A detailed experimental investigation of the linear and non-linear Ac susceptibilities of two ferromagnetic samples, namely PdMn with 0.75 at.% Mn and PdFe with 0.17 at.% Fe, has been carried out as a function of temperature, frequency and amplitude of the Ac driving field. In order to explain this behaviour, we have also developed a very simple theory for ferromagnetics, based upon the mean-field model. For these samples the expected divergence of the higher-order susceptibility (X) over tilde(nl) at T-c does not occur; instead the measured response tends to zero. According to this theory, the correction term for demagnetization effects seems to outweigh the critical divergence in (X) over tilde(nl) at T --> T-c. The extreme sensitivity of (X) over tilde(nl) to demagnetization correction is not generally recognized in the recent literature. To obtain the transition temperatures and the critical exponent gamma of the samples, the well known Kouvel-Fisher method is used. We have found T-c = 1.95 +/- 0.02 K for PdFe and T-c = 2.65 +/- 0.02 K for PdMn. For PdMn and PdFe, the values of gamma are calculated to be 1.41 +/- 0.05 and 1.55 +/- 0.05, respectively.