctly predicts how concentration gradients evolve over time in fluids. Both laws are mathematically linked — the second follows from the first and matches the diffusion equation.
What does not
It does not apply to solids: diffusion in solids was not considered generally possible at the time, and Fick made no claim about it.
Why it matters beyond the lab
It underpins drug delivery, dialysis, semiconductor doping, atmospheric modelling and food preservation — wherever mass moves down a concentration gradient in a fluid medium.
Is it worth your time
Yes — it is the foundational quantitative framework for diffusion in fluids, still used across chemistry, medicine and materials science. Its simplicity and empirical grounding make it worth understanding deeply.