The structure and properties of the high-pressure phase of ammonia dihydrate, ADH-II, have been challenging to determine. However, the structure has been solved recently by application of density-functional-theory calculations, these being constrained only by the unit-cell indexing that I reported in 2009. DFT methods have also been used to compute the elastic constants, and have found axial incompressbilities that appear to be inconsistent with the known stiffness of the material as inferred from some crude high-pressure thermal expansion data. I propose to obtain high-resolution low-noise powder data, using a TiZr gas cell on OSIRIS, with which to obtain the best possible structure refinement, to measure the incompressibility on decompression at 100 K (where the material will likely persist metastably to 1 bar), and to re-measure - more accurately - the thermal expansion.