Expanded Comment on: Optical Properties of Fluid Hydrogen at the   Transition to a Conducting State
  We comment on a recent paper published by McWilliams et al claiming that high-pressure/high-temperature hydrogen is a semi-conductor or semi-metal, in conflict with all earlier measurements on this system which show that it is metallic. We point out problems and inconsistencies and propose an alternate interpretation such that their results can be compatible with the observation of metallic hydrogen. 
Isaac F. Silvera, Rachel Husband, Ashkan Salamat, Mohamed Zaghoo
cond-mat.mtrl-sci cond-mat.other