There appear to be two oxides of uranium from the experiments of Klaproth, Bucholz, and Vauquelin; but the proportions of metal and oxygen have not been very nearly ascertained, from the great scarcity of the minerals containing this metal. (Vid. Bucholz, An. de Chimie, 56--142. Vauquelin, ibid. 68--277; or Nicholson’s Journ. 25--69). The oxides are obtained by precipitation from solutions of the minerals in the nitric or muriatic acid, the foreign substances being first separated. The protoxide of uranium precipitates dark bottle green by caustic alkalies, and forms crystallizable salts with acids; the other, probably the deutoxide, precipitates orange yellow, and forms uncrystallizable salts with acids; in these respects the oxides bear a near resemblance to those of iron. Bucholz estimates the yellow oxide at 100 metal + from 25 to 32 oxygen; as it yields oxymuriatic acid when treated with muriatic, it is most likely to be the deutoxide; now if we take 28 for the oxygen combined with 100 metal, the protoxide must consist of 100 metal + 14 oxygen, or of 50 metal + 7 oxygen, and the atom of uranium = 50. From his account of the sulphate and nitrate of uranium the weight of the atom might be inferred to be double of the above or 100. These different conclusions can only be elucidated by future experiments. 25. _Oxides of molybdenum._ The latest and as it should seem most accurate experiments on the oxides of molybdenum were made by Bucholz. (Vid. Nicholson’s Journal, 20, p. 121). There appear to be 3 oxides or combinations of molybdenum and oxygen, namely, the _brown_, the _blue_, and the _white_ or _yellow_. The two last have the character of acids, and none of them seem to form salts with acids, like oxides in general. Bucholz ascertained the above gradation, and that the white oxide or molybdic acid contains ⅓ of its weight of oxygen; (which has since been corroborated by Berzelius); he also found that the blue was best formed by mixing, triturating, and boiling in water 3 parts of brown oxide, and 4 of white, or one of metal, and two of acid; and that it has acid qualities as well as the white. Bucholz also found 3 parts of liquid ammonia of the sp. gr. .97 dissolve 1 of molybdic acid; now 3 parts of ammonia = .186 real (VOL. 1, p. 422); and 1 ∶ .186 ∷ 64 ∶ 12, the quantity of ammonia usually saturated by one atom of acid; and Berzelius found 100 molybdic acid saturate 155 oxide of lead, or 63 acid to 97 oxide. The native sulphuret of molybdenum (the state in which this metal is usually found) was analyzed by Bucholz and found to consist of 60 metal and 40 sulphur.