Nitrides of alkali and alkaline earth metals are an interesting set of materials specifically for their potential in reversible hydrogen storage. However, many fundamental challenges remain. This proposal looks to explore the interaction of intermediate phases during the hydrogenation (exposure to H2 gas) of a pellet of Ca3N2. A previous experiment at RAL (RB 1410181) showed that when a pellet of CaH2 was nitrided (exposed to N2 gas) the conductivity increased drastically. We are interested if a similar result will occur from the inverse reaction. The intermediate phases between calcium nitride and calcium nitride hydride (Ca2NH) play a significant role in reducing the materials resistance to ion conduction and also to the reversible storage of hydrogen. We will use Polaris to investigate these intermediate phases by step exposure of the pellet to hydrogen gas followed by long diffractio