  We present a study of the main bulk properties (susceptibility,
magnetization, resistivity and specific heat) of CePt_3B_(1-x)Si-x, an alloying
system that crystallizes in a noncentrosymmetric lattice, and derive the
magnetic phase diagram. The materials at the end point of the alloying series
have previously been studied, with CePt_3B established as a material with two
different magnetic phases at low temperatures (antiferromagnetic below T_N =
7.8 K, weakly ferromagnetic below T_C ~ 5 K), while CePt3Si is a heavy fermion
superconductor (T_c = 0.75 K) coexisting with antiferromagnetism (T_N = 2.2 K).
From our experiments we conclude that the magnetic phase diagram is divided
into two regions. In the region of low Si content (up to x ~ 0.7) the material
properties resemble those of CePt3B. Upon increasing the Si concentration
further the magnetic ground state continuously transforms into that of CePt3Si.
In essence, we argue that CePt_3B can be understood as a low pressure variant
of CePt3Si.
