It is well known that chemists have usually admitted the existence of two gaseous compounds of phosphorus and hydrogen,—one spontaneously inflammable, the other not so. Of late, Rose of Berlin has ascertained that both gases are identical in composition, and has consequently been led to infer that the existence of two phosphuretted-hydrogens, differing so much in properties, and yet similarly composed, constitutes an example of isomerism among gaseous bodies.