  The shear viscosity eta_s(w) of dilute polymer solutions (of flexible coils)
has been classically measured and interpreted in terms of the Zimm modes. We
point out that the longitudinal viscosity eta_l(w) is the sum of two components
eta_l=4*eta_s/3+eta_p, where eta_p is due to an effect of pressure on the coil
size. We discuss eta_p for a crude model involving a dependence of both the
Kuhn length a and the Flory parameter chi on pressure. We find that eta_p is
comparable to eta_s for good solvent conditions, but that eta_p should dominate
over eta_s near the theta point.
