> hydrogen is just a pain in the royal order to use too, its density is just > so very very low. Metal Hydrides show promise. The LOW molecular weight, clean combustion and uniquely high energy per mol make it an attractive target, density notwithstanding. FWIW, LIQUID hydrogen has a density 14 times lower than eg liquid air! RM -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu