def schmdt_nmbr(diffusivity, kinematic_viscosity = 10**-6):
    """
    Return the Schmidt number []

    Parameters
    ----------
    kinematic_viscosity : kinematic viscosity of water (defautl 10^-6)[m²/s]
    diffusivity : mass diffusivity of the chemical in water [m²/s]


    """
    return kinematic_viscosity / diffusivity