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atomic See also:weight 238.5 See also:URANIUM [See also:symbol U (0=16)] , a metallic chemical See also:element . In 1789 See also:Klaproth isolated from See also:pitchblende a yellow See also:oxide which he viewed as the oxide of a new See also:metal, which he named See also:uranium, after the newly discovered See also:planet of See also:Herschel . By reducing the oxide with See also:charcoal at a high temperature, he obtained a product which he took to be metallic uranium . See also:Berzelius about 1823 found that the yellow oxide, when treated with excess of sulphuric See also:acid, gave a sulphate not unlike the ferric See also:salt . He concluded that the uranium salt was Ur2033S03, where Ur203, according to his See also:analysis, represents 864 parts of yellow oxide (0=16) . Like Fe203, the yellow oxide lost 48 parts of See also:oxygen per Ur203 (= 864 parts) as See also:water, while Ur2 = 816 parts of metal remained . These results were adopted until Peligot in 184o discovered that Berzelius's (and Klaproth's) metal contains oxygen, and that his (Ur2)03 really is (UsOs)•03=3U203, where U=12o is one See also:equivalent See also:weight of real uranium . Peligot's results, though called in question by Berzelius, have been amply confirmed by all subsequent investigators; only now, on theoretical grounds, first set forth by Mendeleeff, we See also:double Peligot's atomic weight, so that U now signifies 240 parts of uranium, while UO3 stands as the See also:formula of the yellow oxide, and UO2 as that of Berzelius's metal . The only practically available raw material for the extraction of uranium is pitchblende (q.v.) . Pure pitchblende is U30s, which, in relatively See also:good specimens, forms some 8o% or more of the whole . It is remarkable as always containing See also:helium (q.v.) and radioactive elements (see See also:RADIOACTIVITY) . To See also:extract the metal, the pitchblende is first roasted in See also:order to remove the See also:arsenic and See also:sulphur . In one See also:process the purified ore is disintegrated with hot nitric acid to produce nitrates, which are then converted into sulphates by evaporation with sulphuric acid . The sulphates are treated with water, which dissolves the uranium and other soluble salts, while See also:silica, See also:lead sulphate, &c., remain; these are removed by filtration . From the See also:solution the arsenic, See also:copper, &c., are precipitated by sulphuretted See also:hydrogen as sulphides, which are filtered off . The filtrate contains the uranium as uranous and the See also:iron as ferrous salt . These are oxidized and precipitated conjointly by excess of See also:ammonia . The precipitate, after having been collected and washed, is digested with a warm concentrated solution of ammonium carbonate, which dissolves the uranium as a yellow solution of ammonium uranate, while the hydrated oxide of iron, the alumina, &c., remain . These are filtered off hot, and the filtrate is allowed to cool, when crystals of the uranate See also:separate out . The See also:mother liquor includes generally more or less of See also:nickel, See also:cobalt, See also:zinc and other heavy metals, which, as See also:Wohler showed, can be removed as insoluble sulphides by the addition of ammonium sulphide; uranium, under the circumstances, is not precipitated by this reagent . The filtrate, on being boiled down, yields a second See also:crop of uranate . This uranate when Waited in a See also:platinum crucible leaves a See also:green oxide of the See also:composition 30s, i.e. artificial pitchblende, which serves as a starting-point for the preparation of uranium compounds . The green oxide, as a See also:rule, requires to be further purified . One method for this purpose is to convert it into a solution of the nitrate UO2(NO3)2, and from it to precipitate the metal as oxalate by oxalic acid (Peligot) .
The latter (UO2•C204) yields a purer oxide, UO2, or, in the presence of See also:air, U808, on ignition
.
Metallic uranium, as shown by Peligot, can be obtained by the reduction of a .mixture of dry chloride of See also:potassium and dry uranous chloride, UCl4, with See also:sodium at a 'red See also:heat
.
A better process is that of H
.
See also:Moissan (Comp). rend., 1896, 122, p
.
1o88), in which the oxide is heated with See also:sugar charcoal in the electric See also:furnace
.
Uranium is a See also:
Uranium is chemically related to See also:chromium, See also:molybdenum and See also:tungsten
.
If forms two See also:series of salts, one, the uranous compounds, are derived from the oxide UO2, the other, the uranyl compounds, contain the divalent See also:group UO2
.
Uranous Compounds.—Uranium dioxide, UO2 (Berzelius's metal), is a See also: Uranyl or Uranic Compounds.—Uranic oxide, UO3 or UO2.0, is obtained by heating uranyl nitrate to 250° as a yellow solid, insoluble in water, but soluble in acids with the formation of uranyl salts . Various hydrates have been described, but they cannot be formed by precipitating a uranyl salt with an alkali, this reagent giving rise to salts termed uranates . These salts generally resemble the bichromates; they are yellow in See also:colour, insoluble in water, soluble in acids, and decomposed by heat . Sodium uranate, Na2U2O2, is used as a pigment for See also:painting on See also:glass and See also:porcelain under the name of uranium yellow . It is manufactured by heating pitchblende with See also:lime, treating the resulting See also:calcium uranate with dilute sulphuric acid, and adding sodium carbonate in excess . Dilute sulphuric acid precipitates uranium yellow, Na2U2O7.6H2O, from the solution so obtained . Ammonium uranate heated to redness yields pure U308, which serves as a raw material for uranium compounds . Uranyl nitrate, UO2(NO3)2.6H20, is the most important uranium salt . It is obtained as See also:fine See also:lemon yellow deliquescent prisms by evaporating a solution of any of the oxides in nitric acid . By See also:electrolysis it yields uranium dioxide as a pyrophoric powder, and peruranic hydroxide, U04.2H20, when treated with hydrogen peroxide . The latter gives rise to salts, the peruranates, e.g . (Na202)2U04.8H20 . Uranyl nitrate is used in See also:photography, and also in See also:analytical See also:chemistry as a precipitant for phosphoric acid (as uranyl ammonium phosphate, Up02.NH4•PO4) . Uranyl chloride, UO2C12, is a yellow crystalline See also:mass formed when chlorine is passed over uranium dioxide at a red heat . It is also obtained by dissolving the oxide in hydrochloric acid and evaporating . It forms double salts with metallic chlorides and with the hydrochlorides of organic bases . Uranyl sulphide, UO2S, is a black precipitate obtained by adding ammonium sulphide to a uranyl solution . Exposed to air this mixture is oxidized to the pigment uranium red, U2(NH4)2SO4, which is a fine See also:blood-coloured amorphous powder.' Analysis.—A borax See also:bead dissolves uranium oxides in the reducing See also:flame with a green, in the oxidizing flame with a yellow, colour . Solutions of uranyl salts (nitrate, &c.) behave to reagents as follows: sulphuretted hydrogen produces green uranous salt with precipitation of sulphur; sulphide of ammonium in neutral solutions gives a black precipitate of UO2S, which settles slowly and, while being washed in the See also:filter, breaks up partially into hydrated UO2 and sulphur; ammonia gives a yellow precipitate of uranate of ammonia, characteristically soluble in hot carbonate of ammonia solution; prussiate of potash gives a brown precipitate which in See also:appearance is not unlike the precipitate produced by the same reagent in cupric salts . |
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