Light-metal hydride and amide systems are currently among the most promising materials for reversible hydrogen storage. In this proposal, we ask for 3 days on POLARIS or GEM to perform an in-situ gravimetric study of the facile formation of key components of these and related systems. Specifically in this initial proposal, we plan to investigate the crystallographic changes in deuterides of lithium, sodium, potassium and magnesium under ammonia pressure. Performing these systematic experiments in situ for the first time using our custom IGAn apparatus will further our understanding of light-metal hydride and amide systems with a view to utilising this information to develop a new generation of enhanced, reversible, hydrogen storage materials.