A reaction cell for in situ studies of both ion-exchange and hydrother
mal titration reactions has been designed and built. This cell allows
the injection of reagents into a reaction mixture over time during X-r
ay data collection. A demonstration experiment followed the injection
of Na2SO4(aq) into BaCl2(aq) to yield a time-resolved X-ray powder dif
fraction pattern of the precipitation of BaSO4(s).