This study gives calculation of the specific heat CVI of NH4Cl and NH4BrxCl1-x under the Ising model for the transition between the disordered (D) and ferro-ordered O(F) phases in these crystalline systems. Our CVI values which we calculated for x = 0 and x = 0.04, agree both below and above Tc with the observed Cp data from the literature. Our value of a 0.1 (T < Tc and T > Tc) is in good agreement with the predicted value of 1/8 (0.125) of a 3D Ising model.