We performed measurements of X-1(T, H-ac, f) and X-1(T, H-ac, f) on a nominal composition of Bi1.6Pb0.4Sr2Ca3Cu4O12 ceramic samples prepared by the liquid ammonium nitrate method. The effect of regrinding followed by 2 h of resintering at 840 degrees C of the fabricated samples have been investigated by ac susceptibility. XRD pattern and resistivity measurements were also carried out to characterize the samples. The experimental results were qualitatively discussed in the framework of the critical state model. Comparison of the observed results and the Clem model suggests that ac losses are dominated by hysteretic bulk pinning losses. Ac-irreversibility lines obtained from maximum ac dissipation at different frequencies fit quite well with the relation (1-T/T-c)similar to H-2/3.