The molybdic acid may be obtained by roasting the sulphuret in a crucible and stirring it frequently; the sulphur in great part escapes in the form of sulphurous acid and the metal becomes oxidated: carbonate of soda in solution may be added to the residuum as long as any effervescence is observed; molybdate of soda remains in solution and the acid may be precipitated by nitric acid. The brown oxide is best obtained by heating molybdate of ammonia to red; the ammonia and part of the oxygen are expelled, and the brown oxide remains. There are two views with which the preceding results may be reconciled; namely, 1st. supposing the atom of molybdenum to weigh 21; and 2d, by supposing it to weigh 42 or twice that number. In the first case the brown oxide will weigh 24½ (49) being supposed 2 atoms of metal and 1 of oxygen, the blue or protoxide will weigh 28, and the white oxide or molybdic acid will weigh 63, being a compound of the protoxide and deutoxide, molybdena or native sulphuret will then be as usual, the protosulphuret, consisting of 21 metal and 14 sulphur, or 60 metal and 40 sulphur. In the 2d. case the brown or protoxide will weigh 49, the blue or deutoxide 56, and the acid or tritoxide 63. The native sulphuret, molybdena, must in this view be the deutosulphuret, or 42 metal and 28 sulphur. The former of these views exhibits the oxides somewhat complicated, but agrees well with the sulphuret; the latter shews the oxides in a more regular train, but does not appear so probable from the sulphuret; besides, the notion of a metallic tritoxide is rather singular, especially in a metal that is rarely if ever found in combination with oxygen. Upon the whole I prefer the former view; but it must be considered as problematical only. The atom of 60 (see page 267 VOL. 1) must doubtless be erroneous. 26. _Oxides of tungsten._