  Thermal expansion data are used to study the uniaxial pressure dependence of
the electronic/magnetic entropy of Ba(Fe1-xCox)2As2. Uniaxial pressure is found
to be proportional to doping and, thus, also an appropriate tuning parameter in
this system. Many of the features predicted to occur for a pressure-tuned
quantum critical system, in which superconductivity is an emergent phase hiding
the critical point, are observed. The electronic/magnetic Gr\"uneisen
parameters associated with the spin-density wave and superconducting
transitions further demonstrate an intimate connection between both ordering
phenomena.
