Note 6 bis — Chapter XXI · CHROMIUM, MOLYBDENUM, TUNGSTEN, URANIUM, AND MANGANESE

Now that persulphuric acid H2S2O8 is well known it might be supposed that perchromic anhydride, Cr2O7, would correspond to perchromic acid, H2Cr2O8, but as yet it is not certain whether corresponding salts are formed. Péchard (1891) on adding an excess of H2O2 and baryta water to a dilute solution of CrO2 (8 grm. per litre), observed the formation of a yellow precipitate, but oxygen was disengaged at the same time and the precipitate (which easily exploded when dried) was found to contain, besides an admixture of BaO2, a compound BaCrO5, and this = BaO2 + CrO3, and does not correspond to perchromic acid. The fact of its decomposing with an explosion, and the mode of its preparation, proves, however, that this is a similar derivative of peroxide of hydrogen to persulphuric acid (Chapter XX.)