  We have developed a series expansion method for calculating the uniform
magnetization, M, as a function of the applied field h for Heisenberg systems
at T=0. The method involves introducing Ising anisotropy along the z-axis
together with an applied uniform field along the x-axis. On extrapolation to
the isotropic limit, one recovers the magnetization for the Heisenberg system
with an applied field along the x-axis. This method circumvents the
difficulties in developing perturbation theory associated with the commuting
nature of the uniform field. The results developed for two-chain ladders
appropriate for the material Cu_2(C_5H_{12}N_2)_2Cl_4 are in good agreement
with the experimental data. In addition, uniform susceptibility is calculated
by high temperature expansions and also compared with the experimental data.
