LIQUEFACTION AND SOLIDIFICATION OF AIR AND HYDROGEN. 163 
M. Pictet has recently found, both by calculation and ex- 
periment, that liquid oxygen is identical in density with 
water. 
But a few short months since and to have talked of being 
able to solidify hydrogen would have been idle ; to have be- 
lieved it impossible of accomplishment would have been deemed 
philosophical. 
